Alesis 3630 User manual

Reference Manual
2002

Important Safety
Instructions
Important Safety Instructions (English)
Safety symbols used in this product
This symbol alerts the user that there are important operating and
maintenance instructions in the literature accompanying this unit.
This symbol warns the user of uninsulated voltage within the unit that
can cause dangerous electric shocks.
This symbol warns the user that output connectors contain voltages that
can cause dangerous electrical shock.
Please follow these precautions when using this
product:
1. Read these instructions.
2. Keep these instructions.
3. Heed all warnings.
4. Follow all instructions.
5. Do not use this apparatus near water.
6. Clean only with a damp cloth. Do not spray any liquid cleaner onto the
faceplate, as this may damage the front panel controls or cause a dangerous
condition.
7. Install in accordance with the manufacturer's instructions.
8. Do not install near any heat sources such as radiators, heat registers, stoves, or
other apparatus (including amplifiers) that produce heat.
9. Do not defeat the safety purpose of the polarized or grounding-type plug. A
polarized plug has two blades with one wider than the other. A grounding-
type plug has two blades and a third grounding prong. The wide blade or the
third prong are provided for your safety. When the provided plug does not fit
into your outlet, consult an electrician for replacement of the obsolete outlet.
10. Protect the power cord from being walked on or pinched, particularly at plugs,
convenience receptacles, and the point where they exit from the apparatus.
11. Use only attachments or accessories specified by the manufacturer.
Continued next page

Important Safety Instructions
12. Use only with a cart, stand, bracket, or table designed for use with
professional audio or music equipment. In any installation, make sure that
injury or damage will not result from cables pulling on the apparatus and its
mounting. If a cart is used, use caution when moving the cart/apparatus
combination to avoid injury from tip-over.
13. Unplug this apparatus during lightning storms or when unused for long
periods of time.
14. Refer all servicing to qualified service personnel. Servicing is required when
the apparatus has been damaged in any way, such as when the power-supply
cord or plug is damaged, liquid has been spilled or objects have fallen into the
apparatus, the apparatus has been exposed to rain or moisture, does not
operate normally, or has been dropped.
15. This unit produces heat when operated normally. Operate in a well-ventilated
area with at least six inches of clearance from peripheral equipment.
16. This product, in combination with an amplifier and headphones or speakers,
may be capable of producing sound levels that could cause permanent hearing
loss. Do not operate for a long period of time at a high volume level or at a
level that is uncomfortable. If you experience any hearing loss or ringing in
the ears, you should consult an audiologist.
17. Do not expose the apparatus to dripping or splashing. Do not place objects
filled with liquids (flower vases, soft drink cans, coffee cups) on the apparatus.
18. WARNING: To reduce the risk of fire or electric shock, do not expose this
apparatus to rain or moisture.

Important Safety Instructions
Instructions de Sécurité Importantes
(French)
Symboles utilisés dans ce produit
Ce symbole alèrte l’utilisateur qu’il existe des instructions de
fonctionnement et de maintenance dans la documentation jointe avec ce produit.
Ce symbole avertit l’utilisateur de la présence d’une tension non isolée à
l’intérieur de l’appareil pouvant engendrer des chocs électriques.
Ce symbole prévient l'utilisateur de la présence de tensions sur les
raccordements de sorties, représentant un risque d'électrocution.
Veuillez suivre ces précautions lors de l’utilisation de
l’appareil:
1. Lisez ces instructions.
2. Gardez ces instructions.
3. Tenez compte de tous les avertissements.
4. Suivez toutes les instructions.
5. N’utilisez pas cet allareil à proximité de l’eau.
6. Ne nettoyez qu’avec un chiffon humide. Il est potentiellement dangereux
d'utiliser des pulvérisateurs ou nettoyants liquides sur cet appareil.
7. Installez selon les recommandations du constructeur.
8. Ne pas installer à proximilé de sources de chaleur comme radiateurs, cuisinière
ou autre appareils (don’t les amplificateurs) produisant de la chaleur.
9. Ne pas enlever la prise de terre du cordon secteur. Une prise murale avec
terre deux broches et une troisièrme reliée à la terre. Cette dernière est
présente pour votre sécurité. Si le cordon secteur ne rentre pas dans la prise
de courant, demandez à un électricien qualifié de remplacer la prise.
10. Evitez de marcher sur le cordon secteur ou de le pincer, en particulier au
niveau de la prise, et aux endroits où il sor de l’appareil.
11. N’utilisez que des accessoires spécifiés par le constructeur.
Suite de la page suivante

Important Safety Instructions
12. N’utilisez qu’avec un stand, ou table conçus pour l’utilisation d’audio
professionnel ou instruments de musique. Dans toute installation, veillez de
ne rien endommager à cause de câbles qui tirent sur des appareils et leur
support.
13. Débranchez l’appareil lors d’un orage ou lorsqu’il n’est pas utilisé pendant
longtemps.
14. Faites réparer par un personnel qualifié. Une réparation est nécessaire lorsque
l’appareil a été endommagé de quelque sorte que ce soit, par exemple losrque
le cordon secteur ou la prise sont endommagés, si du liquide a coulé ou des
objets se sont introduits dans l’appareil, si celui-ci a été exposé à la pluie ou à
l’humidité, ne fonctionne pas normalement ou est tombé.
15. Puisque son fonctionement normale génère de la chaleur, placez cet appareil
au moins 15cm. des équipments péripheriques et assurez que l’emplacement
permet la circulation de l’air.
16. Ce produit, utilisé avec un amplificateur et un casque ou des enceintes, est
capable de produite des niveaux sonores pouvant engendrer une perte
permanente de l’ouïe. Ne l’utilisez pas pendant longtemps à un niveau sonore
élevé ou à un niveau non confortable. Si vous remarquez une perte de l’ouïe
ou un bourdonnement dans les oreilles, consultez un spécialiste.
17. N'exposez pas l'appareil à l'égoutture ou à l'éclaboussement. Ne placez pas les
objets remplis de liquides (vases à fleur, boîtes de boisson non alcoolique,
tasses de café) sur l'appareil.
18. AVERTISSEMENT: Pour réduire le risque du feu ou de décharge électrique,
n'exposez pas cet appareil à la pluie ou à l'humidité.

Important Safety Instructions
Lesen Sie bitte die folgende
Sicherheitshinweise (German)
Sicherheit Symbole verwendet in diesem Produkt
Dieses Symbol alarmiert den Benutzer, daß es wichtige Funktionieren
und Wartung Anweisungen in der Literatur gibt, die diese Maßeinheit begleitet.
Dieses Symbol warnt den Benutzer der nicht isolierten Spannung
innerhalb der Maßeinheit, die gefährliche elektrische Schläge verursachen kann.
Dieses Symbol warnt den Benutzer, dem Ausgabestecker Spannungen
enthalten, die gefährlichen elektrischen Schlag verursachen können.
Folgen Sie bitte diesen Vorkehrungen, wenn dieses
Produkt verwendet wird:
1. Lesen Sie die Hinweise.
2. Halten Sie sich an die Anleitung.
3. Beachten Sie alle Warnungen.
4. Beachten Sie alle Hinweise.
5. Bringen Sie das Gerät nie mit Wasser in Berührung.
6. Verwenden Sie zur Reinigung nur ein weiches Tuch. Verwenden Sie keine
flüssigen Reinigungsmittel. Dies kann gefährliche Folgen haben.
7. Halten Sie sich beim Aufbau des Gerätes an die Angaben des Herstellers.
8. Stellen Sie das Gerät nich in der Nähe von Heizkörpern, Heizungsklappen
oder anderen Wärmequellen (einschließlich Verstärkern) auf.
9. Verfehlen Sie nicht den Zweck des grounging Terminals auf dem Netzstecker.
Dieses Terminal wird für Ihre Sicherheit zur Verfügung gestellt.
10. Verlegen Sie das Netzkabel des Gerätes niemals so, daß man darüber stolpern
kann oder daß es gequetscht wird.
11. Benutzen Sie nur das vom Hersteller empfohlene Zubehör.
Fortsetzung auf nächster Seite

Important Safety Instructions
12. Verwenden Sie ausschließlich Wagen, Ständer, oder Tische, die speziell für
professionelle Audio- und Musikinstrumente geeignet sind. Achten Sie immer
darauf, daß die jeweiligen Geräte sicher installiert sind, um Schäden und
Verletzungen zu vermeiden. Wenn Sie einen Rollwagen benutzen, achten Sie
darauf, das dieser nicht umkippt, um Verletzungen auszuschließen.
13. Ziehen Sie während eines Gewitters oder wenn Sie das Gerät über einen
längeren Zeitraum nicht benutzen den Netzstecher aus der Steckdose.
14. Die Wartung sollte nur durch qualifiziertes Fachpersonal erfolgen. Die
Wartung wird notwendig, wenn das Gerät beschädigt wurde oder aber das
Stromkabel oder der Stecker, Gegenstände oder Flüssigkeit in das Gerät
gelangt sind, das Gerät dem Regen oder Feuchtigkeit ausgesetzt war und
deshalb nicht mehr normal arbeitet oder heruntergefallen ist.
15. Dieses Gerät produziert auch im normalen Betrieb Wärme. Achten Sie
deshalb auf ausreichende Lüftung mit mindestens 15 cm Abstand von
anderen Geräten.
16. Dieses Produkt kann in Verbindung mit einem Verstärker und Kopfhörern
oder Lautsprechern Lautstärkepegel erzeugen, die anhaltende Gehörschäden
verursachen. Betreiben Sie es nicht über längere Zeit mit hoher Lautstärke
oder einem Pegel, der Ihnen unangenehm is. Wenn Sie ein Nachlassen des
Gehörs oder ein Klingeln in den Ohren feststellen, sollten Sie einen
Ohrenarzt aufsuchen.
17. Setzen Sie den Apparat nicht Bratenfett oder dem Spritzen aus. Plazieren Sie
die Nachrichten, die mit Flüssigkeiten (gefüllt werden Blumevases,
Getränkdosen, Kaffeetassen) nicht auf den Apparat.
18. WARNING: um die Gefahr des Feuers oder des elektrischen Schlages zu
verringern, setzen Sie diesen Apparat nicht Regen oder Feuchtigkeit aus.

CE Declaration Of Conformity
See our website at:
http://www.alesis.com
FCC Compliance Statement
This device complies with Part 15 of the FCC rules. Operation is subject to the
following two conditions: (1) This device may not cause harmful interference and
(2) this device must accept any interference received, including interference that
may cause undesired operation.
NOTE: This equipment has been tested and found to comply with the limits for
a Class B digital device, pursuant to Part 15 of the FCC Rules. These limits are
designed to provide reasonable protection against harmful interference in a
residential installation. This equipment generates, uses and can radiate radio
frequency energy and, if not installed and used in accordance with the
instructions, may cause harmful interference to radio communications. However,
there is no guarantee that interference will not occur in a particular installation.
If this equipment does cause harmful interference to radio or television
reception, which can be determined by turning the equipment off and on, the
user is encouraged to try to correct the interference by one or more of the
following measures:
-- Reorient or relocate the receiving antenna.
-- Increase the separation between the equipment and receiver.
-- Connect the equipment into an outlet on a circuit different from that to which
the receiver is connected.
-- Consult the dealer or an experienced radio/TV
technician for help.

TABLE OF CONTENTS
Introduction ………….…………………………………………………..1
Hookup, General Tips …………………………………………………..2
Hooking Up Power ……………………………………………………...4
Front Panel Compressor / Limiter Controls ………………………….4
Front Panel Compressor / Limiter Switches ………………………….7
Front Panel Noise Gate Controls ……………………………………….8
Front Panel Metering …………………………………………………….9
Side Chain Applications ……………………………………………….10
Troubleshooting …………………….…………………………………..13
Specifications ……………………………………………………………14
APPENDIX: About Compression, Limiting, and Noise Gating …...15
Block Diagram …………………………………………………………..20

1
1.1 INTRODUCTION
Thank you for purchasing the Alesis 3630 Dual Channel Compressor/
Limiter with Gate. This cost-effective gain control device complements
any studio with several important features. For more information on the
significance of these features, refer to the Appendix "About Compression
and Limiting."
• Stereo or dual mono operation. The 3630 can serve as two totally in-
dependent units, or both sections can be strapped together for stereo
operation. In stereo, gain changes in one section are "tracked" by the
other section to eliminate wandering of the stereo image.
• Peak or RMS response. Determines whether the limiter will base its
operation on signal peaks or average signal levels. Each has its uses with
different types of signals (for example, peak with drums, and average
with complex program material).
• "Hard knee" or "soft knee" response. Each type of response gives a
different limiting action. The hard knee response is generally considered
more "severe," and the soft knee response, more "musical."
• Individual bypass switches for each channel. This makes it easy to
compare the processed and unprocessed sounds.
• Side chain connections. Insert EQs and other devices for applications
such as de-essing (removing sibilance), adding treble to limited signals,
"keying" one signal with another, "ducking" (e.g., making a signal such as
background music become lower in volume in response to another
signal, such as narration), and other applications.
• +4 dBu or -10dBV operation. This provides signal level compatibility
with nearly all studio setups.
• Front panel knob calibrations. Knobs are calibrated to allow for easy
setup and operation.
• Built-in stereo/dual mono noise gate. This can reduce noise when
compressing or limiting. Each section can also operate as a stand-alone
noise gate.
• Extensive metering. Each channel has a 12-LED display to indicate the
amount of gain reduction, a second 12-LED display to show input/
output levels, and a dual-LED display to indicate noise gate status.
Here are some typical applications for the 3630:
• Even out a vocalist's dynamics to compensate for poor mic or vocal
technique.
• Increase a guitar's (or other stringed instrument's) sustain.
2
• Smooth out bass sounds for a more consistent level.
• Prevent peaks common in many source signals, such as drums, from
overloading tape during recording.
• Minimize the chance of speaker burnout by inserting a limiter prior to
the power amp.
• Decrease a signal's dynamic range to accommodate a recording medium
with a more limited dynamic range (e.g., process a master tape mixed
for CD duplication when making cassette copies to accommodate the
cassette's limited dynamic range).
• In PA applications, limiting can increase a vocalist's level before
feedback occurs.
• Reduce sharp signal peaks associated with some signal processors and
highly resonant synthesizer patches.
• Remove hiss from tape, guitar amps, etc. with the noise gates.
• Use the noise gate to "key" one instrument's rhythm to another in-
strument.
• Use the sidechain to remove excessive sibilance from vocals and nar-
ration (commonly known as "de-essing").
• Use the sidechain for lowering background music or other program
material in the prescence of narration (commonly known as ducking).
1.2 HOOKUP: GENERAL TIPS
Rear Panel Connections
Each channel has its own set of rear panel 1/4" phone jacks.
Input Plug in the output of low or line level signals to be limited,
compressed, or gated. These outputs can be a stereo pair or individual
mono outputs from mixing consoles, crossovers, tape recorder channels,
synthesizers, and other unbalanced signal sources.
Microphones and guitars can be used with the level switch set to -10dBV
(see below). Guitars with exceptionally low output pickups may require a
preamp for best results. The input impedance is greater than 100kΩ.

1
1.1 INTRODUCTION
Thank you for purchasing the Alesis 3630 Dual Channel Compressor/
Limiter with Gate. This cost-effective gain control device complements
any studio with several important features. For more information on the
significance of these features, refer to the Appendix "About Compression
and Limiting."
• Stereo or dual mono operation. The 3630 can serve as two totally in-
dependent units, or both sections can be strapped together for stereo
operation. In stereo, gain changes in one section are "tracked" by the
other section to eliminate wandering of the stereo image.
• Peak or RMS response. Determines whether the limiter will base its
operation on signal peaks or average signal levels. Each has its uses with
different types of signals (for example, peak with drums, and average
with complex program material).
• "Hard knee" or "soft knee" response. Each type of response gives a
different limiting action. The hard knee response is generally considered
more "severe," and the soft knee response, more "musical."
• Individual bypass switches for each channel. This makes it easy to
compare the processed and unprocessed sounds.
• Side chain connections. Insert EQs and other devices for applications
such as de-essing (removing sibilance), adding treble to limited signals,
"keying" one signal with another, "ducking" (e.g., making a signal such as
background music become lower in volume in response to another
signal, such as narration), and other applications.
• +4 dBu or -10dBV operation. This provides signal level compatibility
with nearly all studio setups.
• Front panel knob calibrations. Knobs are calibrated to allow for easy
setup and operation.
• Built-in stereo/dual mono noise gate. This can reduce noise when
compressing or limiting. Each section can also operate as a stand-alone
noise gate.
• Extensive metering. Each channel has a 12-LED display to indicate the
amount of gain reduction, a second 12-LED display to show input/
output levels, and a dual-LED display to indicate noise gate status.
Here are some typical applications for the 3630:
• Even out a vocalist's dynamics to compensate for poor mic or vocal
technique.
• Increase a guitar's (or other stringed instrument's) sustain.
2
• Smooth out bass sounds for a more consistent level.
• Prevent peaks common in many source signals, such as drums, from
overloading tape during recording.
• Minimize the chance of speaker burnout by inserting a limiter prior to
the power amp.
• Decrease a signal's dynamic range to accommodate a recording medium
with a more limited dynamic range (e.g., process a master tape mixed
for CD duplication when making cassette copies to accommodate the
cassette's limited dynamic range).
• In PA applications, limiting can increase a vocalist's level before
feedback occurs.
• Reduce sharp signal peaks associated with some signal processors and
highly resonant synthesizer patches.
• Remove hiss from tape, guitar amps, etc. with the noise gates.
• Use the noise gate to "key" one instrument's rhythm to another in-
strument.
• Use the sidechain to remove excessive sibilance from vocals and nar-
ration (commonly known as "de-essing").
• Use the sidechain for lowering background music or other program
material in the prescence of narration (commonly known as ducking).
1.2 HOOKUP: GENERAL TIPS
Rear Panel Connections
Each channel has its own set of rear panel 1/4" phone jacks.
Input Plug in the output of low or line level signals to be limited,
compressed, or gated. These outputs can be a stereo pair or individual
mono outputs from mixing consoles, crossovers, tape recorder channels,
synthesizers, and other unbalanced signal sources.
Microphones and guitars can be used with the level switch set to -10dBV
(see below). Guitars with exceptionally low output pickups may require a
preamp for best results. The input impedance is greater than 100kΩ.

3
Side chain This stereo jack allows for insertion of other signal processors
or "keying" from other signal sources. See section 1.8 for side chain
applications.
Output Provides the processed (compressed/limited/gated) output. The
output impedance is 470Ω, unbalanced. Output level covers a nominal -20
to +20 dB range.
+4 dBu or -10dBV switch Use this switch to match each channel of the
3630 to the rest of your gear. Generally equipment designed for larger
pro studios tend to use +4 dBu nominal signal levels. Equipment designed
for smaller project and home studios and electronic musical instruments
tend to use -10dBV nominal signal levels. If the input signal doesn't
provide enough drive to the LED meters, use the -10dBV position. If
distortion occurs, use the +4 dBu position.
Changing the switch position modifies the way the input/output meter
references signals. When set to the +4 dBu position, a 4 dBu input signal
reads 0 dB on the input/output meter. When set to the -10dBV position, a
-10dBV input signal reads 0 dB on the input/output meter. When the unit
is set up for unity gain (no compression, output at 0) the input level will be
equal to the output level regardless of the position of the +4 dBu/-10 dBV
switch.
Installation
For most applications the 3630 will be installed in a rack frame. The 3630
generates very little heat so it is not necessary to leave an empty space for
ventilation above or below the unit.
4
1.3 HOOKING UP POWER
Hooking up power involves the rear panel power jack and front panel on-
off switch.
Power jack Plug the AC adapter output in here. Use only the AC adapter
supplied with the 3630; use of any other AC adapter will void your
warranty. To prolong the AC adapter's life, unplug it when not in use
(turning the 3630's power switch to off is not sufficient to disconnect the
AC adapter from AC power). Alesis recommends plugging your AC-
powered devices into a switched barrier strip, so that turning off the
barrier strip turns off power to your gear.
On/Off switch Press in to turn on. Press again (switch goes to the out
position) to turn off.
1.4 FRONT PANEL COMPRESSOR/
LIMITER CONTROLS
The front panel controls for the two compressor/limiter channels are
identical. The Channel A controls are located between the power switch
and Stereo Link switch in the middle of the panel. The Channel B controls
are located to the right of the Stereo Link switch. The Stereo Link switch
controls whether the two channels will operate as a stereo limiter or two
mono limiters, as described in section 1.5.
Since both channel controls operate identically, only the left channel
controls will be described.
Important: If you are not familiar with compressors, limiters, and noise
gates, refer to the Appendix. It contains theory necessary to understand
the following control descriptions.

3
Side chain This stereo jack allows for insertion of other signal processors
or "keying" from other signal sources. See section 1.8 for side chain
applications.
Output Provides the processed (compressed/limited/gated) output. The
output impedance is 470Ω, unbalanced. Output level covers a nominal -20
to +20 dB range.
+4 dBu or -10dBV switch Use this switch to match each channel of the
3630 to the rest of your gear. Generally equipment designed for larger
pro studios tend to use +4 dBu nominal signal levels. Equipment designed
for smaller project and home studios and electronic musical instruments
tend to use -10dBV nominal signal levels. If the input signal doesn't
provide enough drive to the LED meters, use the -10dBV position. If
distortion occurs, use the +4 dBu position.
Changing the switch position modifies the way the input/output meter
references signals. When set to the +4 dBu position, a 4 dBu input signal
reads 0 dB on the input/output meter. When set to the -10dBV position, a
-10dBV input signal reads 0 dB on the input/output meter. When the unit
is set up for unity gain (no compression, output at 0) the input level will be
equal to the output level regardless of the position of the +4 dBu/-10 dBV
switch.
Installation
For most applications the 3630 will be installed in a rack frame. The 3630
generates very little heat so it is not necessary to leave an empty space for
ventilation above or below the unit.
4
1.3 HOOKING UP POWER
Hooking up power involves the rear panel power jack and front panel on-
off switch.
Power jack Plug the AC adapter output in here. Use only the AC adapter
supplied with the 3630; use of any other AC adapter will void your
warranty. To prolong the AC adapter's life, unplug it when not in use
(turning the 3630's power switch to off is not sufficient to disconnect the
AC adapter from AC power). Alesis recommends plugging your AC-
powered devices into a switched barrier strip, so that turning off the
barrier strip turns off power to your gear.
On/Off switch Press in to turn on. Press again (switch goes to the out
position) to turn off.
1.4 FRONT PANEL COMPRESSOR/
LIMITER CONTROLS
The front panel controls for the two compressor/limiter channels are
identical. The Channel A controls are located between the power switch
and Stereo Link switch in the middle of the panel. The Channel B controls
are located to the right of the Stereo Link switch. The Stereo Link switch
controls whether the two channels will operate as a stereo limiter or two
mono limiters, as described in section 1.5.
Since both channel controls operate identically, only the left channel
controls will be described.
Important: If you are not familiar with compressors, limiters, and noise
gates, refer to the Appendix. It contains theory necessary to understand
the following control descriptions.

5
Threshold (-40 to +20 dBu)
Sets the level above which signals will be compressed or limited. Rotating
the control clockwise raises the threshold, thus clamping signals at a
higher level and reducing the amount of compression or limiting.
Ratio (1:1 to ∞:1)
Sets the compression slope, which determines how the output signal will
change in relation to the input signal once the input signal exceeds the
threshold. The first digit indicates how many dB of input change will cause
a 1 dB output change. The higher the ratio, the greater the compression,
and the more "squeezed" the sound.
Examples: With a setting of 2:1, a 2 dB input change for signals above the
threshold results in a 1 dB output change. With a setting of 1:1, a 1 dB
input change results in a 1dB output change (i.e., there is no change to the
signal dynamics). With a setting of ∞:1, the output level remains virtually
constant regardless of input level changes.
Attack (0.1 ms to 200 ms)
This control works only with the Peak/RMS switch (section 1.5) in Peak
mode. RMS mode automatically adjusts the attack time, depending on the
characteristics of the signals being processed.
6
In peak mode, this control sets how fast the limiter's internal circuitry reacts
to changes in input level. The longer the attack time, the more of a signal's
dynamics are "let through" before the limiting action kicks in. With slower
attack times, the limiter responds more to average signal level. This
produces a smoother sound that tends to retain dynamic character, but
the tradeoff is that the 3630 cannot react as rapidly to sudden level shifts.
Examples: Setting a longer attack time with guitar allows more of the pick
attack to come through. A longer attack time with kick drum lets through
more of the beater "thock." For recording, you may want to trade off
response time for smoothness. When used to prevent loudspeaker or
power amp clipping, a fast attack time is desirable.
Release (50 ms to 3 seconds)
This control works only with the Peak/RMS switch (section 1.5) in Peak
mode. RMS mode automatically adjusts the release time, depending on
the characteristics of the signals being processed.
In peak mode, this control determines how long it takes for the limiter to
return to unity gain after going into limiting. With short release times, the
limiter tracks every little change in level, producing a potentially uneven
or "rippling" effect that decreases dynamics but increases the average
output level. Longer release times tend to "squash" the signal more,
producing less overall output but retaining more of the signal's dynamics.
Excessive release times can be used as an effect. In the 60s using lots of
limiting with long release time on drums was a popular recording
technique.
Output (-20 to +20 dB)
The process of reducing dynamics lowers the signal's overall level. Use
this control to compensate by adding output gain.
Example: Limiting a signal by 6 dB will make the signal seem
approximately 6 dB softer. Compensate by using this control to increase
the level.

5
Threshold (-40 to +20 dBu)
Sets the level above which signals will be compressed or limited. Rotating
the control clockwise raises the threshold, thus clamping signals at a
higher level and reducing the amount of compression or limiting.
Ratio (1:1 to ∞:1)
Sets the compression slope, which determines how the output signal will
change in relation to the input signal once the input signal exceeds the
threshold. The first digit indicates how many dB of input change will cause
a 1 dB output change. The higher the ratio, the greater the compression,
and the more "squeezed" the sound.
Examples: With a setting of 2:1, a 2 dB input change for signals above the
threshold results in a 1 dB output change. With a setting of 1:1, a 1 dB
input change results in a 1dB output change (i.e., there is no change to the
signal dynamics). With a setting of ∞:1, the output level remains virtually
constant regardless of input level changes.
Attack (0.1 ms to 200 ms)
This control works only with the Peak/RMS switch (section 1.5) in Peak
mode. RMS mode automatically adjusts the attack time, depending on the
characteristics of the signals being processed.
6
In peak mode, this control sets how fast the limiter's internal circuitry reacts
to changes in input level. The longer the attack time, the more of a signal's
dynamics are "let through" before the limiting action kicks in. With slower
attack times, the limiter responds more to average signal level. This
produces a smoother sound that tends to retain dynamic character, but
the tradeoff is that the 3630 cannot react as rapidly to sudden level shifts.
Examples: Setting a longer attack time with guitar allows more of the pick
attack to come through. A longer attack time with kick drum lets through
more of the beater "thock." For recording, you may want to trade off
response time for smoothness. When used to prevent loudspeaker or
power amp clipping, a fast attack time is desirable.
Release (50 ms to 3 seconds)
This control works only with the Peak/RMS switch (section 1.5) in Peak
mode. RMS mode automatically adjusts the release time, depending on
the characteristics of the signals being processed.
In peak mode, this control determines how long it takes for the limiter to
return to unity gain after going into limiting. With short release times, the
limiter tracks every little change in level, producing a potentially uneven
or "rippling" effect that decreases dynamics but increases the average
output level. Longer release times tend to "squash" the signal more,
producing less overall output but retaining more of the signal's dynamics.
Excessive release times can be used as an effect. In the 60s using lots of
limiting with long release time on drums was a popular recording
technique.
Output (-20 to +20 dB)
The process of reducing dynamics lowers the signal's overall level. Use
this control to compensate by adding output gain.
Example: Limiting a signal by 6 dB will make the signal seem
approximately 6 dB softer. Compensate by using this control to increase
the level.

7
1.5 FRONT PANEL
COMPRESSOR/LIMITER SWITCHES
Each switch has an in and out position. The legend above each switch
shows which status is associated with which switch position.
Peak - RMS
With peak response, the 3630 responds to signal peaks to insure that these
peaks do not exceed a particular threshold. This mode is ideal when using
the 3630 to avoid clipping, a phenomenon when signal peaks exceed a
particular device's headroom. In RMS mode, the 3630 responds to a
signal's average level. This preserves more of the relationship between a
signal's peaks and valleys, and is useful when you want to compress or
limit but still retain a fair amount of dynamic feel.
Note: in RMS mode, the attack and release times will be program de-
pendent. The front panel attack and release controls will have no effect on
the signal.
Hard knee - Soft knee
With hard knee response, signals are clamped to the limiting threshold as
soon as they exceed it. With soft knee response, signals are clamped more
gently, giving a more natural sound.
Input - Output
Selects whether the input/output meter displays the input signal or
output signal. See section 1.7, Front Panel Metering, for more information.
Bypass - Comp
In the bypass position (the gain reduction LEDs will turn off), the limiter
circuitry is switched out of the signal path so you can hear the un-
processed sound. In the Comp position, the 3630 processes the input
signal.
Note: The 3630 must be powered up to pass a signal with either switch
setting.
Stereo Link Switch
In stereo operation, both channels need to operate in a complementary
fashion to avoid shifting the stereo image as one channel or the other
goes into limiting. With the Link switch out, Channels A and B operate
independently as two monophonic compressor/limiters.
8
With the Link switch in, Channel A's controls become master controls for
Channels A and B, with the exception of the input/output and the +4
dBu/-10 dBV switches which will continue to operate independently. The
stereo signal is processed identically by both channels to preserve proper
stereo imaging.
While in stereo mode, the compressor and gate control signals are derived
from a combination of Channel A and Channel B inputs. Compression
and gating are not soley dependent upon the input signal present at
Channel A (the master channel). For example, an input signal on either
Channel A or Channel B will cause compression to occur (and/or open
both gates) once it rises above the threshold set by Channel A controls,
even if there is no input signal present on the opposite channel.
For stereo sidechain applications, please refer to Section 1.8.
1.6 FRONT PANEL
NOISE GATE CONTROLS
The noise gate will not pass signals below the specified threshold setting,
but signals above the threshold will pass unaffected. In a typical
application, the threshold would be set just above any residual hiss or
noise. Thus with no signal going through the 3630, no hiss would be
audible. A signal going through the 3630 would pass through unimpeded.
The hiss would also be present under these conditions, but since a strong
signal is present it would tend to "mask" the hiss.
To use the 3630 solely as a noise gate, set the Ratio control to 1:1. This
passes the input signal to the noise gate without processing.
Threshold (no gating to -10dBV)
Sets the level above which the noise gate will allow signals to pass.
Turning the Threshold fully counter-clockwise disables the noise gate and
lets the signal through unaltered.
To set the proper gate level for most applications, turn the Gate Threshold
to OFF. Turn on all instruments to be gated but do not pass program
material through them (For example, turn your microphone on but do
not sing through it). Increase the Threshold (clockwise) until the red
CLOSE LED comes on. Any background noise should now be eliminated.

7
1.5 FRONT PANEL
COMPRESSOR/LIMITER SWITCHES
Each switch has an in and out position. The legend above each switch
shows which status is associated with which switch position.
Peak - RMS
With peak response, the 3630 responds to signal peaks to insure that these
peaks do not exceed a particular threshold. This mode is ideal when using
the 3630 to avoid clipping, a phenomenon when signal peaks exceed a
particular device's headroom. In RMS mode, the 3630 responds to a
signal's average level. This preserves more of the relationship between a
signal's peaks and valleys, and is useful when you want to compress or
limit but still retain a fair amount of dynamic feel.
Note: in RMS mode, the attack and release times will be program de-
pendent. The front panel attack and release controls will have no effect on
the signal.
Hard knee - Soft knee
With hard knee response, signals are clamped to the limiting threshold as
soon as they exceed it. With soft knee response, signals are clamped more
gently, giving a more natural sound.
Input - Output
Selects whether the input/output meter displays the input signal or
output signal. See section 1.7, Front Panel Metering, for more information.
Bypass - Comp
In the bypass position (the gain reduction LEDs will turn off), the limiter
circuitry is switched out of the signal path so you can hear the un-
processed sound. In the Comp position, the 3630 processes the input
signal.
Note: The 3630 must be powered up to pass a signal with either switch
setting.
Stereo Link Switch
In stereo operation, both channels need to operate in a complementary
fashion to avoid shifting the stereo image as one channel or the other
goes into limiting. With the Link switch out, Channels A and B operate
independently as two monophonic compressor/limiters.
8
With the Link switch in, Channel A's controls become master controls for
Channels A and B, with the exception of the input/output and the +4
dBu/-10 dBV switches which will continue to operate independently. The
stereo signal is processed identically by both channels to preserve proper
stereo imaging.
While in stereo mode, the compressor and gate control signals are derived
from a combination of Channel A and Channel B inputs. Compression
and gating are not soley dependent upon the input signal present at
Channel A (the master channel). For example, an input signal on either
Channel A or Channel B will cause compression to occur (and/or open
both gates) once it rises above the threshold set by Channel A controls,
even if there is no input signal present on the opposite channel.
For stereo sidechain applications, please refer to Section 1.8.
1.6 FRONT PANEL
NOISE GATE CONTROLS
The noise gate will not pass signals below the specified threshold setting,
but signals above the threshold will pass unaffected. In a typical
application, the threshold would be set just above any residual hiss or
noise. Thus with no signal going through the 3630, no hiss would be
audible. A signal going through the 3630 would pass through unimpeded.
The hiss would also be present under these conditions, but since a strong
signal is present it would tend to "mask" the hiss.
To use the 3630 solely as a noise gate, set the Ratio control to 1:1. This
passes the input signal to the noise gate without processing.
Threshold (no gating to -10dBV)
Sets the level above which the noise gate will allow signals to pass.
Turning the Threshold fully counter-clockwise disables the noise gate and
lets the signal through unaltered.
To set the proper gate level for most applications, turn the Gate Threshold
to OFF. Turn on all instruments to be gated but do not pass program
material through them (For example, turn your microphone on but do
not sing through it). Increase the Threshold (clockwise) until the red
CLOSE LED comes on. Any background noise should now be eliminated.

9
Example: To remove hiss from a guitar amp signal, set the Threshold just
above the residual hiss while muting the guitar strings. Playing guitar
should produce a signal higher than the threshold, letting through the
notes. When the guitar is not playing, the residual hiss signal should be
below the threshold, closing the gate.
Rate (20 ms to 2 seconds)
When a signal dips below the threshold, Rate determines how long it
takes for the gate to fade smoothly from the gate open to gate closed set-
ting. Shorter settings provide maximum hiss reduction but tend to create
a "choppier" sound. Longer settings gain a smoother response at the
expense of possibly letting a little hiss come through after the input signal
dips below the threshold.
1.7 FRONT PANEL METERING
The 3630's three meters for each channel indicate several important
parameters.
Gain Reduction Meter (-1 to -30 dB)
This compares the processed and unprocessed sounds, and shows the
amount of gain reduction being applied to the input signal.
Example: A meter reading of -6 dB indicates that the 3630 is attenuating the
input signal by at least 6 dB in order to keep it at the threshold level. The
more lights that are lit, the greater the amount of limiting, and the more
processed the sound.
Input/Output Meter (-30 to +6 dBu)
This monitors the input or output signal, as selected by the Input/Output
switch. This is useful when matching input and output levels, or to
compare the signal level prior to limiting with the signal level that occurs
after limiting.
10
Noise Gate Meter (Open or Closed)
When the noise gate is closed (i.e., the input signal is below the noise gate
threshold), the red Close LED is lit. When the noise gate is open and
letting through the input (i.e., the input signal is above the noise gate
threshold), the green Open LED is lit. The red Close LED fades from on to
off over the time set by the noise gate Rate control.
Since either the Open or Close LED will be on at all times, these also serve
as power-on indicators.
1.8 SIDE CHAIN APPLICATIONS
The side chain jack allows for two useful functions:
• "Keying" one signal with another, so that the dynamics of one signal
depend on the dynamics of a second signal
• Frequency-dependent limiting, so that limiting is triggered only by
certain frequencies.
The side chain jack is a stereo jack, where the ring connection sends the
3630's control signal for processing, and the tip connection receives the
processed sound. For keying applications, a regular mono cord can be
used since it is not necessary to send the 3630's control signal out for
processing. For frequency-dependent limiting applications that involve
plugging into another signal processor, a special stereo-to-dual-mono
cord is required, as shown below.
Mono send
to EQ (rin
g
)
Mono return
from EQ (ti
p
)
Stereo Insert
(to 3630 sidechain)
T
i
p
R
i
n
g
S
l
eeve

9
Example: To remove hiss from a guitar amp signal, set the Threshold just
above the residual hiss while muting the guitar strings. Playing guitar
should produce a signal higher than the threshold, letting through the
notes. When the guitar is not playing, the residual hiss signal should be
below the threshold, closing the gate.
Rate (20 ms to 2 seconds)
When a signal dips below the threshold, Rate determines how long it
takes for the gate to fade smoothly from the gate open to gate closed set-
ting. Shorter settings provide maximum hiss reduction but tend to create
a "choppier" sound. Longer settings gain a smoother response at the
expense of possibly letting a little hiss come through after the input signal
dips below the threshold.
1.7 FRONT PANEL METERING
The 3630's three meters for each channel indicate several important
parameters.
Gain Reduction Meter (-1 to -30 dB)
This compares the processed and unprocessed sounds, and shows the
amount of gain reduction being applied to the input signal.
Example: A meter reading of -6 dB indicates that the 3630 is attenuating the
input signal by at least 6 dB in order to keep it at the threshold level. The
more lights that are lit, the greater the amount of limiting, and the more
processed the sound.
Input/Output Meter (-30 to +6 dBu)
This monitors the input or output signal, as selected by the Input/Output
switch. This is useful when matching input and output levels, or to
compare the signal level prior to limiting with the signal level that occurs
after limiting.
10
Noise Gate Meter (Open or Closed)
When the noise gate is closed (i.e., the input signal is below the noise gate
threshold), the red Close LED is lit. When the noise gate is open and
letting through the input (i.e., the input signal is above the noise gate
threshold), the green Open LED is lit. The red Close LED fades from on to
off over the time set by the noise gate Rate control.
Since either the Open or Close LED will be on at all times, these also serve
as power-on indicators.
1.8 SIDE CHAIN APPLICATIONS
The side chain jack allows for two useful functions:
• "Keying" one signal with another, so that the dynamics of one signal
depend on the dynamics of a second signal
• Frequency-dependent limiting, so that limiting is triggered only by
certain frequencies.
The side chain jack is a stereo jack, where the ring connection sends the
3630's control signal for processing, and the tip connection receives the
processed sound. For keying applications, a regular mono cord can be
used since it is not necessary to send the 3630's control signal out for
processing. For frequency-dependent limiting applications that involve
plugging into another signal processor, a special stereo-to-dual-mono
cord is required, as shown below.
Mono send
to EQ (rin
g
)
Mono return
from EQ (ti
p
)
Stereo Insert
(to 3630 sidechain)
T
i
p
R
i
n
g
S
l
eeve

11
Keying Application: Ducking
A typical use of keying is to lower background music in the presence of
narration. This is called ducking because the music "ducks" to get out of the
way of the narration. A similar application would be to lower the level of
a rhythm guitar while a vocalist is singing. To perform ducking:
1. Process the signal to be "ducked" (e.g., background music) through the
3630. For stereo signals use both channels, for mono signals just use
one channel.
2. Plug the control signal (e.g., narration) into the channel's side chain jack,
using a cord with a mono 1/4" phone plug.
3. The Threshold, Ratio, Attack, and Release controls now affect how
much ducking will occur in response to the control signal. The Gain
Reduction meter will show how much the "ducked" signal is being at-
tenuated by the control signal.
Note: For stereo ducking using a single control source, the control source
may be inserted into either side chain input. An unconnected 1/4" plug
(stereo or mono) must be inserted into the other side chain input in order
to disconnect the program material of that channel from the
compressor/gate control circuitry.
Vo
i
ce us
i
ng
sidechain
jack as
trigger input
Bac
k
groun
d
mus
i
c
Bac
k
groun
d
mus
i
c
(li
m
i
te
d
and ready to be mixed
with the lead instrument)
Ducking. The signal at the sidechain's input (lead
instrument or vocal) triggers the 3630, causing the
stereo signal present at the inputs (background
music) to be limited only when the lead instrument
or vocal is
p
resent
Mono or
Stereo
p
lu
g
To m
i
xer
f
or
monitoring
12
Frequency-Dependent Limiting Application: De-Essing
Some vocalists and announcers, especially if equalized for more treble,
will produce excessive "sibilance" ("S" sounds, concentrated mostly in the
upper midrange and treble). In this situation, the limiter would ideally
limit the signal only when high frequency "S" sounds occur. This is
possible by inserting an equalizer into the side chain jack.
This application requires the special stereo-to-dual-mono cord mentioned
above and an equalizer, such as the Alesis MEQ 230.
1. Plug the cord's stereo plug into the 3630's side chain jack.
2. Plug the stereo cord's ring plug into the EQ's input.
3. Plug the stereo cord's tip plug into the EQ's output.
4. Increase the EQ gain in those bands whose frequencies should trigger
limiting of the signal. For de-essing applications, try equalizer frequen-
cies in the range of 2 kHz to 10 kHz. Setup for de-essing is quite easy.
With a graphic equalizer, select a frequency (2K for example), and set
up an excessive boost (as much as 12dB). If the chosen frequency is cor-
rect, the excessive gain at that frequency will trigger the compressor
when overly sibilant passages occur. If you are successful, try adjacent
frequencies one at a time to see which frequency gives the best results.
With a parametric EQ, create an excessive boost in the 2kHz - 10kHz
band, and sweep the frequency control until best results are obtained.
Thus, the high frequency "S" sounds trigger program limiting more
readily than the non-"S" sounds.
5. Adjust the Threshold, Ratio, Attack, Release, etc. for the desired degree
of high-frequency limiting. In de-essing applications, it is your goal to
set the attack and release times as fast as possible, so that the sibilant
peaks are eliminated without any audible change in the program
material.
EQ
i
nserte
d
i
nto
3630's sidechain
Vocal
T
o tape
Frequency Dependent Limiting (Stereo De-essing).
The EQ inserted into the 3630's sidechain insert
allows excessive sibilance to be limited without
affectin
g
the rest of the
p
ro
g
ram content
T
o tape
Mono or
Stereo
p
lu
g
V
oca
l