Videoquip AM-4 User manual

AM-4
Audio Monitor
Videoquip Research Limited
595 Middlefield Road, Unit #4
Scarborough, Ontario, Canada. MIV 3S2
[phone]
1-888-293-1071
www.videoquip.com

AM-4
4 channel
Analog, AES3 Digital, SDI Embedded Digital
Audio Monitor
User Manual
Introduction
The AM-4 is a DSP based digital audio signal monitoring unit, with facilities for monitoring two
Stereo Analog, two AES3 Stereo Digital, and two SDI Embedded stereo signal sources.
The four (two stereo channel) audio level meters display VU and PPM values simultaneously, with
dBu and dBFS scales.
Two stereo audio signals (Analog, AES3 digital, SDI embedded digital) may be monitored at a
time using the level meters. Only one of the two selected stereo sources can be monitored via the
built-in speakers, or with headphones.
The AM-4 supports four monitoring modes: Stereo, Left channel only, Right channel only, and Left
and Right summed mono.
A front panel volume control is provided, for use with speaker and headphone monitoring only.
The VU/PPM meters and Line output levels are not affected by the volume control.
The Analog inputs support either XLR or 1/4“ TRS connections. Analog input sensitivity is
adjustable for each individual input to either +4 dBm or –10 dBV nominal levels, by using the
internal jumpers provided on each analog input. AES3 Digital inputs are XLR-3F balanced, and the
SDI input is a BNC connection.
Two Analog outputs, two digital stereo line outputs, and a parallel GPI remote connection are
provided for convenience.
The Out-of-Phase LED will illuminate when phase reversal occurs on one of the stereo channels.
Note that this condition can occur not only for actual accidental phase errors, but may also appear
during segments where signal processing has been applied for sound imaging purposes.
A feature to test for an out-of-phase condition is provided. Pressing and holding down either A or B
pushbutton will reverse the phase of the right channel of the signal while it is being listened to.
This function is very useful to determine whether a stereo signal source is out-of-phase or not.
The Silence LED will illuminate when the signal level falls below the set threshold level, and stays
below the threshold for more than either 5 or 10 seconds in any one of the four channels currently
being monitored. The duration of silence and threshold level to activate this warning is determined
by the user-preset DIP switches.
In the SDI embedded digital audio signal, the carrier is divided into four groups, and each group
can contain up to two stereo digital audio signals. The AM-4 allows selection of one specific audio
group, and retrieval of one or both of the embedded stereo digital audio signals in that group.
Note: The AES3 digital and SDI Embedded digital audio interfaces are optional plug-in boards.

1. Functionality
1-1. Input Selection
Two stereo sources may be monitored simultaneously, one on the monitor A meters, and one on
the monitor B meters. The input source for each is selected using the Monitor Select and INPUT
pushbuttons. As an example, to monitor Analog input channel A, press the A pushbutton, then
select the Analog input source by pressing the INPUT pushbutton. When the INPUT pushbutton is
pressed, the input source selection will cycle through Analog, Digital AES3, and SDI digital, then
back to Analog. To assign a source to monitor B, use same process as described for A using the B
pushbutton.
Only input sources Analog-A, AES3 Digital-A and SDI channel 1 and 2 may be assigned to
monitor channel A. Only input sources Analog-B, AES3 Digital-B and SDI channel 3 and 4 may be
assigned to monitor channel B.
Monitored input sources are automatically routed to both the Analog and AES3 Digital line outputs.
Selecting one of four SDI groups is accomplished with the SDI pushbutton. Each SDI group
contains up to four (two stereo) digital audio channels.
The currently selected signal sources for monitor channels A and B are indicated by the LEDs
located above each VU meter pair.
The nominal sensitivity of all Analog line inputs is adjustable to either +4 dBm or –10 dBv by
jumper settings on the main circuit board.
1-2. Monitor source and Monitor Mode selection
Either monitor channel A or B can be selected and routed to built-in speakers by pressing the Aor
Bpushbutton.
Each depression of the monitor mode [ LEFT/RIGHT ] button selects one of 5 monitoring modes,
in sequence: (1) Stereo, (2) Left channel only, (3) Right channel only, (4) Monaural (5) Right
channel phase reversal ( out of phase ), then back to (1).
The LEFT and RIGHT LEDs indicate the current monitor mode:
(1) Stereo …………….… both LEFT and RIGHT LED are on.
(2) Left channel only …... only LEFT LED is on
(3) Right channel only … only RIGHT LED is on
(4) Monaural ………….… both LEFT and RIGHT LEDs flash once
(5) Right channel phase reversal … both LEFT and RIGHT LEDs flash twice.
Note that an Out-of-Phase condition listening test can be easily performed using mode 5.
The phase of the right channel will be reversed, allowing a comparative listening test to be
performed. This function is very useful when trying to determine whether a stereo signal source is
out-of-phase or not.
Speaker and/or headphone monitoring can be changed from normal Stereo mode to Left channel
only, Right channel only, or Left and Right summed mono mode by using the LR (Left Right)
pushbutton. Mono monitoring mode is indicated when both the L and R LEDs are flashing. Stereo
monitoring mode is indicated when both the L and R LEDs are continuously on.

1. Functionality (cont’d.)
1-3. VU / PPM Meter
The VU/PPM meters are 3 color LED bar displays, with 53 segments per channel.
By using a core DSP processor, all of the monitoring for the four (two stereo) signal channels are
processed in the digital domain for both RMS and PPM and calculated in real-time.
The VU and PPM values are then displayed in the range from –34 dBu ( -53 dBFS ) to +18 dBu ( 0
dBFS ) in 1 dB increments. All Analog signals are converted to the digital domain before being
processed by the DSP.
1-4. Out-of-Phase and Silence Monitoring
Out-of-Phase and Continuous Silence conditions for the selected audio sources are indicated by
the PHASE and A or B switch LEDs respectively. When an Out-of-Phase condition occurs on
monitor source A, the PHASE LED illuminates and the A switch flashes for the duration of the
condition.
A period of silence on a selected channel will illuminate the SILENCE LED for the duration of the
condition. The time period required to constitute a silence condition is selectable using the user-
preset DIP switches to be either 5 or 10 seconds. The Sensitivity threshold is adjustable to either –
36 dBFS or –48 dBFS.
1-5. Line output
Two stereo Analog line outputs, and optionally, two AES3 Digital outputs are provided. Digital line
outputs are mirror images of the Analog line outputs. The stereo source signals for the VU/PPM
meters are routed to these line outputs.
1-6. User presets
The internal user-preset DIP switch is located at the left-hand side near the power supply circuitry
on the main circuit board, and is designated as SW600. The eight switches provided for user-
presets are to define Silence duration, Silence threshold level, and Test tone mode.
Test tones with 0 VU (-18 dBFS) levels and frequencies of 400 Hz and 1 kHz can be generated
and routed to both the A and B line outputs when the TEST-TONE user preset switch is turned on.
The Silence duration and threshold level are both adjustable with the user preset switch for
convenience.
USER PRESET SWITCHES
1~ 5 Undefined
6 Test Tone
Off No test tone
On -18 dBFS , 400 Hz test tone routed to both A and B left output
channels, and 1 kHz test tone routed to both A and B right output channels.
7 Silence threshold level
On -36 dBFS
Off -48 dBFS
8Silence duration
Off 10 seconds
On 5 seconds

1. Functionality (cont’d.)
1-7. Monitor channel A & B independent Gain Control
The signal levels of the AM4 were originally designed with unity gain between any input
and any output. The signal levels for channel A & B can be increased or decreased up to
+30/–20 dB in 1 dB increments.
Increase or decrease gain
To increase / decrease gain, use combination of front panel control button [ A ] or [ B ], and
[ INPUT ] or [ SDI ] buttons. Button [ A ] or [ B ] selects the intended channel to change.
The [ INPUT ] button increases the gain and the [ SDI ] button decreases the gain.
For instance, to increase the gain of channel A, press and hold the [ A ] button, then press
[INPUT ] until the desired signal level is reached.
[ A ] or [ B ] to select channel …. A or B
[ INPUT ] gain increase. …… UP
[ SDI ] gain decrease. ……… DOWN
Gain display
Internal gains can be displayed on the VU meters. To see the current gain, press and hold
the [ A ] or [ B ] button for approximately a one-half second. The left channel VU meter
shows the amount of gain applied, relative to the right channel meter. The right channel
meter indicates the relative reference for unity gain. Each LED bar is equivalent to 1 dB.
(The reference level shown on the right channel VU is always at –30 dBFS. This –30 dBFS
reference was chosen for convenience only, in order to accommodate and display the gain
range of –20 to +30 dB.)
For instance when channel B’s gain is increased by +20 dB, the left channel gain display
shows the bar at –10 dBFS ( -30 + 20 = -10 ). The right channel’s VU bar is always at the
relative unity gain reference level, placed at -30 dBFS.
The factory default gain is 0 dB.

AM-4 Specifications
Power Requirements 115 VAC, 60 Hz or 230 VAC, 50 Hz, 50 W
Analog Audio Inputs
Input Impedance 20 kohms balanced, 10 kohms unbalanced
Nominal Input Level -10 dBV, or +4 dBu
Maximum Input Level +24 dBu
Input Connectors XLR-3F and 1/4"TRS, x 4
Common Mode Rejection -60 dB typical @ 60 Hz
Analog Audio Outputs
Output Impedance 100 ohms balanced
Output Signal Level +4 dBu nominal, +22 dBu maximum
Output Connectors XLR-3M, x 2
Digital Audio Inputs
AES3 XLR-3F x 2
SDI BNC
SDI Outputs BNC x 2, Active loop
VU/PPM Meters 3 Color, 53 Segment LED bar x 4
Attack Time 20.8 usec ( PPM )
Speakers 20 W, 8 ohms
Power Amplifier Outputs 15 W RMS, 8 Ohms
Frequency Response From 20 Hz to 20 kHz +/- 1 dB
THD + Noise 0.01% or less
Remote Control DB-9F; Parallel Remote (pull down to ground)
Physical Dimensions (Inches) 19 W x 3.5 H x 13 D, EIA rack mounting
Warranty
Videoquip Research Limited (VRL) warrants the AM-4 for a period of 2 (two) years from the date
of shipment from the factory, to be free of defects in workmanship and material under normal use
and service. This warranty is void if failure is due to abnormal use or modification, or if serial
numbers have been tampered with. VRL's liability is limited to the repair or replacement of this
unit, or to a sales credit, and the warranty action taken is at the sole discretion of VRL. Any
warranty claims must be received in writing by VRL before the expiration of the two year period.
Warranty coverage does not include shipping costs. This warranty is in lieu of all other warranties,
expressed or implied, and all other obligations or liabilities of Videoquip Research Limited.