Aphex AURAL EXCITER III User manual

AURAL EXCITER® TYPE III
MODEL 250
OPERATING GUIDE
&
SERVICE MANUAL
APHEX SYSTEMS LTD.

WARNING
TO REDUCE THE RISKS OF FIRE OR ELECTRIC
SHOCK, DO NOT EXPOSE THIS APPLIANCE TO
RAIN OR MOISTURE

TABLE OF CONTENTS
1.0 INTRODUCTION 1-1
2.0 OPERATIONAL CHARACTERISTICS 2-1
2.1 New Features 2-1
2.2 Typical Applications 2-3
2.3 Specifications 2-4
2.4 Warranty and Service Information 2-6
3.0 INSTALLATION 3-1
3.1 Unpacking 3-1
3.2 Setting Input Sensitivity 3-1
3.3 Audio I/O (Input/Output) Connectors 3-1
3.4 I/O Connection Considerations 3-2
3.5 AC Line Connection 3-2
3.6 Remote Control Connection 3-4
3.7 Installing the Type III in an Equipment
Rack 3-4
3.8 Applying Power and Initial Checkout 3-5
4.0 FRONT PANEL CONTROLS 4-1
4.1 NR MODE Switch 4-2
4.2 NR THRESHOLD Switch 4-4
4.3 TUNE Control 4-5
4.4 PEAKING Control 4-4
4.5 NULL FILL Control 4-5
4.6 HARMONICS Control 4-6
4.7 TIMBRE Control 4-8
4.8 MIX Control 4-8
4.9 Ax Switch 4-8
4.10 SOLO Switch 4-9
4.11 SPR Switch 4-9
4.12 RELAY Switch 4-10
4.13 POWER Switch 4-10
5.0 APPLICATIONS 5-1
5.1 Initial Settings 5-1
5.2 Exciting a Recorded Tom or Kick Drum 5-3
5.3 Recording a Snare Drum with
Excitement 5-4
9310HTW
Table of Contents 1

TABLE OF CONTENTS
5.0 APPLICATIONS (continued)
5.4 Exciting FM Audio for Television
and Radio 5-5
5.5 Exciting AM Broadcast Audio 5-6
5.6 User Templates 5-7
6.0 CIRCUIT DESCRIPTION 6-1
6.1 Main Audio Path 6-2
6.2 Ax Sidechain Path 6-5
6.3 Power Supply 6-7
7.0 TEST AND NULLING PROCEDURES 7-1
7.1 Main Audio Board 7-1
7.2 Control Boards 7-2
8.0 PARTS LIST 8-1
8.1 Main Audio Board 8-1
8.2 Control Board 8-5
8.3 Power Supply 8-8
9.0 SCHEMATICS
2Table of Contents

1.0 INTRODUCTION
A little history...
The new Aural Exciter III
It all started back in 1956 when Curt Knoppel, an inventor and entrepreneur
who was tinkering with a Heathkit amplifier, accidentally stumbled across
the principles behind a new audio processor that could effectively restore the
essential high-frequency musical harmonics that are lost in the recording and
playback process. Nineteen years later, after moving to the United States
from Sweden, Knoppel met Marvin Caesar, then an accountant and land
developer. An audiophile himself, Caesar marvelled at Knoppel's invention,
and the two became partners in 1975, forming Aphex Systems in Framing
ham, Massachusetts.
After moving to Hollywood, California in 1976, the company began to
establish itself by leasing its provocatively-named "Aphex Aural Exciter" to
record companies for $30 per minute of finished product. The original
Model 402 was tube-powered and was subsequently updated to a solid state
version, the Model 602. This two-channel unit provided controls for input
sensitivity, output level, Aphex mix, de-esser, and signal phase reversal.
The unique combination of circuitry made this psychoacoustic processor an
essential ingredient in producing the "California" sound on numerous
projects, including albums by Heetwood Mac, Linda Ronstadt, James Taylor,
and Jackson Brown. As the hit list grew, so did criticism from detractors,
and, more importantly, competition from manufacturers with knock-off
products.
In 1982, in an effort to stay innovative and also keep ahead of the field,
Aphex introduced the second generation Model 201, the Aphex Aural Exciter
II. This version provided additional features for tuning the high pass filter,
as well as controlling the range and type of harmonics generated within the
patented Aphex process. Also, the VU meters were replaced with electronic
bar graph indicators having selectable ballistics and reference level settings.
This new design was a great advancement over the aging Model 602, yet the
biggest change was the dropping the policy of lease only in favor of outright
purchase. Popularity soared as numerous engineers and producers found
out that they could now buy the famous Aphex Aural Exciter. The increased
sales volume propelled the Model 201 into every conceivable sound applica
tion. It seemed as though every sound specialist was using the Aural
Exciter II in recording studios, concert venues, film dubbing theaters,
broadcast, and video post-production houses throughout the world.
The beginning of 1989 marks the introduction of the latest generation Aphex
Aural Exciter III. The slimmer and more powerful Model 250 is the latest
successor to the premium product in the field of Aural Excitement. As you
read the following sections you will find information on Operational Char
acteristics, Installation, Front Panel Controls, Applications, Circuit Theory,
and Maintenance Procedures. Technicians and other interested users will
find complete schematics located at the end of the manual.
Introduction 1-1

2.0 OPERATIONAL CHARACTERISTICS
Special features...
Main and Sidechain
audio paths
A and B noise
reduction
The Aphex Aural Exciter Type III, Model 250, is the latest generation, fully -
professional Aural Exciter, loaded with powerful new processing features
and improved circuitry. The dual-channel Type III adds thrilling new
dimensions to Aural Excitement. Noise and distortion are virtually elimi
nated in the Type III circuitry, with new special features that make enhance
ment possible and actually erase noise from noisy sources. The Model 250 is
the third successor to the original Aphex Aural Exciter that started an audio
revolution back in 1975.
2.1 N ew Features in the M odel 250
The Aphex Type III Aural Exciter utilizes a patented audio process that will
recreate and restore missing harmonics. These harmonics are musically and
dynamically related to the original sound. When added, they restore natural
brightness, clarity and presence, and can actually extend audio bandwidth.
These harmonics are so low in level, however, they add little power to the
signal. Unlike an equalizer or other "brightness enhancers," which can only
boost high frequencies, the Type III Aural Exciter extends the high frequen
cies. It is a single-ended process that can be applied at any point in an audio
chain, and needs no decoding.
2.1.1 Two Audio Paths
The Type III Aural Exciter process consists of two audio paths, the main path
and the process side-chain path. The main path transparently conveys the
audio signal directly from the input stage to the output stage, maintaining
unity gain with wide dynamic range. The side-chain path contains all of the
Aural Exciter processing circuits and receives audio from the input stage. A
mixing circuit in the main path allows the sidechain output signal to be
mixed with the main signal. You adjust the amount of MIX to set the
strength of the effect.
2.1.2 Two Noise Reduction Modes
Additional new design features include two modes of noise reduction. Mode
A and Mode B, for sound enhancement without adding to the noise floor of
reasonably noise free sources. It can also enhance the brightness, detail and
clarity of seriously noisy audio sources while, at the same time, erasing much
of the original noise.
Mode A operates as a linear sidechain expander with variable threshold. The
expansion ratio of 2.5-to-l permits the sidechain MIX to follow the signal
level below threshold. When the higher frequencies of the input signal
drop below threshold, the MIX will drop at a proportional 2.5 to-1 ratio. In
this way, the original signal-to-noise is not affected even with a great deal of
enhancement.
Operational Characteristics 2-1

Mode B is a revolutionary new noise reduction technique which operates to
actually "erase" source audio noise while the Type III enhances the signal.
This feature allows you to restore brightness and intelligibility to noisy
recorded tracks or other noisy sources and improve the signal-to-noise ratio!
Both modes are fast and easy to use, and effective in any application from
live sound to broadcasting and recording.
2.13 Spectral Phase Refractor (SPR)
Correct bass delay The SPR, or Spectral Phase Refractor, function of the Type III is a totally
new concept in psychoacoustic enhancement which can produce some
amazing results. Through the many steps of recording, duplicating, distrib
uting and reproducing sound, the phase of the low frequency audio spec
trum becomes delayed compared to mid and high frequencies. This is a
natural and unavoidable effect which becomes worse with each generation.
When the bass frequencies become delayed in time compared to other
sounds, the bass loses fullness and definition and seems to become less
powerful, even though there may be no actual loss of bass frequency re
sponse. The high end also loses definition, seeming to get duller.
Amplitude equalization at this point will not fully restore the clarity and bass
power. In fact, it may worsen the condition causing clipping or overload
distortion. SPR corrects the bass delay anomaly to restore clarity and
openness and significantly increases the apparent bass energy level without
adding any amplitude equalization or "bass boost. " The SPR function
works harmoniously with the new Aural Exciter circuitry to give the Type III
Aural Exciter amazing new capabilities.
2.1.4 Adjustable Harmonics Level and Timbre Mixing
The DRIVE Control of previous Aural Exciters has been eliminated. In its
place are two new controls that provide adjustable mixing of the exact
amount of desired harmonics level and timbre. These features make the
Type III more flexible and even easier to use.
2.13 Servo Balanced Inputs and Outputs
Short-circuit proof Although more costly than conventional designs, servo-balancing offers
many advantages. Servo-balanced input circuits absorb high common-mode
voltages found in long cable runs without sacrificing headroom. Servo-
balanced outputs are not only short-circuit proof, but can be used single-
ended at any time without the usual 6 dB loss of conventional circuits.
To use input or output in a single-ended (unbalanced) mode, you need only
to ground the unused pin. In addition, both inputs and outputs are fully RF
protected. The unity gain I/O structure is normalized for both+ 4 dBu
(professional) and -10 dBv (IHF) operating levels by switch selection from
the rear panel.
2-2 Operational Characteristics

2.1.6 Null Fill
Phase Nulling... NULL FILL is a new and useful tuning adjustment introduced for the first
time with the Aural Exdter Type III. The addition of NULL FILL to the
PEAKING and TUNE controls gives the Type III more power and flexibility
to enhance all types of audio sources. To understand how it works, it is nec
essary to understand a physical phenomenon called "Phase Nulling" which
occurs with all Aural Exciters when the MIX control is adjusted to obtain
high frequency enhancement.
There is a time delay associated with the sidechain signal which is an impor
tant part of the operating theory of the Aural Exciter. This time delay causes
transient waveforms to be slightly "stretched" as the sidechain signal is
added to the main audio path. The "stretched" transients are then perceived
by the ear as more pronounced or "louder". The side effect of the time delay
is a "dip" or "null" in the output equalization curve. The null can be a
desirable characteristic because it compensates for the slight additional
power added to the signal by the high frequency shelving boost. The null
de-emphasizes the frequency range around the TUNE control setting, thus
giving even greater emphasis to the higher frequencies.
There are times, however, when the Phase Null is unwanted. The NULL
FILL control allows the user to "fill-in" the phase null to any desired amount,
thus further improving presence.
2.2 Typical Applications
Operational Characteristics 2-3
The Aural Exciter may be used in many ways for audio enhancement.
Depending upon the requirements, either pre- or post-processing may be
selected. Either source or system optimization, or a combination of both, is
possible.
2.2.2 Sound Reinforcement
Increase intelligibility For example, a P.A. system may be greatly enhanced by using the Aural
Exciter to increase the intelligibility of the loudspeakers, thus improving
penetration of the sound around comers and in areas usually difficult to fill.
In another case, the source may sound dull and hard to understand. The
Aural Exciter will compensate for this deficiency by adding brightness and
clarity to the sound more effectively than use of equalization alone.

Pre-process recordings
Extend bandwidth
2.2.2 Tape Duplication
The Aural Exciter may be used to "pre-process" recordings to anticipate the
audio degradation in the medium or during subsequent reproduction. Much
of the detail added by the Aural Exciter will survive filtering and distortion
of the reproduction equipment and provide a better quality audio playback.
Audio and Video Cassette duplication are examples of this application.
Broadcasting is another good example.
2.23 Sound Recording
In the recording studio, post production suite or similar environment, post
processing of previously recorded sound tracks can restore lost vibrance and
realism, even to the extent of saving dialogue or sound effects which were
thought to be unusable. Instruments and vocals can be made to stand out in
the mix without substantially increasing the mix levels or using equalization.
2.2.4 Electronic Music
Many electronic instruments are limited by their sampling rate (bandwidth)
and word length (resolution); they can sound lifeless. The Aural Exciter
actually extends bandwidth and adds details making synthesizers, samplers
and drum machines come alive.
2.23 Broadcasting
Broadcast audio is constrained in dynamics and frequency response to fit the
parameters of AM and FM transmission. AM and FM radio, as well as tele
vision audio, all have unique, critical bandwidth and signal level transmis
sion limits. The Type III is especially useful in creating the perception of
higher frequencies and greater dynamics without pre-emphasis distortion or
overmodulation. As a result, the final audio product has more presence and
clarity, with no apparent increase in noise.
2.3 Specifications
2-4 Operational Characteristics
VCA: A phex1001
Frequency Response: +0,-ldB from lH z to 190 kHz
THD: .01% Max@ +27dBu
IMD: .01 % Max @ + 27 dBu
Max Input/Output Level: +27 dBu
Nominal Gain: 0 dBu

InputInpedance: 19.5 k Ohms/600 Ohms (switch selectable
from rear panel)
Load Impedance: 600 Ohms or greater
Output Impedance: 65 Ohms
Unweighted Output Noise (20
Hz-20 kHz BANDWIDTH):
-86 dBu
Unweighted SNR(for +4dBu
operating level):
-90 dB
Dynamic Range: 114dB
Crosstalk: Better than 85 dB up to 20 kHz
Output Circuits: Servo Balanced Transformerless
Input Circuits: Servo Balanced Transformerless
Input CMRR: Better than 50 dB 20 Hz to 10 kHz
Input RF Rejection: Better than 40 dB at 800 kHz, better than 60
dB above 2 MHz
Power Requirements: 100/120/220/240VAC (+/- 10%), 50/60 Hz
16 W.
Size: 1 3/4" (44.5 mm) h x 19" (482.6 mm) wx9"
(228.6 mm) d
Weight: 8 lbs (s.63 kg)
Accessories: Model 51 Plexiglass Security Cover
Aphex Aural Exdter covered by U.S. Patent Number 4,150,253. Additional
Patents Pending. Foreign Patents granted and pending.
Aphex Systems is constantly striving to maintain the highest professional
standards. As a result of these efforts, modifications may be made from
time to time to existing products without prior notice. Specifications and
appearance may differ from those listed or shown. Aphex and Aural Exciter
are registered trademarks of Aphex Systems, Ltd.
Operational Characteristics 2-5