Sebatron Smac User manual

S
tereo
M
usical
A
udio
C
ompressor
(C) Sebatron 2012
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SMAC
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SMAC

Table of Contents:
SMAC
1/introduction
2/features
3/controls
4/operation
5/input/output
6/specifications
(C) Sebatron 2012

1/introduction
SMAC is a Stereo Musical Audio Compressor (or two channel mono)
that uses optical gain reduction cells (two per channel or ‘dual-servo’) to
perform quality transparent audio compression, peak limiting, and automatic
audio leveling control.
Due to the dual-servo optical based design, the dynamic behavioural
characteristics of SMAC lie somewhere between the classic Optical type
compressors and the later VCA type compressors. Depth, image, and sonics
are all preserved while the dynamics and transients of the signal can be
contoured and manipulated to suit any tracking, mixing, and/or mastering re-
quirements.
Compression can be fine tuned to be anything from ‘smooth and sub-
tle’ to ‘drastic and squashed’. SMAC has the ability to quickly and flawlessly
handle any compression application. Compression activity and amount are
totally variable. The Class-A make-up gain stage is transparent and provides
ample gain to offset heavy amounts of level reduction. This gives SMAC a
multitude of creative possibilities.
Extensive compression envelope flexibility is also provided via the
standard fully-variable attack and release dials, as well as an incorporated
envelope time factor control toggle switch called, ‘norm/tight/swim’. Each of
these innovative settings has a whole range of applications, from dealing with
fast transients (such as drums or percussion), to dealing with slower signals
(such as vocals or bass).
To facilitate stereo mix processing, two modes of stereo channel
linking are available: ‘dual-mono with channel one master’ and ‘stereo link’.
These modes are ideal for any stereo mix buss or sub-group compression re-
quirements where stereo spatial width needs to be harnessed and maintained.
SMAC also features two large VU style meters which can be
individually used to monitor output level or accurate gain reduction.
Utilizing solid-state topology, the SMAC audio path is completely
Class-A and discrete. For maximum headroom, all active components run on a
+60v rail. This gives SMAC a wide open sound that is tight and accurate. Like
all studio based Sebatron products currently available, there are no
integrated circuits (or ‘chips’) in the design.
Whether operating in high-end professional recording studios, home
recording setups, or live music venues, SMAC is designed to be the perfect
quality stereo compressor.
(C) Sebatron 2012

2/features
- fully-balanced (XLR) inputs and outputs
- dual-servo optical compression for increased
compression range, transparency, and smooth dynamic
response.
- accurate VU metering switchable from Output to
Gain Reduction
- fully-variable threshold, ratio, attack, and release
- 28dB clean output gain makeup
- ‘pump’ switch for high-ratio pumpin’ compression
- ‘swim’ switch for extra long attack and release
- two modes of stereo linking
- fully relay driven bypass
- external side-chain inputs/outputs for easy connection
of external EQ
- completely discrete, Class-A circuitry. No integrated
circuits or ‘chips’
- switchable mains voltage
- solid metal build
(C) Sebatron 2012

2/features
AUDIO PATH
The SMAC audio path was designed for maximum audio
transparency, leaving the emphasis on the processing time constants and
compression accuracy to perform the required duties. All circuitry is Class-
A operation with high voltages used throughout for an extended dynamic
range and tight bottom end. Internally, the circuit is designed around all
discrete, hi-quality, hi-voltage components, and is configured to be single
ended throughout. All active audio and processing circuitry runs on a +60v
rail for low noise, maximum headroom, fast transient response, and
wide bandwidth.
DYNAMIC AUDIO PROCESSING
The SMAC compression circuit uses two optical cells arranged
in dual-servo configuration. This means that along with the control volt-
age created by the detection circuitry, an inverse control voltage is also
generated by a D.C. phase splitter which controls an alternate optical cell
in complementary mode to the normal cell. This has many advantages
over the standard configuration of a single cell. For example, compression
depth is greatly increased, and the ballistics and distortions of the LED
light source are cancelled out by the complementary cell.
Being an ‘Optical’ audio compressor also means that the signal is
less coloured than some of the other popular compression methods such
as FET. Less signal is being attenuated by the cell in idle mode and
therefore requires less make up gain at the aft end. Less make up gain
means less noise, distortion, and other undesirable audio artifacts.
VU METERING
SMAC features accurate VU output level metering as well as
accurate gain reduction reading, or, in other words, the amount of
compression taking place at any given time.
Gain Reduction metering is driven in the same optical way as the
compression itself. This is an accurate representation of the amount of
compression taking place and is expressed in negative ‘dB’ on the VU me-
ter.
To monitor the input signal, simply switch SMAC into bypass and
select ‘output’ on the VU metering switch.
(C) Sebatron 2012