CONTROL DESCRIPTIONS page 4OPERATION page 6 TECHNICAL SPECIFICATION page 8 h DRAWMER ELECTRONICS LTD. 1990 COPYRIGHT This manual is copyrighted ©… [610730]

DL231
OPERATORS MANUAL
CONTENTS
SAFETY CONSIDERATIONS page 1
INTRODUCTION page 2
INSTALLATION page 3
CONTROL DESCRIPTIONS page 4OPERATION page 6
TECHNICAL SPECIFICATION page 8
h
DRAWMER ELECTRONICS LTD. 1990

COPYRIGHT
This manual is copyrighted © 1990 by Drawmer Electronics, Ltd. With all rights
reserved. Under copyright laws, this manual may not be duplicated in whole or in partwithout the written consent of Drawmer.
ONE YEAR LIMITED WARRANTY
Drawmer Electronics Ltd., warrants the Drawmer DL231 audio processor to conform
substantially to the specifications of this manual for a period of one year from theoriginal date of purchase when used in accordance with the specifications detailedin this manual. In the case of a valid warranty claim, your sole and exclusive remedyand Drawmer’s entire liability under any theory of liability will be to, at Drawmer’sdiscretion, repair or replace the product without charge, or, if not possible, to refundthe purchase price to you. This warranty is not transferable. It applies only to theoriginal purchaser of the product.
For warranty service please call your local Drawmer dealer. Alternatively call
Drawmer Electronics Ltd. at +44 (0)1709 527574. Then ship the defective product,with transportation and insurance charges pre-paid, to Drawmer Electronics Ltd.,Coleman Street, Parkgate, Rotherham, S62 6EL UK. Write the RA number in largeletters in a prominent position on the shipping box. Enclose your name, address,telephone number, copy of the original sales invoice and a detailed description of theproblem. Drawmer will not accept responsibility for loss or damage during transit.
This warranty is void if the product has been damaged by misuse, modification or
unauthorised repair.
THIS WARRANTY IS IN LIEU OF ALL WARRANTIES, WHETHER ORAL OR
WRITTEN, EXPRESSED, IMPLIED OR STATUTORY. DRAWMER MAKES NOOTHER WARRANTY EITHER EXPRESS OR IMPLIED, INCLUDING, WITHOUTLIMITATION, ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FORA PARTICULAR PURPOSE, OR NON-INFRINGEMENT. PURCHASER’S SOLE ANDEXCLUSIVE REMEDY UNDER THIS WARRANTY SHALL BE REPAIR ORREPLACEMENT AS SPECIFIED HEREIN.
IN NO EVENT WILL DRAWMER ELECTRONICS LTD. BE LIABLE FOR ANY DIRECT,
INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES RESULTINGFROM ANY DEFECT IN THE PRODUCT, INCLUDING LOST PROFITS, DAMAGE TOPROPERTY, AND, TO THE EXTENT PERMITTED BY LAW, DAMAGE FORPERSONAL INJURY, EVEN IF DRAWMER HAS BEEN ADVISED OF THEPOSSIBILITY OF SUCH DAMAGES.
Some states and specific countries do not allow the exclusion of implied warranties
or limitations on how long an implied warranty may last, so the above limitations maynot apply to you. This warranty gives you specific legal rights. You may haveadditional rights that vary from state to state, and country to country.
In the interests of product development, Drawmer reserve the right to modify or
improve specifications of this product at any time, without prior notice.

DL231 OPERATORS MANUAL 1
DRAWMER DL231
Dual Expander Compressor Limiter
SAFETY CONSIDERATIONS
CAUTION – MAINS FUSE
TO REDUCE THE RISK OF FIRE REPLACE THE MAINS FUSE ONLY WITH
THE SAME TYPE, WHICH MUST BE A CLASS 3, 230 VOLT, TIME DELAY
TYPE, RATED AT 63mA WHERE THE MAINS INPUT VOLTAGE SWITCH IS
SET TO 230 VOLTS AC. AND 125mA WHERE THE MAINS INPUT VOLTAGE
IS 115 VOLTS AC.
ALL FUSES MUST COMPLY WITH IEC127-2.
THE FUSE BODY SIZE IS 20mm x 5mm.
CAUTION – MAINS CABLE
DO NOT ATTEMPT TO CHANGE OR TAMPER WITH THE SUPPLIED MAINS
CABLE.
CAUTION – SERVICING
DO NOT PERFORM ANY SERVICING. REFER ALL SERVICING TO
QUALIFIED SERVICE PERSONNEL.
WARNING
TO REDUCE THE RISK OF FIRE OR ELECTRIC SHOCK DO NOT EXPOSE
THIS EQUIPMENT TO RAIN OR MOISTURE.

DL231 OPERATORS MANUAL 2
INTRODUCTION
A compressor is a device which automatically controls the level of an incoming signal to
provide a more constant output.
Even in a digital system, which has a large dynamic range, compression is necessary on
some instruments and even on a final mix because the environment in which mostmaterial is heard is often noisy, to say nothing of the limited dynamic range of thereproduction equipment, e.g. portable radios and cassette players.
A well designed compressor should operate smoothly and create a minimum of distortion
and noise. Such a device in use should go almost un-noticed (unless for special effects)and require a minimum of adjustment.
A limiter is essentially the same as a comp ressor but as its name implies, it serves to
prevent the output from rising any higher than a pre-determined level.
The use of compression effectively raises low level signals, but this includes any ambient
noise. For instance, vocals usually require compression, but noise from headphones,together with the taking of breath, can be a problem for the engineer. This can beovercome by the use of an expander, which will attenuate signals below a preset level,
i.e. the opposite of compression.
A device which performs which performs all three functions gives all the benefits of
compression and limiting without the unwanted side effects. Additional refinements cangreatly increase the versatility of such a unit by automating some of the more criticalcontrol functions.
The DL231 is a dual channel Expander/ Compressor/Limiter combining ease of operation
with flexible performance. Each channel consists of a compressor, having variablethreshold, ratio, attack, release, and output gain controls; a peak limiter, which isrequired to prevent momentary overload when using gentle compression slopes and / orslow attack times and an expander / gate for the removal of unwanted ambient noisewhich would otherwise be ‘pumped up’ by the use of compression.
Although each channel is completely independent, linking is easily accomplished, which
prevents image shifting when treating stereo material.
Particularly attractive features are the unique dual function displays using Tri-colour
LED’s, which measure input signal levels, or gain reduction.
Both expander and compressor release are semi-automatic, programme related and are
adjustable via a single release control thus providing smooth operation and reducingsetting up time.
The expander section is equipped with fully automatic attack, which continuously adjusts
itself to match the rising envelope of the incoming signal. This feature is of enormousbenefit on vocals, because they contain ever changing transient characteristic, whichmakes manual adjustment difficult and time consuming, with sometimes doubtful results.
Equalisation may be applied to the compressor side-chain insert points. This allows
frequency conscious compression to be achieved. ‘Side chain listen’ facilities areprovided to allow both side-chains to be monitored.

DL231 OPERATORS MANUAL 3
INSTALLATION
The DL231 is designed for standard 19" rack mounting and occupies 1U of rack space.
Avoid mounting the unit directly above power amplifiers or power supplies that radiatesignificant amounts of heat. Fibre or plastic washers may be used to prevent the frontpanel becoming marked by the mounting bolts.
AUDIO CONNECTIONS
INPUTS and OUTPUTS: Both the input and output XLRs may be used either balanced
or unbalanced, the wiring convention being: pin 1 Ground,pin 2 Hot and pin 3 Cold. For use with unbalanced systems,the Cold pin (3) must be grounded at both input and outputXLRs.
If earth loop hum problems are encountered, don't
disconnect the mains earth but instead, try disconnecting thesignal screen on the cables connecting the DL221 to thepatchbay. If such measures are necessary, balancedoperation is recommended.
S/C INSERT: The side-chain insert point is configured as a stereo jack
socket wired tip return, ring send. This point is unbalancedand would normally be connected to a normalised or semi-normalised pair of patchbay contacts.
If earth loop problems are encountered, do not disconnect
the mains earth but instead, try disconnecting the outputsignal screen at one end of the cables connecting the DL221to the patchbay. If such meas ures are necessary, balanced
operation is recommended.
POWER CONNECTION
The unit will have been supplied with a power cable suitable for domestic power outlets
in your country. For your own safety it is important that you use this cable. The unitshould always be connected to the mains supply earth using this cable

DL231 OPERATORS MANUAL 4
CONTROL DESCRIPTION
Both channels of the DL231 are identical and may be used completely independently or
linked for stereo operation. In the linked mode, only the left hand channel controls arefunctional and serve as master controls, though the channel bypass switches remainindependent. In linked mode, the compressor / limiters and peak limiters and expandersof the two channels track together to avoid the inevitable image shifting that occurs if thetwo channels of a stereo signal are treated independently.
COMPRESSOR
THRESHOLD (Variable -24 dB to infinity) sets the point at which gain reduction
commences. Signals below threshold pass un-attenuated.NB ‘Threshold’ controls the signal level entering the side-chain andnot the input signal level. This can usually be adjusted on precedingequipment.
RATIO is variable between 1:1 (zero compression) 20:1 (limit).ATTACK (50µS to 5mS) controls the speed at which the compressor
responds to a rise in input signal level. A slow attack time will allowtransient peaks to escape compression, which can give an artificialpercussion effect on certain signals, whilst the fastest attack timeof 50 µS allows the compressor to respond to the fastest of audiosignals.
RELEASE (50mS to 5sec) is the time taken for the compressor to recover from
gain reduction. Programme signals are complex, so a complexrelease characteristic is required for optimum results. Fasttransients require a fast release time to avoid over limiting effects,whereas normal programme material should be user adjustable. Inaddition to these features, the DL231 contains circuits whichprevent partial recovery between waveform peaks, thus almosteliminating low frequency distortion when using fast release times.
OUTPUT GAIN (-20dB to +20dB) is necessary to make up signal level which is lost
during compression.
OUTPUT SWITCH enables the operator to select ‘normal’ or ‘bypass’ for comparison
of input or output levels or ‘S/C listen’ for monitoring anyequalisation which may be applied to the side-chain. EQ. applied inthis way enables frequency conscious compression to be achieved -particularly useful for de-essing, de-popping etc.
PEAK LIMITER a separate switchable peak limiter, connected after the output gain
control, complements the operation of the compressor section byallowing slow attack times and/or gentle compression slopes to be
used, whilst giving complete protection from overload. The limiterhas an internally preset threshold of +6dB (ref +4dB), fast attack (50µS) automatic release based on programme content and a ratio of50:1. Gain reduction from limiting is indicated on the display along
with compression, but in addition a LED located beneath the limitswitch indicates the onset of limiting.

DL231 OPERATORS MANUAL 5
LED BAR DISPLAY is a dual function facility which measures output level (input level if
bypass is selected) or gain-reduction, selectable by the displayswitch.
NB
i. The VU meter and threshold controls are calibrated to show 0VU at +4dBii. In the gain reduction mode, all the red LE D’s are very slightly illuminated at all
times. This is quite normal and does not indicate a fault condition.
EXPANDER
THRESHOLD (+10 to -40 dB) sets the point at which gain reduction takes place.
Signals above threshold pass un-attenuated unless compressionoccurs..
RATIO A three position switch selects ratios of 1:2, 1:5 or 1:20 provides
gating characteristics. Gating can be regarded as the opposite oflimiting.
ATTENUATION (Attn) a three position switch sets the maximum attenuation of 10,
20 or 40dB.
FUNCTION selects ‘side-chain listen’, normal (expander in operation) and off
(expander bypassed).
ATTACK time is completely automatic. See introduction.RELEASE time is semi-automatic, matched to the compressor release and is
adjustable via the compressor release
VISUAL DISPLAY is by means of three LED’s arranged in a horizontal ‘traffic light’
configuration. Green indicates zero expansion, whilst yellow showsgain reduction of 50%, referring to the attenuated setting and red100%.
STEREO LINK couples the control circuits of both compressors to prevent image
shifting when treating stereo material on a final mix. The peaklimiters can also be used if desired but they remain independent.Operational controls should be set the same on both channels whenlinked.
SIDE-CHAIN EQ may be applied to expanders and compressors via insert points at
the rear of the unit. Connection are via stereo jack ( Rind – send. Tip- return)

DL231 OPERATORS MANUAL 6
OPERATION
Having connected signal inputs and outputs as required, set the unit as follows-
Threshold, Ratio, Attack, Release – Anti clockwise
Output Gain – 0 dBDisplay Switch – VUOutput Switch – BypassPeak Limit – OffStereo Link – OffDisplay – VUExpander – Off
1. Adjust input signal level on preceding equipment to show 0 dB on display, peaking
to +2.
2. Change output switch to ‘norm’ and display switch to GR. Adjust Threshold, Ratio,
Attack and Release to give the required compression characteristics and read thegain reduction on the display.
3. Change output switch to VU and adjust output gain for optimum reading on the
display.
4. If the Peak Limiter is required, adjust output gain so that the limiter operates on
signal peaks only. It is important to remember that the peak limiter is connectedafter the output gain control so care should be taken to avoid ‘pushing’ the gaincontrols for more level, particularly when treating stereo signals.
5. For stereo operation, switch in the stereo link and set up as above, making sure
that all controls are the same for both channels. GR. displays will show the samereadings, except when excessive peak limiting occurs on either channel.
6. If ambient noise is ‘pumped’ up to an unacceptable degree during compression,
change expander switch to ‘norm’ and adjus t the expander threshold so that the
noise is removed. The expander threshold should be set below the compressorthreshold level to avoid interaction.
7. Set ratio and attenuation to suit the particular application. When used on a final
mix, set threshold as low as possible but above unwanted noise. Ratio should be1:2 and attenuation at 10 to 20 dB. This will provide a gentle expansion which willminimise drop out effects during a fade. However, drums would be better with a1:5 or 1:20 ratio and 20 or 40 dB attenuation using a higher threshold level. Forvocals, set threshold so as to re move breath and headphone noise and set ratio
a 1:2 or 1:5 with attenuation of 20 or 40 dB.In all cases, attack is automatic and release is controlled by the compressor.
These suggestions are for guidance only. The final adjustments should be made
to suit the particular application and conditions.

DL231 OPERATORS MANUAL 7
Using the Expander alone
Disable the compressor by turning either the threshold or ratio anti-clockwise. Adjust the
expander as described above but use compressor release control to adjust release time.An in-built ‘hold’ facility stabilises the expander against momentary gain reduction duringshort duration decreases in the signal level.
Frequency Conscious Expansion
This is used when unwanted noise at different frequencies to that being processedrequires removal without effecting the required signal. For example, some guitarflangers, treble boosters and amplifiers emit noise at higher frequency than that beingprocessed. Set the external equalisation by switching to ‘S/C listen’ and adjust to cut theoffending frequencies. The expander will then only operate on the required signal (thespill from a nearby bass drum or bass guitar c an be filtered in the same way). Switch to
‘norm’ and adjust the expander to obtain the required noise reduction.
NB The external filter will not affect the processed signal, only the control circuitry.
Frequency Conscious Compression
This can be achieved by applying EQ to the compressor side-chain access at the rear of
the unit. Once again, a ‘side chain listen’ facility is provided to assist this operation. Setthe equalisation so as to boost the offending frequencies. Switching to ‘norm andadjusting the compressor as necessary will result in the offending frequencies beingattenuated, but only when they exceed the threshold level. This method allowsbroadband HF boost above 2 kHz to be applied to the signal before compression thusobtaining a crisp, sharp sound. The sibilants thus created can be controlled withoutaffecting the basic tonal structure by boosting the side chain EQ at 7 to 10 KHz by 10 dBor so. By the same token, ‘popping’ caused by LF boost can be controlled by applyingboost to the side chain at frequencies below 100 Hz. For best results, a parametric orgraphic equaliser should be employed because offending frequencies often occupynarrow bands.

DL231 OPERATORS MANUAL 8
TECHNICAL SPECIFICATIONS
(Measurements taken at +4dBu operating level where applicable)
INPUT IMPEDANCE 20KOhm
BANDWIDTH 20Hz – 22KHz (1dB)
MAXIMUM OUTPUT LEVEL +24dBm (Electronic – floating)
+22dBm (Unbalanced)
SIDE CHAIN Send/Return Unbal, in phase input pin 2.
NOISE @ UNITY GAIN (Referred to +4dBm) Expander off.
Wideband !83dB
22Hz-22KHz !90dB
CCIR ARM !91dB
IEC A !94dB
Q. Pk CCIR !80dB
DISTORTION 100Hz 1KHz 10KHz
Unity gain +4dBm Input 0.025% 0.025% 0.025%
+14dBm input 10dB GR. 0.03% 0.03% 0.06%
COMPRESSOR
Threshold -24dB to infinity (ref +4dBm)
Ratio Variable 1:1 to 20:1Attack 50µS to 5mSRelease 50mS to 5 SecOutput Gain -20dB to +20dB
EXPANDER
Threshold -40dB to +10dB
Ratio 1:1, 1:2, 1:20 SwitchableAttenuation (Attn) 10, 20 or 40dB SwitchableAttack Fully automatic 50µS to 10mSRelease Related to compressor release and
programme content.
PEAK LIMITER
Threshold +6dB (ref +4dB)
Ratio 50:1Attack 50µSRelease Automatic
STEREO TRACKING within 1dB to 20dB GR.
within 3dB to 40dB GR.
POWER REQUIREMENTS 115Volt or 230Volt at 50-60Hz, 9 Watts
FUSE RATING 63mA for 230Volt, 125mA for 115Volt
Conforming to IEC127-2
FUSE TYPE 20mm x 5mm, Class 3 Slo-Blo, 250Volt working
CASE SIZE 482mm (w) x 44mm (h) x 200mm (d)
WEIGHT (incl packaging) 3 Kgs