DRAWMER DS404 OPERATORS MANUAL

CONTENTS:

SAFETY CONSIDERATIONS
INTRODUCTION
INSTALLATION
CONTROL DESCRIPTION
OPERATION
TECHNICAL SPECIFICATIONS

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 80mA WHERE THE MAINS INPUT VOLTAGE SWITCH IS SET TO 230 VOLTS AC. AND 160mA WHERE THE MAINS INPUT VOLTAGE IS 115 VOLTS AC. ALL FUSES MUST COMPLY WITH BS EN 60127-2:1991, SHEET III. 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.

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INTRODUCTION
The DS404 is a highly flexible but compact quad gate suitable for a wide range of professional applications including studio, live sound and audio installations. The input and output connections are electronically balanced on XLR connectors and low-distortion VCAs are used to maintain the highest possible signal quality. Although optimised for +4dBu operation, the DS404 will work equally well with systems operating at the -10dBu standard.

Designed to offer the greatest operational flexibility while remaining very easy to set up and use, the DS404 has two distinct modes of operation, Hard and Soft, and includes the same powerful side-chain filter system as pioneered in the Drawmer DS201. Each channel also has its own external key input.

In the Hard mode, the DS404 functions as a conventional gate with a very fast, preset attack time (under 10Ás) and a user adjustable release time. This mode is generally used for processing drums or other percussive sounds. To prevent the 'chatter' that afflicts some gates, a hold time is built in which varies depending on the setting of the Release control while the release curve itself has been modified to produce a subjectively natural decay response.

In Soft mode, the DS404 functions as a Programme Adaptive expander using the technology developed for the Drawmer DL241. This 'Programme Adaptive' expander circuit varies its ratio depending on the dynamics of the input signal, and in this mode, the attack time continuously adapts itself to suit the programme material being processed while the release time remains under control of the user. Because of the progressive nature of this expander, setting up is far less critical than for most other gates or expanders making 'Soft' gating ideal for general purpose cleaning up or for processing material with constantly changing attack dynamics. In either mode, the attenuation range is switchable to either -90dB or -20dB.

All four channels may be operated independently or linked for multi-channel operation. When used independently, any channel may be set to operate in either mode and with either range setting. When two or more adjacent channels are linked, the left hand channel becomes the master and the linked channels respond only to programme material arriving at the master input.

Each channel has a pair of key-filter controls enabling the gate/expander action to be made very selective. Essentially, the gate will respond to frequencies falling between the setting of the Low filter control and the High filter control enabling the user to choose a setting that will reject sounds that may otherwise present a risk of false triggering. To make the setting of these filters almost entirely instinctive, a key listen facility is provided which allows the filtered signal to be monitored at the output during setting up. These filters may also be used as processors in their own right and applications will be discussed at the end of this manual.

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INSTALLATION
The DS404 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 radiate significant amounts of heat. Always connect the mains earth to the unit. Use fibre or plastic washers to prevent the front panel becoming marked by the mounting bolts.

AUDIO CONNECTIONS
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 unbalanced operation, connect pin 3 to ground for both inputs and outputs, (best achieved inside the actual XLR connector). The key inputs are unbalanced ║" jack sockets.

If earth loop problems are encountered, disconnecting the mains earth is not recommended, but instead, try disconnecting some or all of the signal screens on the cables connecting the DS404 to the patchbay. If such measures are necessary, balanced operation is advised.

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 unit should always be connected to the mains supply earth using this cable

If for some reason the unit is to be used with a mains input voltage which is different to that as supplied, this procedure must be carried out.

  1. Disconnect the unit from the mains.
  2. Using a number 1 size pozidrive screwdriver, remove the two self-tapping screws holding the voltage selection switch cover plate on the rear panel.
  3. Remove the cover plate and slide the switch fully to its opposite end.
  4. Rotate the cover plate one half turn, (180 ) and refit the two screws.
  5. Replace with a correctly rated fuse for the selected operation voltage.
  6. Re-connect to mains power source.

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CONTROL DESCRIPTION
All four channels of the DS404 are identical and may be used completely independently or linked for multi-channel operation. In the linked mode, only the left most channel's controls are functional and serve as master controls, though the channel bypass switches remain independent. When linked, the control signal is derived only from the programme material present at the input of the master channel.

Threshold Sets the level below which gating starts to take place and may be set in the range -70dB to +20dB.

Display When the gate is closed, the red LED above the Threshold control is illuminated; when the gate is open the green and amber LEDs come on and the red one goes off. When the input signal falls below the threshold, the green LED will extinguish and the amber LED will fade over the duration of the release time. This is the same 'traffic light' system used on the Drawmer DS201.

Note: In soft mode, because the expansion ratio varies with signal level, it is possible to arrive at a situation where the red LED may be illuminated when little or no perceived gain reduction is taking place. This means that the expansion Threshold may need to be set a little higher than in the Hard mode and final setting is best done by ear. The adaptive expansion system used in the DS404 means, however, that setting up is not over-critical in Soft mode.

Release The release time may be set from 10mS to 5S and the control operates in a similar manner whether in Soft or Hard mode. A hold time is built into the system which varies with the release time setting. This is to prevent chatter when processing material with inconsistent decay characteristics and is quite invisible to the user. As a general rule, the release time should be set as fast as possible while ensuring that slowly decaying sounds, or sounds which include a lot of reverberation are not significantly shortened.

Range Determines how much gain reduction is applied when the gate is fully closed. The -90dB setting effectively silences the channel completely when the gate is closed while the -20dB setting will still allow an attenuated version of the channel signal to pass through.

Key Listen / Gate / Bypass When this switch is set to Key listen, the effect of the key filters on the programme material is heard at the output. In normal operation, the Gate position is selected; the filters only affect the way the DS404 responds to the incoming programme material - they do not have any direct effect on the output signal. However, these filters can be useful in certain applications in which case the switch may be left in the Key Listen position during operation. This will cause the audio signal to be routed through the filters but not through the gate. The Bypass position routes the input signal to the output with no processing.

L.F. The L.F. or Low Frequency filter is variable from 25Hz to 10kHz and works by severely attenuating frequencies below the cut-off frequency selected.

H.F. Variable from 200Hz to 35kHz, this filter attenuates frequencies above the selected cut-off value. In other words, when both filters are set, it is the range between the two settings that is allowed to pass.

Note: Any side-chain filtering which implements high frequency attenuation will also cause a slight delay in the time the gate takes to trigger. Under most circumstances this will be quite imperceptible, but when transient sounds are being processed with the H.F. control set to a very low value, some degradation of the attack transient may become apparent. For this reason, always set the H.F. control to the highest possible value practicable when processing percussive sounds.

Key/Int In the Int position, this switch causes the gate to respond to the dynamics of the signal present at the main signal input socket. In the Key position, an external audio source may be used to control the gate action making it possible to gate one sound according to the signal dynamics of another, independent signal.

Hard/Soft This button selects between the Hard and Soft modes of operation. In the Hard mode, the DS404 behaves as a fast, conventional gate while in Soft mode, it performs as a programme adaptive expander. Hard mode is signified by a red status LED while the Soft mode is identified by a yellow LED. If two or more channels are linked, the mode is determined by the master (left most) channel and the Hard/Soft LEDs on the slave channel(s) will extinguish.

Slave Link The Link buttons are located between channels, and when depressed, cause the channel on the right to be controlled by the left hand channel. Two, three or four channels may be linked, (or two pairs), the left most channel always being the master. In linked mode, the red status LED beneath the Slave Link switch will be illuminated, and both the yellow and red HARD/SOFT LEDs of the slave channel will be extinguished. This assists to show that the only controls of the slave channel that still function are the Key Listen / Gate / Bypass switch and the Range switch.

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OPERATION
The unit should be connected in-line with the signal to be processed via suitable insert points. Ensure, where possible, that the insert send and return level on your console approximately matches the operating level of the DS404.

For mono use, each channel may be considered as being completely independent and set up accordingly. For use with stereo or multi-channel signals, two or more channels may be linked; all setting up is then done using the left hand channel's controls in any linked group.

For percussive material such as drums, fast synthesised sounds or percussive bass guitar, the Hard mode of operation will give the fastest response. However, with material having a slower attack, the Hard setting may produce transient clicks at the beginning of sounds in which case the Soft setting may produce better results.

Initially, the Low filter should be set fully anti-clockwise while the High filter should be set fully clockwise. This will allow the full audio spectrum of the input programme to be monitored by the side-chain control circuitry. Set the Range control to -90dB and the output selector switch to Normal.

With the release control set at its mid-way position, Range set to -90dB and with suitable programme material fed into the DS404, increase the Threshold level from its anti-clockwise position until the gate starts to operate. This will be indicated by the activity of the traffic light LEDs and you should also hear the effect on the outputs signal in that pauses in the programme will now be silent. If the threshold setting is too high, the gate will start to cut out wanted pieces of programme so you should adjust it to as low a setting as possible consistent with the effective removal of low level noise. If the ends of sounds are obviously being truncated, then a longer release time may help. On the other hand, if unwanted noise is audible after the wanted sound has ended, a shorter release time may well be more appropriate.

There are circumstances when the programme material is corrupted not only by unwanted random noise, but by some other sound. For example, in a multi-miked drum kit setup, some hi-hat will inevitably leak into the snare mic, some snare drum into the kick drum mic and so on. Equally, when recording on location, you may experience problems due to wind or traffic noise or close-by conversation. If the unwanted noise is different in pitch to the wanted sound, it is often possible, by using the Key Listen facility, to use the filters to 'tune' into the wanted sound while excluding as much of the unwanted sound as possible. Used carefully, these filters can significantly increase the gate's immunity to false triggering.

LINKED OPERATION
It is important to note that when two or more channels are linked, the control signal is derived entirely from the left-hand channel in the group and not from a mix of the individual channels. This means that stereo signals where one channel differs significantly from another may fare better if the channels are not linked.

On the other hand, this mode of linking is very powerful in synchronising the start and finish of sounds, a typical application being to tighten up backing vocals. If one singer tends to finish notes on time while the others hang on too long, the correct version can be used as the master to ensure that all the others finish at the same time. Similarly, one sound can be used to gate another without having to resort to patching in an external key signal. An example might be to gate a low frequency tone from a bass drum signal and then add this gated tone to the drum sound to add depth.

DIFFICULT MATERIAL
As with any other gate, noise can only be removed during pauses in the wanted material. If the noise contamination is serious enough to be evident even during moderately loud programme material, then simple gating will do little to help. Indeed, the very fact that the gate produces near-perfect silence during pauses can make the noise content of the programme material seem even worse. In marginal cases, setting the range control to -20dB rather than -90dB will adequately reduce the noise during pauses but not sufficiently to cause an unacceptably dramatic change in noise level as the gate opens and closes.

More sophisticated processors such as the Drawmer DF320 are better able to cope with excessive noise as they adaptively filter the programme so as to mask the noise during low level passages or where there is little high frequency content present to mask it. However, the key filters in the DS404 may also be used to good effect, particularly in situations where the wanted signal does not occupy the full audio spectrum.

Taking the example of the electric guitar, this produces little below 100Hz or above 3kHz so setting one channel of the DS404 to Key Listen mode will enable you to use the filters to exclude much of the amplifier hum at the low end and hiss at the top end while having little effect on the sound of the guitar. Surprisingly, the same is true of the acoustic guitar; (even a bright-sounding steel-strung model), and the filters can be used to reduce the effect of string squeak or the player's breathing.

Other applications of the filter section include shaping DI'd electric guitar sounds to remove unpleasant overtones and to simultaneously clean and warm up digital synthesizer sounds. While we should always endeavour to get the highest quality of programme material at source, every engineer is occasionally confronted with inferior material from sources beyond his control. Conventional equalisers seldom have a sharp enough response do duplicate the function of the Key filters which invariably results in the wanted material being filtered as well as the unwanted noise.

Once a signal has been filtered in this way, it may also be processed by another channel of the DS404 to apply conventional gating.

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DS404 TECHNICAL SPECIFICATIONS
(All measurements reference +4dBu operating level)

INPUT IMPEDANCE 20K Ohms (Balanced)
KEY INPUT IMPEDANCE 20K Ohms(Unbalanced)
MAXIMUM INPUT LEVEL +21dBu
MAXIMUM KEY INPUT LEVEL +21dBu
OUTPUT IMPEDANCE 50 Ohms (Balanced)
MAXIMUM OUTPUT LEVEL +21dBu
BANDWIDTH <10Hz to 22KHz -1dB
FLOOR LEVEL -90dB, (or -20dB)

ATTACK TIME      Minimum      Maximum
Hard                    < 10 ÁS               -
Soft                      100 mS          1 mS

RELEASE TIME    Minimum      Maximum
Hard                     10 mS           > 5 Sec
Soft                      100 mS            5 Sec

NOISE     Wideband     22Hz - 22KHz     CCIR ARM     IEC A      Q-Pk CCIR
AV             -91dB              -97dB                -97dB       -100dB         -86dB
RMS          -89dB              -96dB                    -             -99dB             -

DISTORTION      100Hz      1KHz        10KHz
Gate Open with
+4dBu input        < 0.04%   < 0.04%    < 0.04%

POWER REQUIREMENTS 115Volt or 230Volt at 50-60Hz, 15 Watts
FUSE RATING 80mA for 230Volt, 160mA for 115Volt
CONFORMING TO BS EN 60127-2:1991 SHEETIII
FUSE TYPE 20mm x 5mm, Class 3 Slo-Blo, 250Volt working
CASE SIZE 482mm (w) x 44mm (h) x 175mm (d)
WEIGHT (incl packaging) 3.7 Kgs