STUDIO

BSS DPR -502A user report on a MIDI noise gate fromBSS. By Dave FoisterWith so much recent outboard gearfalling into the multi- effectscategory it is becoming somethingof a rarity to see a new productdevoted to one specific purpose. Those that chooseto follow this path generally have to havesomething slightly special about them in order tocompete and avoid inspiring a feeling of déjà vuin the potential user. This is particularly truewhen the designers decide to shun fashionablealphanumeric displays, incremental dials, nudgebuttons and all the other paraphernalia of digitalcontrol in favour of knobs and push switches. BSSAudio's DPR -502 gate opts for the traditionalapproach in both areas.In layout and operation the DPR -502 couldhardly be more familiar. In most respects it is aconventional 2- channel noise gate, providingfrequency -conscious gating, comprehensiveenvelope control, stereo linking, ducking, externalkeying, side chain access and the familiar 5 -pinDIN sockets, but has a few additions andvariations to set it apart from the crowd.The familiar bits all perform to a high standard.BSS's choice of a control panel featuring lots ofknobs is a deliberate one. They clearly feel (and Iam inclined to agree) that for all the cleverness ofdigital control systems, you can't beat theintuitive feel and speed of a good old -fashionedcontrol knob. So many devices, including gates,rely for their set -up on the interaction of severalparameters, and the laborious process of callingeach parameter to be edited in turn, can nevermatch the directness of adjusting a group of real,constantly- active knobs.The parameters, in this case, include the usualtime controls for attack, hold and release, plusthreshold and range, all of which provide a usefulcontrol range coupled with a sensibly- chosencontrol law making adjustment easy. Fastestattack time is 20 µs, which sounds less impressivethan some manufacturers' specs although BSSpoint out that it is a true attack time to fullyopen state, so comparison with othermanufacturers' figuresmay be misleading. Manymanufacturers calibrate time values in terms oftime per so many dB of gain change -like a slewrate -which isn't the same thing at all, but Iwonder how many users read specifications insufficient depth to notice this?Other familiar controls include bypass switches;on the 502 these are big, red and illuminated -you can't miss them. It seems strange to me,however, that they are so close to the mains on/offswitch, whose accidental operation could bedisastrous. I am always puzzled why equipmentlike this has to have a mains switch at all. Howmany engineers go round switching eachindividual piece of gear on at the start of asession? If some obscure regulations make themobligatory (and if this is the case why does somuch gear not have them ?) then they should atleast be tucked safely away from the device'smain controls.The first obvious deviation from the norm onthe 502 is the method of controlling the sidechain to achieve frequency- conscious gating. Mostgates use a pair of high- and low -pass filters toremove unwanted frequencies either side of awindow containing the wanted signal. This is finein most cases but still gives a critical set -up onmany signals. The 502 on the other hand uses aparametric equaliser -style bandpass filter, whosecentre frequency can be varied between 30 Hz and15 kHz and whose bandwidth is adjustable from10 octaves down to half an octave. Obviouslywhen this is set as wide as 10 octaves iteffectively isn't doing anything. For this reasonno in/out switch is provided -the filter is alwaysactive in the side chain which means its settingshould always be checked when resetting the gatefor a new use. I found this approach easier to use(particularly on difficult signals), than the morefamiliar one. It seems much simpler to home inon a particular useful frequency area than to findthe wanted bit by a process of elimination.A non -latching check switch is provided formonitoring the effect of the filter and, unusually,an internal user option allows this check signal tobe brought out separately from the main outputso that it can be monitored while the gate is`live'. Unsurprisingly this filter arrangementremoves so much from the input signal atextreme settings that it interacts with thethreshold control, requiring the use of a lowerthreshold as the bandwidth is reduced. However,this is usually the case with a frequency -consciousgate and presents no problems- indeed theintended result is usually a less critical thresholdsetting anyway.Setting the threshold and following the gateaction is greatly simplified on the DPR -502 by theimaginative and informative metering display. Oneach channel, a row of LEDs displays a `window'of levels either side of the selected threshold (redabove, green below). A bar of LEDs with vu -typeballistics shows the continuous signal level(relative to the threshold) while a peak LED holdsthe transients on the display for a short time. Inaddition, a red triangle points at the thresholdsetting and lights while the gate is open. All ofthis is considerably more useful than the usualthreshold light; it shows how far below thethreshold the unwanted signal is and exactly howfar above it the wanted peaks are, greatlysimplifying the set -up on most signals,particularly drums. It is also useful when settingup the MIDI response, but more of that anon.Envelope control is made more comprehensiveand potentially creative by the inclusion of a veryeffective Auto Attack mode, which claims tooptimise the attack time to react as fast aspossible without distortion, and what BSS call theAuto Dynamic Enhancement (ADE) facility. BSSclaim this is unique, although the DrawmerM500, for one, incorporates something verysimilar. In order to overcome the apparent loss oftransient punch which a deliberate gain overshootwhen the gate opens, so that initial peaks areenhanced before the gate -open gain reverts tounity. Thesize of this peak can be pre -set to either3 to 4 dB or 6 to 7 dB. The switch for selectingthis is located on the rear panel while the in/outswitch for the function is on the front. Thiscertainly works very well and, particularly at itsmore extreme setting, can be used as an effect inits own right, exaggerating bass drum click andsnare crack.The MIDI facilities take the now familiar MIDIgate functions (funny how recently they wereinnovative and exciting) and expand them a little.As one would expect, each channel sends a NoteOn command every time it opens and a Note Offwhen it closes. The velocity byte of the commandcan be either fixed at 64 or variable between 10and 127 according to the audio signal amplitude.The 502's metering comes.in particularly usefulfor setting up the dynamic tracking, since thevelocity value depends on the amount by whichthe signal exceeds the set threshold.The obvious use for this is to replace recorded orlive drums with samples or MIDI drum machinesounds, or to add further sounds triggered fromthe real drums. The ability to see clearly therelationship between audio level and MIDIvelocity makes it easier than ever to preserve thefeel of the original drummer in the context of thenew sounds. The only problem I encountered isperhaps inevitable iii this situation, and involvesthe conflicting time value requirements for actualaudio gating and MIDI triggering. A sensibly setgate on, eg a snare, will stay open long enough to108 Studio Sound, June 1989