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Ibanez DM2000

Digital Delay

Article from Electronics & Music Maker, January 1984

A new delay unit.



The DM2000 Digital Delay is not simply an update of the DM1000. Many improvements have been made on general operation and the inclusion of a 12 bit microprocessor has allowed a 10Hz to 16kHz bandwidth with delay characteristics inconceivable with the 8 bit processor previously used.

The DM2000, in common with other equipment in the range, is designed to be rack-mounted and compact, measuring just 44mm (1U) high. The outer metal casework has a hardwearing grey and bronze metallic finish.

Controls



An LED configuration on the left hand side of the front panel displays delay time from 0 to 1023ms, and two spot LED's flash on and off in sync with the duty cycle of the internal modulator. A headroom indicator, situated above the delay time readout, displays the input level of the delay signal (including signal through the feedback circuit) from -20dB to +6dB.

Two dual action switches reduce or increase delay time. As a matter of interest, it takes approximately 7½ seconds to change delay time from 0 to 1023ms, and in general the layout of the other front panel controls make for a swift and accurate effects changes. Four switches with LED inserts, are used to turn on the internal modulation, reverse feedback phase, switch delay mode to hold (for infinite repeat) and finally to bypass the lot leaving dry (unmodified) signal only. The bandwidth of the internal modulator and its duty cycle can be altered by two potentiometers, and feedback is continuously variable between a single repeat to run away oscillation. Dry and Delay outputs are controlled by two further pots on the left-hand side of the front panel.

Modulation, Hold and Bypass can also be controlled by foot-switches to the back panel, particularly handy in live performance, and pseudo stereo output is available under the guise of mix (dry and delayed signals) and inverse/mix (dry and delayed signal in inverted phase). A dry only signal out is also included in case you want to check that you are still playing and that the instrument isn't in complete control. An interesting feature is the external feedback loop. The send jack from the unit (input to external loop) comes after the first regeneration of the delay circuit and returns via the receive jack to the pre-mix stage. This offers as many possibilities as you have cyclic treatments but more about this later. Lastly, (or should I say firstly), the input is via a single high impedence jack which is switchable between -20dBm for line (PA and recording) and +4dBm for use with instruments.

Construction



The internal design matches the neat and efficient layout of the external. A sturdy steel framework holds all components rigidly in place and allows easy access to both sides of the two main PCBs once the two piece metal outer shell is removed.

In all there are 45 separate ICs in the main delay circuit board including an AM 2504 which performs the ADC/DAC work, and a D8048 12 bit microprocessor which duly carries out the three x's with the aide of 12 1K RAM chips. The unit is powered by a somewhat massive JKO8h transformer and tends to get quite warm after a period of useage. However adequate ventilation is provided, and a plastic screen which is there basically to protect internal wires crossing over the steel frame also gives some protection to the delicate ICs nearby. This might however be a consideration if this unit was sandwiched between two similar pieces of equipment in the rack.

The Modulation is derived from an internal LFO in the 8048 which should make for accurate sweeping of the delay time while flanging, chorusing and doubling.

After preamp stage the signal is pre-emphasised, low pass, filtered and compressed to prevent aliasing and quantisation noise at ADC. When the signal has been converted back in analogue form, it is expanded, put through a second LPF and de-emphasised, before being sent to output amps or feedback loop. This companding process combined with the added resolution of a 12 bit CPU offers a very good S/N ratio which is rated is rated as -95dBm by the manufacturer.



Effects



Various effects are available with equipment of this type and six sample settings of the popular ones are set out in a chart, thoughtfully stuck to the top of the rack mountable unit.

Flanging is produced by a series of notch pass harmonically related filters. This is induced in the DM2000 by sweeping the delay time by a ratio of up to 4:1 with the LFO (M.G), creating the phase distortion necessary to diminish cancellation.

You would expect that the LFO in this system would be of high quality and capable of giving full bandwidth sweep. The wave does give a very good symmetrical output and adopts delay characteristics very precisely. Unfortunately the excursion of the wave does not seem to be great enough to create an efficient flanging ratio (enough teeth in the comb) at high delay rate. Recommended delay is between 2ms-8ms which should give a bottom notch of about 62Hz but instead the effect is weak and barely noticeable even when presented with a fairly bright signal straight from a Quad 303 amp (which was the only time I lit the +6dB headroom indicator, with normal studio use it's difficult to present enough power to reach 0dB).

Chorus: This produced a better effect than the flanging, with higher delay time and no feedback. The sound had a definite fullness of tone but was still basically too weak in harmonics.

Doubling or Automatic Double Tracking is selected at 30-80ms delay, lower rate of modulation than chorusing, with a small amount of feedback. It creates an interesting, rich sound but despite its name it is not quite perceivable as a distinct echo: Once again the modulation let the DM2000 down, but things were improving.

Hard Reverb: take out the modulator, add extra feedback and the DM2000 starts to come alive. Although it lacks some of the presence of a good spring operated system, much greater control is available if sudden changes of reverb type, related to tempo or mood, are desired. With careful adjustments of feedback gain and dry/delay mix interesting subtle effects are available.

Slap Back: when delay is increased to 100-300ms a 'slap back' or 'bathroom' effect is produced. This is very effective at long delay rates but tends to be slightly abrupt at short regeneration cycles. However with careful adjustments of feedback rate clear and natural sounding effects are available.

Long Echo: the DM2000 offers delay times of up to 1023ms and regeneration can be set precisely. It is now that 16kHz bandwidth regeneration is particularly advantageous as regeneration does not detract from tone quality, and fascinating ostinati are available through switching feedback mode to hold.

Comments



Generally I found the DM2000 easy to use as it gave a great deal of flexibility over its various functions. Probably about the smallest, yet most annoying problem I found with the equipment was clicks made by the operation of the six switches on the front panel. Noise of the two dual action switches used to alter delay time unfortunately cut back its ease of use decisively. Feedback has to be reduced virtually to minimum when changing delay time or else audible clicks build up in the feedback in the same way that any other signal does. This can completely destroy continuity changing between, for example, echo and flanging.

The four other switches can also effect audio signal to a lesser degree if simple sounds such as sine-waves are input. The by-product of being able to produce a delicate raindrop effect with these clicks is of small consequence when overall performance is otherwise impaired.

Sound breakup tends to occur after about 30 seconds of reverb when feedback is set to maximum, and just becomes noticeable in the last few regenerations at lower levels as clipped attack.

The hold function allows easy access to infinite repeat with excellent reproduction of sound quality. The delay time needs to be set at 1023ms to effectively use hold mode as it automatically assumes 1023ms sequence time when switched in. Creating and adding to the sequence is straightforward; simply by switching in and out as each voice is added very complex ostinati can be produced (I had over 20 different timbres all reproduced with extremely clear accuracy).

Once you have your sequence it can be treated to pitch-shift using the modulator. However, as the shape of the LFO wave at this delay rate is very distorted there can be little practical use in this. Even so, very interesting effects, particularly when using speech from a microphone input, can be created. The maximum duty cycle of the LFO last about 23 seconds being 11½ seconds in each positive and negative phase.

The external loop adds extra creativity to the instrument. For example, sending the signal to a 2x frequency divider, inverting the output and high-pass filtering the result, gives a strange broadening effect at high delay rate, and interesting interaction of signal tones if delay is slow. Using it as one input of a ring modulator filtering the result and losing dry output can give very thick textures, and if you have a synth with ESP (external signal processor), the sent signal can be used to trigger other equipment or for envelope following. These are a few uses which I found interesting, but there are many more, and the loop is definitely a good feature for studio use.

Conclusion



I can't help feeling that the design of the DM2000 has been hampered slightly by trying to appeal to a wide range of users. Problems I experienced while flanging etc. using outputs directly from synths (with input selected to -20dBm) are reduced considerably when the unit is fed with a power amp and switched to +4dBm. I found it impossible to attain the required reading on the headroom indicator with either synth or guitar, and yet when powered by a Quad 303, headroom could be made to peak at the suggested +6dB, and effects were better, but still not good.

For live performance foot switches can control on/off function of modulator hold and bypass (good quality switches are a must, especially on hold, to prevent noise). However, the external loop facility is badly thought out for live use, when a plug is presented to send output at the back, the front panel control is switched out of the circuit (except that if turned fully anticlockwise, feed-back is still reduced to a single repeat). This means that in live performance, if you want to change from external to internal feedback loop, the jack plug needs to be removed from the back panel. This should be switchable from the front to realise the full potential versatility in live performance.

The positioning of the -20dBm/+4dBm switch at the back next to the input jack could be better, but you can't have everything at the front and you are very unlikely to need to use it live.

The DM2000 is designed to be a digital delay unit, and as such, it does an excellent job with a S/N ratio that allows for a great diversity of signals to be treated with a crystal clear reproduction of timbre, I would definitely like to see the delay time limits extended at both ends but even as it stands, this equipment offers extremely good value for use either live or in a studio environment.

RRP of the DM2000 is £395 (inc VAT).

Further information from Summerfields, (Contact Details).


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Browse category: Studio FX > Ibanez



Previous Article in this issue

Fender 'Hot Duo' Tour

Next article in this issue

Modular Synthesis


Publisher: Electronics & Music Maker - Music Maker Publications (UK), Future Publishing.

The current copyright owner/s of this content may differ from the originally published copyright notice.
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Electronics & Music Maker - Jan 1984

Donated & scanned by: Stewart Lawler

Gear in this article:

Studio FX > Ibanez > DM2000 Delay


Gear Tags:

Digital FX
Delay

Review by Glenn L. Hughes

Previous article in this issue:

> Fender 'Hot Duo' Tour

Next article in this issue:

> Modular Synthesis


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