Delta Lab DL-5 Harmonicomputer
If you've always wanted to run the world whilst seeking the answer to the Ultimate Question, then a harmonizer is just the ticket, as it's particularly proficient at making mice of men (apologies to John Steinbeck). The same holds if you're into "foonting turlingdromes", and, as a friend behind the scenes at the Beeb put it, "space monsters would still be ring modulating each other if it wasn't for harmonizers". Eventide started the ball rolling with the first harmonizer in 1975; the Delta Lab DL-5 is one of the latest units to appear on the market, but, at £1,300, it's hardly cheap.
Until recently, harmonizers attracted a good helping of brickbats on account of their tendency to impose rather too much of their own personality on whatever was fed into them. This effect was given the picturesque description of 'glitching' and stems from the way in which the harmonizer customarily goes about its business. The basic principle is to read the input signal into memory and then clock it out at a different rate to get the transposed pitch. Unfortunately, during this read/write process, it's necessary to either cut out or add in cycles in order to create a continuous audio output. This well and truly mucks up the time base of the original signal, and one's left with the problem of how to fit the stretched waveform into the original space, or, in the expansion situation, what to do with the space left over after the waveform sample has been shrunk down. The obvious point of this bit of digital splicing is to smooth out the output signal so that it sounds as natural as possible. Not surprisingly, the further the harmony is removed from the original pitch, the more difficult it is to make a successful splice, and, as most harmonizers are far from 100% accurate in doing this, you end up with the aforementioned 'glitches', or, as somebody put it, "the notes get lumpy".
With the early Eventide harmonizer (now manufactured with all manner of deglitching circuits), an interval of a 4th or 5th was asking for trouble, and the only way in which you could use such digitally generated 'harmony' was to put it somewhere like 30 dB below the original signal level, i.e., using it for a touch of colouring. The DL-5 takes the eradication of the glitching problem a good deal further, but it's still there, albeit as a reasonably subtle amplitude modulation that increases in speed as you get to the maximum of an octave above or below the input signal. This means that it's pretty important to keep the higher harmonic intervals at a reasonable level in the mix, but, then, if you're playing a top A at 7,040 Hz, it's unlikely that you'd want a 14,000 Hz octave harmony at an equivalent dynamic level. The other thing to bear in mind is that, unlike simple 'harmonizers' like octave doublers/dividers, units like the DL-5 are quite happy with any waveform fed into them — and that includes any sort of complex polyphonic information — even a Beethoven piano concerto!
Sleek and colourful describe the DL-5's appearance, as the sea blue front panel is just 1¾" high in the standard 19" rackmounting format. Starting on the left side of the panel, there are two columns of LEDs labelled Peak and Slew Headroom. Moving stage centre from this visual feedback and an input level control, we come to the main crux of the matter, the 13 rocker switches for choosing one's harmonic message. By depressing each switch in the up direction, the harmony produced by the DL-5 increases in a chromatic scale fashion. Similarly, by depressing each switch in the down direction, the harmony descends into the depths of Vogonic despair. The pitch selection is voltage derived, with each ½ tone increasing/decreasing by 0.083V. Thus, +1V gives one octave lower, +2V no pitch shift, and +3V one octave higher. This arrangement makes external pitch control very straightforward and there's a jack on the back panel for this purpose. A fine tune control is also provided and this varies the overall tuning by approximately ± half a tone. The fixed keyboard control can also be disabled to provide the option of using the tuning control as a two-octave pitch sweep. Since the unit sensibly uses the 1V/octave standard, presumably any linear CV-producing keyboard could be plugged into the external pitch control input. To my ears, the more one progressed from the original pitch, the more a quick twiddle of the fine tuning was needed, but the tremolo effect caused by the small amount of glitching present may have contributed to any impression of slight pitch discrepancy.
Next to the tuning control, there's a white box containing the controls for the Time Base Processor. The first two knobs control an LFO, with variable width and speed, that modulates the pitch shift producing characteristic vibrato effects. In practice, the narrow width (small pitch shift), slow speed effects work best, and, with just a slight amount of pitch shift selected, produce a really rich chorusing. Demo cassette No. 7 includes an example of this — making stereo out of mono! The Feedback control allows the pitch-shifted signal to be written back into memory to be further shifted, and so on. Thus, a single note or chord can be encouraged to perform a short arpeggio, upwards or downwards, based on the chosen pitch shift. This can lead to amazing Doppler-like effects which really create an extraordinary sense of ambience. The effect can be further heightened by adding in more delay (with the Delta Lab DL-4 Delay Line, for instance) into the return of the regenerated signal. Curiously, with longer delays between successive pitch shifts, and even though it's the pitch rather than the amplitude that's changing (the latter being the situation with reverb), the ear is fooled into thinking it's hearing the effect of ambience.
Obviously, you could use the DL-5 to provide harmony and it's particularly effective at doing this with vocals. However, the situations in which you can use a 4th or 5th above or below the lead vocal throughout a track are pretty rare (a short-cut to parallel organum, perhaps?), and this is the point where an external keyboard control (or pedalboard, perhaps) would be pretty useful for selecting harmonies at will. Who cares about backing singers if you've got a harmonizer instead!
The technical specifications of the DL-5 are impressive (frequency response: 20Hz to 15kHz ± 3dB; dynamic range: 90dB) and the unit is superbly constructed. Delta Lab's delta modulation techniques enable them to get these sorts of figures and they're also able to chuck out those less than ideal antialiasing filters common to any PCM system. Delta modulation obviously works well, and, if as they say, it's cheaper and easier to implement than conventional digital encoding/decoding techniques, then it'll be interesting to see what other products switch over to their way of thinking.
One point that concerns me is the discrepancy between what Delta Lab claim for their unit ("innovative multiplexing techniques totally eliminate the typical splice-glitch... the result is a clean sounding harmonizing unit that is not plagued with unnecessary side effects") and what I actually heard from the unit. Glitches are present, and there is a 'halo' of noise around everything that comes out of it. To be fair, the unit I had for review from Scenic Sounds was their peripatetic demo sample and it may well have been subjected to brutal, glitch-inducing knocks. It's a tough life being a harmonizer!
The Delta Lab DL-5 is available from Scenic Sounds, (Contact Details).
Review by David Ellis