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Digidesign Turbosynth

Synthesis Software

Article from Music Technology, September 1988

CAD meets synthesis inside the Apple Mac. Robert Rich fires up a program that allows you to design your sounds on computer before transferring them to your sampler.

Does this new program for the Macintosh demonstrate that "serious" software synthesis is a concept whose time has finally come?

Main Patch Screen

I MUST CONFESS, I don't really like the sound of samplers. Images of chipmunks and Darth Vader have poisoned my ears; orchestra hits and shakuhachis; endless stuttuttuttering political snippets... Surely there's more to sampling than this.

Apparently, Digidesign's design team agree because they've devised a new program called Turbosynth. Turbosynth lets you patch together various digital signal processing modules - all in software - to create your own sample generating algorithms. These patches can incorporate digital samples, additive, subtractive, FM and AM synthesis, waveform crossfading, filters, and several different kinds of modifiers. Turbosynth then lets you export the results to your sampler.


TURBOSYNTH RUNS ON a Mac Plus, SE or Mac II, with a minimum of 1 Meg of memory. You'll need at least 2 Meg to do anything really ambitious, though. Even some of the example files were too big for my 1 Meg SE.

I tested version 1.0 of Turbosynth with no problems on Apple's System 4.2 (Turbosynth comes with 5.0). However, Digidesign say that Turbosynth has some problems running on Apple's new System 6.0, so Digidesign intend to provide upgraded versions of Turbosynth for registered users who have the new system.

Turbosynth will work with many different samplers - currently the Akai S900, S700, X7000; Ensoniq EPS and Mirage; Roland S50, S550, S10, S220, MKS100; E-mu Emax and EII; Korg DSM1 and DSS1; Casio FZ1; and Yamaha TX16W. It also speaks the MMA Sample Dump Standard, adding the Sequential Prophet 2000/2002, Dynacord ADDone and Simmons SDX to this list. The program defaults to the most commonly used sample rate for each sampler, but you can change it if desired. Unfortunately, Turbosynth cannot send stereo samples. Shame.


FOR ALL ITS complexity, Turbosynth is mercifully easy to understand. It works like a modular synthesiser, with little boxes representing various components in the signal path. The screen offers a large palette of module icons. You simply click on the icon of the module you want to use, then click on the screen where you want that module to appear. A patchcord icon lets you connect these modules. You can change this "wiring" or move modules around at any time. At the end of the chain there is always an Output Jack icon, which represents the output sample.

Before you can hear the sample from the Macintosh speaker or send it to your sampler, you must tell the Mac to calculate the results of the patch by clicking on a Speaker icon. The Mac takes a few seconds to calculate any new changes in the patch. Another click on the speaker icon will let you hear the sound from the Mac. Turbosynth earns high marks for its speed. It seems that it can calculate a complex additive algorithm at least as fast as Digidesign's own Softsynth (probably faster).

The program works with three kinds of files. Document files store the Turbosynth "patches," including module parameters, interconnections, and sample data. These document files are very short if they contain no samples. Turbosynth can also read and save sound files in the Sound Designer format, and waveform files containing sound data representing regular repeating waveforms. You can create waveform files from samples within Turbosynth by opening a Sound file, creating a small loop, then saving that loop as a waveform (or you can draw waveforms by hand.) Turbosynth can then use these sampled waveforms in its oscillators.


THERE ARE 13 DSP modules, counting the Output Jack (which automatically appears at the bottom of each new patch screen). The other 12 icons sit in a palette at the left of the screen.

The program lets you cut, copy, paste, delete, or move modules around, just like MacDraw or any other graphics program. Double clicking on one of the modules opens up a window showing the parameters for that module, with an appropriate assortment of tools. These windows vary from module to module. The simplest windows show sliders, allowing you to adjust certain basic parameters. Other windows provide flexible envelopes (similar to those found in Softsynth), while modules containing wavesamples provide wave editing environments similar to Sound Designer.

Every module window contains a speaker icon, which means you can hear a signal's development anywhere along its path. Also common to every module is an information box, accessible by clicking on an "i" icon. All module info boxes let you name the module, and also let you change the sample length (in number of sample points) and sample rate (in Hz). A similar info box in the main patch window lets you set default values for the length and rate, but you can specify different values for each box if desired. Also in each module info box, a "normalise" button adjusts the signal level so that the highest peak will be as loud as possible without clipping, thus improving the signal-to-noise ratio. Two other buttons in the info box select the module's playback rate from the Mac's speaker. Choosing the button for the Mac's rate will let you hear the module's output at highest fidelity on the Mac, but will change the pitch if the module's sampling rate is set to something other than the Mac's 22kHz. Let's take a look at the modules:

Oscillator Module

Turbosynth distinguishes between Sample modules and Oscillator modules - Sample modules play sample files, Oscillators work only with repeating waveforms. But the oscillators in Turbosynth can do a lot more than just generate static waveforms.

The Oscillator window consists of a timeline representing the length of a sample. You build sounds by pasting waveforms onto this timeline. The oscillator automatically crossfades between these waveforms, allowing timbral changes to sound quite natural. You can select one of 15 preset waveforms by clicking on its icon, then clicking on the point in the timeline you want it to play. Presets include sine, triangle, sawtooth and square waves, some harmonic multiples of the above, and a few more complex waveforms. If you want to use something more unusual, you can open previously stored waveform files and select from those. Each waveform icon shows a little picture of the wave it represents, making everything blissfully easy to figure out.

To edit a waveform, just double-click on its icon in the timeline. A window opens showing a single cycle of the selected waveform and a number of editing tools. The same 15 preset waves appear here as before, along with the icon for opening waveform files. A pencil icon lets you draw waveforms by hand, and ten waveform modifying tools let you alter them globally. These icons adjust the amplitude of different parts of the wave (or induce clipping if desired), skew the wave left or right, add randomness (noise), or smooth the wave (reducing overtones). Considering how hard it is to hand-draw a waveform, the smoothing tool is a particularly wonderful facility.

Turbosynth lets you name custom waveforms and save them as waveform files by selecting Save Waveform on the Mac's file menu. Any waveforms you create can thus be used in any Turbosynth patch.

Sample Module

Data from any of the supported samplers can be imported into a Sample module, as well as any Sound Designer file. Turbosynth will also create samples from any other module or group of interconnected modules in a patch. You can save any sample as a Sound Designer file, which means that you can further tweak these sounds in Sound Designer or Blank Software's Alchemy.

The Sample Module window shows a waveform representation of the sample, with a tool palette including an eraser and Loop icons. The eraser can only erase loop points. There is no pencil tool, nor can you create crossfade loops. The Loop icons select the start and end points of a loop, which you can then fine-tune in the Loop window. The Loop Window shows the adjacent start and end points of a loop, with the end portion on the left and the start portion on the right. To move the loop points to a particular point in the wave, just click on the desired point and the loop point will appear there. Scroll bars let you nudge the loop points to remove glitches. Vertical and horizontal zoom buttons let you scale the amplitude and frequency resolution of the loop editing display, but do not affect the sound.

Sample Screen

"Crossfading: The oscillator automatically crossfades between waveforms, allowing timbral changes to sound very natural."

Once you've found a loop that sounds good, you can save it as a waveform file for future use in an oscillator, or you can fill out the remainder of the Sample module's buffer with copies of the loop. Turbosynth will not otherwise use the loop. In other words, a Sample module represents a one-shot sample - the loop within a Sample module is not the same as the loop used to sustain a note in your sampler. This latter loop is created in the Output Jack module. This difference allows many Sample modules to play at once, each with different loop points.

As you may have noticed, the Sample module provides only the basics for editing. I would complain about its inadequacies if I felt they really mattered, but these limitations get lost in the overall flexibility of Turbosynth.

Amplifier and Filter Envelope Modules

These modules do exactly what you would expect, acting like analogue VCAs and VCFs, with envelopes built into each module. Unlike their analogue forefathers, these envelopes have unlimited segments. Both modules provide several preset envelopes, which you can bend around with the mouse by clicking on any point and moving it. Four envelope modifier buttons create global changes by altering sustain levels or skewing the envelope parameters in time. Unfortunately, I could find no way to copy envelopes between the two kinds of modules.

The Filter module provides only low-pass filtering, which seems unnecessarily limiting. I would have loved to see band-pass filtering and resonance. The filter offers a cut-off slope of 6db/octave, which can be increased by daisy-chaining several copies of the same module. The cutoff frequency only goes down to about 500Hz, but this is generally sufficient. When chained together these filters sound quite good - even "analogue".

Spectral Inverter & Waveshaper

The effects of these two modules are a bit harder to describe. The Spectral Inverter module inverts the harmonics of a waveform around the halfway point of its bandwidth. If the sample rate is 20kHz, the bandwidth will be roughly 10kHz, and the halfway point is 5kHz: the spectral inverter would then move an overtone at 6kHz to 4kHz, or an overtone at 1kHz to 9kHz. In practical terms, this will make most waveforms sound hollow or metallic. It generally works best for very bright waveforms, where the results an be quite pleasant and unusual.

The Spectral Inverter window provides an envelope just like the amplitude and filter envelopes, only this envelope controls the mix between normal and inverted signals. Nice touch.

Waveshaping (a technique used a good deal in Buchla's digital synthesisers) is one of the more interesting modules in Turbosynth. This module provides a transfer function which maps the amplitude of incoming sample points onto different amplitudes according to a graph which you can edit. This graph shows the input and output levels on horizontal and vertical axes, with its range covering the dynamic range of the sample. For example, if the graph shows a straight line from lower left to upper right corners, it will leave the signal unaltered because every input level will map to its identical output level. If a line goes from upper left to lower right, it will invert the signal by 180 degrees. If the transfer function is bumpy, then it will add lots of overtones to the signal. The results become more difficult to predict on more complex curves. The Editing window provides several shaping tools, preset curves and a pencil to draw your own functions.

Modulator, Delay...

The Modulator module lets you create more than just the FM sounds made famous by Yamaha. Any two signal inputs can modulate each other, including samples from the outputs of any Turbosynth module. Two sliders are the only controls on this module: one for modulation amount, the other for mixing modulated with dry signals. One input can modulate either the frequency (FM) or the amplitude (AM) of the other. AM synthesis sounds different from FM, and it is a refreshing addition to Turbosynth. The Modulator module also allows pitch modulation, which is essentially FM optimised for chorusing and vibrato effects.

The Delay module simply creates echoes out of the signal. Controls include coarse and fine delay time, feedback, polarity inversion and wet/dry mix. The one thing missing is a frequency sweep for flanging effects.

Similar to the delay module, the Resonator module works with short delay times to create ringing delays. Instead of delay time, its slider controls show resonant frequency (again, no sweeps).

The Pitch Shifter module transposes sounds by using linear interpolation (thereby extending or shrinking their duration proportional to the amount of shifting). It can range over +/-2 octaves, with slider controls for pitch and wet/dry mix.

The Stretcher module increases the length of a signal by scanning through it with a loop of definable length, copying the segments within that loop as it goes along. This only sounds natural with harmonic waveforms where you know the fundamental frequency. Otherwise it induces some interesting distortions. Its sliders control coarse and fine loop frequency, predelay before stretching occurs, and the number of times each segment gets duplicated.

The Mixer module contains as many sliders as there are modules entering the mixer. Since most of the modules described above can only process one input, the mixer serves to merge many sources into single module inputs.

Finally, the Output module has a window much like the Sample module, only here the loop point really is the sample loop. You can create both sustain and release loops, but the distinction only matters with the Prophet 2000.


DIGIDESIGN CLAIM THAT Turbosynth is a fairly open-ended program, and they hope to add further modules in the future. Indeed, I have a short wish list of features I would love to see like pitch envelopes, which would really help, although the Modulator module lets you work around this (draw your envelope as a waveform in an oscillator, set it to a very low frequency, then use it as an FM modulator). I would also love to see a module that "convolves" two samples like the Emax SE. The Filter module could be beefed up, and the Delay and Resonance modules could incorporate frequency sweeps. An envelope copying function would also prove helpful. Since one of the main philosophies of Turbosynth was having speedy processing modules, we'll have to see what Digidesign can add before compromising this.

As a final comment, I should mention that synthesis for a sampler is not the same as on a synthesiser. Any time-variant synth effects will suffer the same problems that plague acoustic samples. Envelopes will expand and contract across the keyboard. Chorusing will speed up as you move up the keyboard and will also make looping much harder. By creating certain effects within the sampler rather than in Turbosynth, you can avoid many of these problems. Nevertheless, Turbosynth does not overcome the inherent shortcomings of the sampling process.

I really like this program. I had so much fun working with it that I could scarcely tear myself away to write this review. Like any good tool, Turbosynth is easy to understand, yet it has enough depth for years of exploration. It can create a huge variety of sounds, from simple to complex, ugly to beautiful. If you have the equipment and you want new sounds, take a serious look at this program. It's not cheap, but it's worth it. I can't wait to start patching again...

Price £285 including VAT. Also available for the Atari ST at £235 including VAT

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The Power Of The Voice

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

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Music Technology - Sep 1988

Donated & scanned by: Mike Gorman

Review by Robert Rich

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> The Power Of The Voice

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