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Digital Subtractive Synthesis

Posted: Fri Jul 20, 2012 6:32 am
by visceralvoids
I got a hold of the Roland D-50 Creative Manual from a link in the reviews on this site. I came across this term Digital Subtractive Synthesis and it's what Roland calls a subtractive synth engine, with PCM samples. My questions were: Is the D-50's synth engine complete enough for programming sounds? Is the D-50's sound character due to use of "rough" 8/12 bit samples + special DAC? What exactly is the method the D-50 uses for Digital Subtractive Synthesis.. been wondering this for a long time.

Re: Digital Subtractive Synthesis

Posted: Fri Jul 20, 2012 6:59 am
by mharris80
visceralvoids wrote:I
What exactly is Digital Subtractive Synthesis.. been wondering this for a long time.
Haven't really played a D-50, so I can't answer the first two. I'll take a stab at the last one, though. Basically, it's the same as analog subtractive synthesis. The only real difference is the method of tone generation. Either way, you've got a waveform, and you're using a filter to remove certain harmonics from it. And that's pretty much it. It's just a matter of whatever your ears happen to prefer.

Re: Digital Subtractive Synthesis

Posted: Fri Jul 20, 2012 1:24 pm
by Bitexion
Absolutely, the engine is good enough to program both your typical analogue sounds and more esoteric sounds.

The PCM samples aren't samples of complete instruments, just the attack section, like the bow hitting a violin, the "chiff" sound when you blow into a trumpet. So you can get more realistic sounds that way. Some times they're looping, sometimes they're just a short attack section, sometimes they're totally digitally made looping waveforms.
There's also a bunch of weird loops at the end of the wavetable that change playback rate according to pitch.
The "famous" clockworks sound from JM Jarre's Revolutions Overture for instance is one of those loops being triggered in two octaves, effectively halving the playback speed on the lower note, making it into a thumping rythmic loop.

Esentially the engine consists of 4 separate 1 oscillator polysynths (parts), each with its own digital lowpass/highpass filter, pitch, LFOs, envelopes, and two waveforms (a saw-ish one and square/PWM). The sawtooth isn't your usual "thin raspy" sawtooth, it sounds alot heavier and fuller due to it being shaped more like a shark fin than a pure sawtooth.
If you use a PCM sound you're swapping out the oscillator in the part with the sample.

You also have looping samples of lots of Hammond drawbar settings to combine into great hammond sounds, with PCM sampled clicks as you like. You also have some ringmod configurations that prewire two parts together in a ringmodulator that lets you do the usual ringmod sounds with Envelopes or LFOs.

So yeah, you can make massive detuned 4 oscillator saw sounds, or make it sound like a string orchestra too. It's a very flexible synth, and the interface is covered in shortcuts that give you easier access to the 4 parts parameters.
You have a X-Y joystick controller which acts as a realtime mixer between the 4 parts, sadly it can't be used for realtime parameter changes like filter cutoff, but you can use it for data entry while programming.

I have a D-50 and have programmed lots on it during the years.
It's not necessarily a "worse" type of synthesis than analog subtractive synthesis, it's the same concept. You start with some waveforms (sampled, real analog, virtual analog, doesn't matter), send them through a filter to "subtract" frequencies and harmonics, and modulate various parts with envelopes or LFOs.

Re: Digital Subtractive Synthesis

Posted: Sat Jul 21, 2012 3:15 am
by Music Maven
Bitexion wrote:It's not necessarily a "worse" type of synthesis than analog subtractive synthesis, it's the same concept. You start with some waveforms (sampled, real analog, virtual analog, doesn't matter), send them through a filter to "subtract" frequencies and harmonics, and modulate various parts with envelopes or LFOs.
Just to be clear (for the original poster's benefit,) it's not possible to route the D50's sampled waveforms through its filter. That's one of the D50's most significant limitations. Despite that, the D50 has a sound all its own. It's still a great synth.

Re: Digital Subtractive Synthesis

Posted: Sat Jul 21, 2012 11:53 am
by Bitexion
Yeah forgot to mention that. Once you select a PCM waveform the filter on that part is bypassed. Still have the filter on the other parts of course.

Re: Digital Subtractive Synthesis

Posted: Mon Jul 23, 2012 2:15 am
by piRoN
Yes, the D-series actually do the "filtering" by changing the harmonics at the waveform generation stage, so there's no real filter to send the PCM samples through.

I'd be interested to know exactly what algorithm they used for the oscs, it's a quirky way to emulate subtractive.