[music-dsp] Open Source DSP Analog Simulation Synth
theover at tiscali.nl
Wed May 13 14:28:47 EDT 2009
Eric Brombaugh-2 wrote:
> robert bristow-johnson wrote:
>>> The general idea is to marry a low to mid-range FPGA to a reasonably
>>> ......IDI monosynth which only uses less than 20% of the FPGA resources.
>> but what if you want dozens of voices simultaneously?
> The present design is just a step along the way. For polyphony I'll be
> extending the FPGA logic to handle many simultaneous voices - I'm
> estimating that I can get several hundred oscillators running at once.
>> i know of at least one company that had been exploring this for
>> multi-voice sample playback (the FPGA is doing all of the sinc-like
>> interpolation effort). then they're gonna couple the sample-playback
>> output into their existing chips for processing and effects which is
>> really dumb. they had (and it isn't me) one insightful engineer who
>> suggested also doing whatever necessary processing on individual voices
>> on the same FPGA, but they didn't listen to him either.
> Just using the FPGA for sinc interpolation seems short sighted, but I
> imagine they're thinking along the lines of "we've already got the
> hardware/software synthesis problem nailed with our existing solution".
> Not very forward-looking, but probably cheaper and quicker to market.
Open source is of course not the same dreamboat as commercial enterprise,
but fundamental issues are for instance: what will voices do like sampling
wise, delay-wise, accuracy-wise and how and how accurate and fast can they
be controlled. Analog synths of 5 decades ago can easily be better at many
of these issues than a nifty new fpga or dsp design when no care is taken.
Also, many sounds based on samples are based on assumptions about the
playboack equipment being used, and uses transforms which are seldom a
bijection (i.e. impossible to invert by external processing to the original,
An important issue IMO is bandwidth limited oscillators (after my above
synth design and prototype had received some attention but little feedback I
was glad to read the latest kurzweils had ' bandwidth limited generators'
even while of course I knew that is normal. A saw or triangle oscillator for
a ' normal ' synth design which is well frequency band limited as to prevent
aliasing, not even counting the spectrum of the multiplied ADSR or
(theoretically) unlimited FM (bessel) spectrum of a swept filter resonance,
can take more than a little work, and most commonly used interpolations are
really very far from the sonic quality I like to monitor, granted on a
extensive monitoring system, but many modern sounds sound alike and annoying
also on a good notebook amplification, for instance, and all that seems most
of the time to be taken for granted. That's among the reasons many not so
much adding designs of musical synthesizers remain decades and many quality
levels behind lets say a cheap enough second hand motif or so, with 64 or
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