[sdiy] *EXT* Re: Becoming better at understanding difficult analog schematics

[rburnett at richieburnett.co.uk]

For Virtual Analogue I want to model the behaviour of a particular 
*circuit* digitally.  (Even if it doesn't really sound much like a real 
snare drum or cymbal!)  LTspice gives me a "first step" starting point 
to analysing how the circuit behaves if it's not immediately clear to 
me.  My final VA model will be some Assembly or C code but I have been 
known to go via MATLAB models too.  It always mimics the audibly 
perceptible attributes of a given circuit though.

Sure there are much better physically informed digital models for drum 
and cymbal synthesis that produce much more realistic sounds, and can be 
coded directly in MATLAB or C.  But my interest is in circuit modelling, 
and the original thread was about techniques for better understanding of 
analogue schematics.

-Richie,


On 2024-05-18 11:59, Mike Bryant wrote:
> If you're going to generate the signals as WAV files, wouldn't it be
> better to just use Matlab or C++ and produce exactly what you want,
> rather than some simulation of a circuit that produced something that
> probably wasn't quite the same as a real percussion instrument in any
> case ?
> 
> -------------------------
> 
> From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of
> rburnett at richieburnett.co.uk <rburnett at richieburnett.co.uk>
> Sent: 18 May 2024 11:55
> To: Mattias Rickardsson <mr at analogue.org>
> Cc: ackolonges fds via Synth-diy <synth-diy at synth-diy.org>
> Subject: Re: [sdiy] *EXT* Re: Becoming better at understanding
> difficult analog schematics
> 
> You can set the maximum time-step of the simulation to something like
> 2us and save the WAV file at a high sample rate like 192kHz.  Then
> load
> that into an audio editor, band-limit to 20kHz and resample to 48kHz
> before saving.  I find that gives better results for simulations that
> exhibit an inherently "high-pass" response like hi-hats, etc.
> (Another
> thing that helps is to follow the circuit being simulated with a basic
> 1st or 2nd-order 20kHz low-pass RC filter before writing the waveform
> out to a WAV file.  This curtails some of the ultrasonic stuff so it
> aliases less in the WAV file.)
> 
> Good VA has a lot in common with Spice simulations, but it has to be a
> bit cleverer to render in real-time and to handle things like
> non-linearities and discontinuities in a way that doesn't result in
> unacceptable levels of aliasing in the final audio output.
> 
> Being able to export simulation results to WAV audio files is still a
> neat feature though, aliasing and all!
> 
> -Richie,
> 
>> Very useful for prototyping, but it's aliasing like crazy if you
>> produce rapidly changing signals like cymbals etc. The simulations
> are
>> neither band-limited nor having constant timesteps. Virtual analog
>> synthesis is something else. :-)
>> 
>> /mr
>> 
>>> 
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> -------------------------
> 
> From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of
> rburnett at richieburnett.co.uk <rburnett at richieburnett.co.uk>
> Sent: 18 May 2024 11:55
> To: Mattias Rickardsson <mr at analogue.org>
> Cc: ackolonges fds via Synth-diy <synth-diy at synth-diy.org>
> Subject: Re: [sdiy] *EXT* Re: Becoming better at understanding
> difficult analog schematics
> 
> You can set the maximum time-step of the simulation to something like
> 2us and save the WAV file at a high sample rate like 192kHz.  Then
> load
> that into an audio editor, band-limit to 20kHz and resample to 48kHz
> before saving.  I find that gives better results for simulations that
> exhibit an inherently "high-pass" response like hi-hats, etc.
> (Another
> thing that helps is to follow the circuit being simulated with a basic
> 1st or 2nd-order 20kHz low-pass RC filter before writing the waveform
> out to a WAV file.  This curtails some of the ultrasonic stuff so it
> aliases less in the WAV file.)
> 
> Good VA has a lot in common with Spice simulations, but it has to be a
> bit cleverer to render in real-time and to handle things like
> non-linearities and discontinuities in a way that doesn't result in
> unacceptable levels of aliasing in the final audio output.
> 
> Being able to export simulation results to WAV audio files is still a
> neat feature though, aliasing and all!
> 
> -Richie,
> 
>> Very useful for prototyping, but it's aliasing like crazy if you
>> produce rapidly changing signals like cymbals etc. The simulations
> are
>> neither band-limited nor having constant timesteps. Virtual analog
>> synthesis is something else. :-)
>> 
>> /mr
>> 
>>> 
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