[LAD] simulating analog audio devices

Robin Gareus robin at gareus.org
Fri Jun 1 15:19:23 UTC 2007

Pieter Palmers wrote:
> Robin Gareus wrote:
>> Erik de Castro Lopo wrote:
>>> Robin Gareus wrote:
>>> When Spice loads the libsndfile component, can the component find out
>>> the inter-sample period used by Spice? 
>> no. Spice does not use a constant interval; else it would be straight
>> forward to use libsamplerate.
>>> If the above is not possible, I suggest that you up sample the audio
>>> by say 128 times and then linearly interpolate to get whatever inter
>>> sample values you need.
>> sounds like a great idea.
>> I should do that with the output too, but it's a little more complex
>> there: In the beginning I've tried to take the average for all the
>> "spice"-samples matching the corresponding audio-sample. I've only tried
>> that up to 1/(4*Fsample) and it gave much worse results than just taking
>> the closest sample...  - combining interpolation and resampling could be
>> the solution.
>> now that I've got the framework, I'll dig into the details..
> Since you're patching ngspice anyway, maybe introducing a fixed-timestep
> behavior into ngspice is easier? IMHO it's the 'correct' solution (cfr
> other mails).

I have not dug that deep into ngSpice - but from what I've gathered
every instance can modify the time-step depending on different
conditions for each element during the simulation. -  That would be a
reason to implement the audio-sink as element (or model) rather than
'print' command..

ngSpice too interpolates points during a transient analysis, and a 1st
order might be the best one can get anyway.

gnucap might have been the better choice. - When I started, I thought
it'd be a nice /afternoon/ project to fire up SPICE. yawn. - I'll try
upsampling and interpolating input-samples and the reverse on the output
-  but else I'm heading back to the drawing board.. and other endeavors.

more later, gotta run now.

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