====== Simulating Analog Audio Cicuits ======

{{wiki:spicesound.png?250  }}

Problem: been reading [[http://linuxaudio.org/pipermail/linux-audio-user/2007-May/045851.html|LAU]]

Idea: feed the //great// [[sf>ngspice|SPICE]] simulator with audio-data.

Solution: add a //libsndfile// voltage-source to SPICE ;)



===== general information =====


<note warning>A new version of the software and this document is now available at [[:oss:spicesound:start|SpiceSound]] </note>

It's yet a quick experiment, and requires patching the SPICE source-code. Initial tests show that it might be realistic to simulate simple schematics in real-time((simulating 1sec audio of the foxx-effect at 48ksps on a intel core P6 1.6GHz takes about 4sec)). Although the spice command is already named ''jack'' it's yet only a file-reader. For testing, there is a tool ''txt2snd'' to convert spice ''.print'' lines into wav files ((txt2snd writes //yet// only 16-bit signed-int-LE wave files)). 

one (of the many) issues is running spice in audio-samplerate time-steps... - **it's work in progress**.

===== prepare =====
  * patch spice: {{wiki:ng-spice-rework-17-sndfile.diff}}
  * compile {{wiki:txt2snd-0.1.tgz}}
  * prepare some libsndfile readable audio file. 



===== spice syntax =====
The patched spice knows a new type of voltages-source ''jack'' with the optional argument ''file''.

an example netlist entry connecting the sound-source ''/tmp/test.wav'' to pin 4(Signal) and pin 0 (GND)  with a range of [-1..+1] Volts looks like:

  V_V2 4 0 file /tmp/test.wav jack 0 0 1.0 0

**Syntax:**
  jack <id> <v_offset> <v_mult> <t_off>
  file <filename>

  * ''<id>''  an integer identifier 0 to 2
  * ''<v_offset>'' offset added in Volts
  * ''<v_mult>'' the multiplier when converting sndfile-float [0..1] to Volts
  * ''<t_off>'' offset in milliseconds added when seeking the sound-file
  * NOTE: The option ''file'' must precede the option ''jack'' to take affect.
  * default files are id=0:''/tmp/test.wav'' id=1:''/tmp/test1.wav'' id=2:''NULL''

===== txt2snd =====

''txt2snd'' allows to convert spice output int wav files - it's yet rather simple but has a built-in help.

It reads 4 tabulator separated values per line in the format:
  <idx/int> <time|ms/float> <ignored/float> <value/float>
example:
  11      8.916652e-05    1.846313e-02    -7.477363e-01

this format can easily be generated by SPICE. in the following example 20 seconds of ''net 5'' are printed at 48kSPS:
  .print tran  v(4) v(5)
  .tran 2.08333e-05 20.0 0 2.08333e-05
  .op

Note: Rounding (spice-milliseconds to audio-sample) is buggy and txt2snd includes an only sometimes working workaround (use ''--verbose'' to investigate skipped/missing frames).

the following script might come in handy..
  #!/bin/sh
  INFILE=example.netlist
  OUTFILE=/tmp/spice.txt
  WAVFILE=/tmp/spice.wav
  echo "# writing data to $OUTFILE"
  ngspice -b $INFILE | awk 'BEGIN{go=0;} /^-------------------------------------/{go=1;} /^[0-9]/{if (go==1) print $0;}' > $OUTFILE
  echo "# txt to snd"
  cat $OUTFILE | txt2snd $WAVFILE
  echo "# done."


====== Example ======

**spice3 sound example **

  V_V2 1 0 file /tmp/test.wav jack 0 0 1.0 0
  R_R1 1 0 1M
  
  .print tran  v(1) v(1)
  .tran 2.08333e-05 2.0 0 2.08333e-05
  .op
   
  .END

Save this example script to ''example.net''; save a 48k wav file to ''/tmp/test/wav'' and launch with ''ngspice -b example.net''. this prints the values (and some spice debug output) to stdout (see script above).
pipe the cleaned spice output into ''txt2wav'' to produce a wav file again (also see script above).

** foxxfuzz **

{{wiki:foxx.oregano.gz}} is modeled after:
  * http://www.geocities.com/CollegePark/Library/1355/tonemachine.gif
  * http://www.geofex.com/FX_images/foxxfuzz.gif

NOTEs: 
  * The simulated Diodes and NPNs are not the original, but the default models available with //oregano//.
  * the gain/sustain pot is modeled in R50/R51 - sum 50k
  * the tone pot is modeled in R60/R61 - sum 50k
  * flip the octave switch, by removing diode D1. w/o Diode = off

Beware: it's not yet debugged... 

Stay tuned for a SPICE netlist and soundfiles, tweaks & screenshots.

** aliki/jace ** 

ToDo - a good way to verify..
  * measure response of a simple circuit and document with aliki (and use in realtime with jace..)
  * compare aliki w/ spice impulse response analysis.
  * compare spice processed audio and jace processed audio.


====== References ======
  * [[http://sourceforge.net/project/showfiles.php?group_id=38962&package_id=31152&release_id=352845|spice source]]
  * http://www-ti.informatik.uni-tuebingen.de/~bernauer/lehre/ti-1-0506/spice/ngspice.pdf