VIC Audio - is this correct

[JonBrawn]

Looking at the audio circuit driven by the 6560/1, it looks like there's effectively a low pass filter of 1600Hz or so (R8, C10) - that's way lower than I would have expected, which would have been of the order of 20kHz. Am I missing something?

The internal impedance of the sound output of the chip is about 1kΩ, so with C9 that would be a 16kHz low pass filter, which is closer to my expectation.

[DarwinNE]

I had a look to the schematics and it seems that there were different versions.

Here, there is a RC filter (R9/C12) at the base of Q2 that has a -3dB cutoff probably a bit below 16kHz, that is reasonable:
http://www.zimmers.net/anonftp/pub/cbm/ ... on%20E.pdf

Here, the circuit is different, though:
http://www.zimmers.net/anonftp/pub/cbm/ ... 01-02a.gif
R16-C20 seem to cut quite low (1.6kHz or even less, given the output impedance of the IC)

I think this low cutoff has been used to make the square waves sound less "harsh", after all it is not a very selective filter and I doubt many of the TV of the time could deliver HiFi audio above let's say 10kHz.

Here we have the same filter circuit as above, but with the numbering of components that corresponds to yours:
http://www.zimmers.net/anonftp/pub/cbm/ ... 1027r1.gif

I think the VIC20 with or without the filter would sound different.

EDIT: I found this discussion here on Denial: http://sleepingelephant.com/ipw-web/bul ... er#p110441