Filter brewing for the Soekris R2R

These are done using the impulse test function of Fuzzmeasure?

What are the traces in the HD charts? Frequency response is fairly obvious but what about the two around -100dB range?

Apologies. Is second to 10 Khz and third harmonics up to 8 kHz. Yes Fuzzmeasure program. Measures has made after having several hours on. And for every picture I made a 5-6 measures 3 logsweep 10 seconds each to check out always see similar.
 
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The ultimate goal would be a DAM-simulator for the digital output, taking also in account the fixed point arithmetic in the FPGA. To an certain extend this could be done, but at some point we would need implementation details of Soren.


This would make the filter development process much more accurate and efficient.....Fantastic if you can do this!
Thanks
Derek.
 
The full amplitude NOS filter problem could be related with the "problem" of the DAM of handling the maximal alowed negative ampltude.

... @ Soren:
There problem with how the DAM handles the maximal negative sample in the PCM data.
Lets say we use 24bit. According the WAV/PCM specifications the negative numbers are the two-complements and x80 00 00 is the the maximal allowed negative number. The DAM (USB-Amareno) reproduces this a zero. x80 00 01 gives the maximal negative spike.

So you could say there is some extreme clipping for just one value of the amplitud (the max negative one).
This applies to the amplitude after filtering. So the direct correspondence to the PCM aplitude is only given with the bypass or NOS filter.

With 32 bit data high negative amplitudes such as x80 00 00 01 seem to be truncated to 24 or 28 bit and thus lead also to no impuls instead of a maximal negative impulse.

This is probably due to the fact that the natural signal range of a sign magnitude DAC is +2^n-1 to -(2^n-1) and that the allowed range in PCM data is +2^n-1 to -2^n, and some "special case" handeling is missing in the code.

Soren promised a fix of that with the next firmware.
 
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The clipping seems to occur on both positive and negative maxima. Would truncating the negative only have this effect?

My comment was thought as possible explanation of the higher distortion of NOS 0dB plot in the second PDF.

I am quite sure, the obvious clipping of the square wave with the added small sinus should be no "fault" of the DAM but just an effect of the filter+gain, i.e. the (digital) signal after being filtered and gain adjusting contains values above the maximum allowed digital signal which then are "clipped" to the maximum (as nothing higher can be handled by the DAC ladder).

You should be able to see that also with sox, applying there the filters and gain, clipping should be reported.