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Digital Volume Control - a different perspective

Posted by cics (A) on January 23, 2008 at 13:18:08

In trying to understand how foobar implements its digital volume control, I prepared some measurement data using the 16/44.1 1kHz 0dbFS test tone (sourced from RME's extreme pure sine (0.001% THD+N) file 0_16.zip). Table (at 16 bit resolution) and associated graph show signal amplitudes at different volume levels. Note for each -6db reduction, signal approximately halves. Only top half of sine waves shown.

Using a volume setting of below -24db and above -50db (for most of my listening), its interesting to see the limited signal amplitude range. At -24dbFS, peak 16 bit signal value is 2068 which translates to an effective 12 bits. The equivalent in 24 bit resolution would be 20 bits.

A perfect digital volume control would produce signal values using double precision as in above table. Decimal value would be lost when translating to actual (16 or 24 bit) samples. This would be its rounding error which at 16 bits gives:

• 0.3db error at -90dbFS
  
• 0.002db error at -24dbFS

Error at 24 bit resolution (ie. upsample 16/44.1 to 24/96) is negligable:

• 0.009db error at -90dbFS
  
• 0.000006db error at -24dbFS

Some questions:

1. Would such digital volume control be superior to analogue variants?
   
2. How does foobar implement VC?

This post is made possible by the generous support of people like you and our sponsors:

Schiit Audio

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