fuzzyT Wrote: > seanadams wrote: > > That is a really low threshold. > > Is it possible that the new attenuation controls could lower the noise > floor level enough to get around this?
Well this is fascinating - the short answer is yes we can probably make it work. Our noise floor in the audio band is down at -127 dBu. However delta-sigma DACs inherently generate impulses (high frequency content) of some couple hundred microvolts even when fed a DC level - i.e. you trade much higher performance in the audio band for some out-of-band noise. Even for all-zeroes the DAC is actively working to hold the output between two levels. So what is tripping your amp is probably this component of the noise floor. Looking at the rms level of noise floor it is about -60dBu when the DAC is active. I tried setting the attentuation to -64dB (mute) but this apparently does not actually disable the DAC, it's the same as playing zeroes. Next I tried inhibiting the clocks completely, which worked - it goes down to -90dBu, which is the same as the analyzer measures with RCA cables not connected to anything. Next I tried disabling the DAC by setting its reset bit. This worked too. So with some smarts in the SB2 to shut off the DAC when appropriate we should be able to do this. http://www.seanadams.com/sb2_noise_floor.gif http://www.seanadams.com/dac_disabled.gif -- seanadams _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
