> It's not clear that there is an issue at all. We'd need a > reproducible case.There is definitely an issue, and it's easy to > demonstrate/reproduce - the only question is whether you can hear it or not! I say I can, and jhwilliams has done blind testing which indicates that he and his girlfriend can too. I have now reverted to Firmware 15, which I'm happy with sound-wise.
The issue is that previously the volume control used an 8-bit multiplier coefficient which meant that the full resolution of 16-bit audio (which is of course what CDs are) was always retained within the 24-bit datapath of the SB2. The new log volume control uses a 16x16 bit multiplier which means that rounding errors are 'always' introduced, and these are unconcealed by the addition of any dither. It's surprising to me too that I can hear these artifacts, but I think it's the character of the noise (coupled with oversampling in the DAC?) that makes it stand out. Even with the addition of dither (which may well be useful for the replay gain situation anyway), there is an audiophile arguement that says you should always preseve the S/N ratio of the original 16 bit signal where you can. Therefore I am simply suggesting that you 'tweak' the coefficients of volume control settings 20-39 to use 8-bit resolution rather using the full 16-bit resolution of the new multiplier. Much below vol 20, 8-bit coefficients are not enough to resolve the volume steps required, but at these levels the artifacts are unlikely to be an issue. My calculations gave something like this below - so the volume changes would be negligeable with the adjusted coeffs. Just ANDing the 20-39 coeffs with 1100hex would probably give acceptable results. vol 8-bit coeff 'new' dB 'old' dB 20 14 -25.2 -25.4 21 16 -24.1 -24.1 22 18 -23.1 -22.8 23 21 -21.7 -21.6 24 25 -20.2 -20.3 25 29 -18.9 -19.0 26 33 -17.8 -17.8 27 38 -16.6 -16.5 28 44 -15.3 -15.2 29 51 -14.0 -14.0 30 59 -12.7 -12.7 31 69 -11.4 -11.4 32 80 -10.1 -10.2 33 92 -8.9 -8.9 34 107 -7.6 -7.6 35 123 -6.4 -6.3 36 143 -5.1 -5.1 37 165 -3.8 -3.8 38 191 -2.5 -2.5 39 221 -1.3 -1.3 40 256 0.0 0.0 -- Patrick Dixon www.at-view.co.uk _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
