On Oct 30, 2005, at 1:39 AM, Patrick Dixon wrote:
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.
Well, internally on the player, the old volume control and the new
volume control both change the same gain coefficient.
The old-style is a 1.7 fixed-point encoding and the new one is a
16.16. So, depending on the value of the gain, you may find rounding
errors, since the resultant value is truncated at 24-bits, but the
trade off is that you can have much smaller volume increments.
I can't argue that you can't hear the difference (folly in this
forum), but I do believe that it's mathematically correct and for the
vast majority of users the new volume curve is a benefit.
p.s. I found this article on dither very interesting: <http://
stereophile.com/features/705dither/>
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
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