FS#10906 - Sansa AMS: use PLL B for higher audio sample rate accuracy
Opened by Bertrik Sikken (bertrik) - Sunday, 10 January 2010, 15:37 GMT
Last edited by Bertrik Sikken (bertrik) - Friday, 05 November 2010, 09:29 GMT
There was some discussion recently on #rockbox about how accurate our audio sample rate is for AMS sansa targets, compared to the OF. This patch enables PLL B and uses it for the audio clock, resulting in higher sample rate accuracy (0.04% error). I already committed a change to make the audio clock selection more flexible, so the patch is really small.
In the current situation we use a 248 MHz PLL clock, which gives about 0.15% error. For reference, Wikipedia (
http://en.wikipedia.org/wiki/Pitch_%28music%29#Perception_of_pitch ) mentions a just-noticeable difference of 0.36 Hz at the 1-2kHz octave, which is 0.036% at 1 kHz.
A disadvantage is that the now-enabled PLL consumes 2.5 mW typical (according to the AS3525 datasheet).
Friday, 05 November 2010, 09:29 GMT
Reason for closing: Rejected
Additional comments about closing: An error of 0.15% is good enough for me. This patch did turn out to be useful in the end because it was *really* needed for the AMSv2 players.