Support and General Use > Audio Playback, Database and Playlists
Pitch error in 48kHz mode
asymsucon:
When my Clip+ runs in 48kHz mode, 1kHz sine is outputted as 1.007kHz, in AB test very noticeable difference. In 44.1kHz, it's almost dead center on 1.000kHz.
This is a bit unfortunate as 99.5% of my music collection is in 48kHz sampling-rate and running Clip+ in 44.1kHz could impact quality and battery life.
Issue spotted on firmware ac0fc74
Mihail Zenkov:
I look at code: to get more precision 48 kHz we should switch main frequency (PPL) when we switch from 44.1 to 48 and back. It bit tricky but possible.
Just curious: why all your music in 48 kHz?
asymsucon:
I'm using Opus as my primary lossy compression codec and Opus runs only at 48kHz.
One of the reasons why I opted for purchasing Clip+ was Opus support (no other non-Rockboxed player claims support) so that I could fit in my entire collection at 140kbps onto 64GB microSDXC without any subjectively perceivable audio degradation ;)
Mihail Zenkov:
Ok, I got your point.
But you got resampling from 44.1 to 48 - probably with minor sound degradation but ...
With 48 kHz your runtime from battery will be less for ~8%.
Opus by itself consume to much cpu and your runtime from battery will be significantly less.
asymsucon:
Yes, opus resamples everything to 48kHz during encoding, so some resampling degradation can be expected, however most if not all of it would be inaudible or below 16bit noise floor.
Decoding of 140kbps Opus should run at about 550% realtime, which is not that far from 680% for Lame-320 or 660% for AAC-LC based on tests on 18fecd9 (https://www.rockbox.org/wiki/CodecPerformanceComparison#Sansa_Clip_43_40ARM9E_41
So in the end the CPU power required, while higher shouldn't contribute too much to the battery runtime.
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