Rockbox Technical Forums

Support and General Use => Hardware => Topic started by: g.orlandini on March 11, 2017, 03:37:12 AM

Title: VBR vs CBR mp3 files battery consumption on Sansa clip+
Post by: g.orlandini on March 11, 2017, 03:37:12 AM
Hi all,

I've noted an higher (+10-20%) battery consumption using VBR vs CBR mp3 files at the same low average bitrate (around 25-30 kbps for VBR and 24 kbps for CBR). If I check also the remaing battery level I see it is changing every few seconds, oscillating up and down a few percent. Is it so much more CPU demanding VBR than CBR?
Title: Re: VBR vs CBR mp3 files battery consumption on Sansa clip+
Post by: saratoga on March 11, 2017, 11:02:50 AM
Shouldn't make any difference.
Title: Re: VBR vs CBR mp3 files battery consumption on Sansa clip+
Post by: g.orlandini on March 12, 2017, 12:54:25 PM
I've checked battery level on a 3 hrs podcast (12% CBR vs 14% VBR), maybe measurement was not accurate enough. Thanks for sharing your knowledge.
Title: Re: VBR vs CBR mp3 files battery consumption on Sansa clip+
Post by: saratoga on March 12, 2017, 01:02:40 PM
That isn't remotely accurate. We have a battery bench mark plugin that can precisely measure battery life while decoding different formats. You can use that, although I wouldn't bother testing different mp3 files against each other.
Title: Re: VBR vs CBR mp3 files battery consumption on Sansa clip+
Post by: asymsucon on March 13, 2017, 01:42:42 PM
When in doubt, check System > Debug > CPU Frequency and see whether CPU is bumped to 192MHz during playback. With MP3s it should always stay at 38.4MHz, same with FLAC.
Battery indicator, as stated, isn't very accurate.
Title: Re: VBR vs CBR mp3 files battery consumption on Sansa clip+
Post by: wodz on March 14, 2017, 06:32:16 AM
... taking into account that gui interaction makes cpu boost.
Title: Re: VBR vs CBR mp3 files battery consumption on Sansa clip+
Post by: g.orlandini on March 14, 2017, 12:13:26 PM
When in doubt, check System > Debug > CPU Frequency and see whether CPU is bumped to 192MHz during playback. With MP3s it should always stay at 38.4MHz, same with FLAC.
Battery indicator, as stated, isn't very accurate.

Yes, I checked the CPU clock and it was 38.4 MHz, it boosted shortly at 192 MHz because of gui insteraction as reminded by wodz.

... taking into account that gui interaction makes cpu boost.

Thanks again for sharing