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Resampling of low frequency audio podcast

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g.orlandini:
Hi all,

I'm listening a lot to audio podcast with sample rate lower than classic 44100 Hz (it's 11025, 12000, 16000 or 22050). In the Sansa Clip Plus manual I read:
 "7.18. Frequency
This is the sampling frequency used for the rockbox playback engine. Audio at a different sampling rate will be converted to this sampling rate prior to mixing using a cubic Hermite polynomial resampler. Note: For best quality and battery life, select the sampling rate used by your audio.
This is typically 44.1kHz."
So this means a 11025 Hz audio is resampled to 44100 Hz while I listen to it? In case there is a resample, how bad is it for battery consumption and audio quality?
Thanks for sharing your opinions/knowledge

saratoga:
You have to resample with such low rates. The CPU time required is relatively blow, and quality doesn't matter given such low sampling rates.

gevaerts:
One thing to note is that the higher the sample rate of the mp3 (or whatever) file, the more work the CPU will have to *decode* it. This means that while an 11.025kHz file will need a bit of CPU to convert to 44.1 or 48 kHz, that will be swamped out by the actual decoding needing a lot less.

What *may* make a difference in quality is setting the sample rate to a multiple of your podcasts (if possible), e.g. set it to 44.1kHz if you listen to 11.025kHz or 22.05kHz stuff, and set it to 48kHz if you listen to 12kHz or 16kHz files. As saratoga noted though, you're starting with fairly low quality, so I suspect you probably wouldn't hear the difference anyway.

g.orlandini:
Thanks for your answers. If I understand well when I listen to a podcast with sample rate 11025 or 22025 I should set playback frequency to 44100, instead if 12000 or 16000 I should set it to 48000. If playback frequency is a multiple of audio frequency CPU time and quality loss is low. Sometimes I do resample/recode audio podcast to save space in my sansa clip (usually from mp3 2 ch 44100 128 Kbit to mp3 vbr9 1 ch 11025 @ 22-24 Kbit with no big audio quality loss) and I wonder if I the bigger CPU time used to resample from 11025 to 44100 is compensated with the smaller file size and less disk read time.

Thanks again

saratoga:

--- Quote from: g.orlandini on September 14, 2017, 01:07:25 PM --- If I understand well when I listen to a podcast with sample rate 11025 or 22025 I should set playback frequency to 44100, instead if 12000 or 16000 I should set it to 48000.
--- End quote ---

There is no reason to do that.


--- Quote from: g.orlandini on September 14, 2017, 01:07:25 PM --- If playback frequency is a multiple of audio frequency CPU time and quality loss is low.

--- End quote ---

I have no idea why people think this, but it is not true. 

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