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M4A files (Foobar2000/NeroAacEnc) play at double speed

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madsic:
Thanks to the both of you for promt replies. I didn't immidiately figure out how to convert 22kHz to 44 in Foobar2000, so I tried a 44Khz MP3 instead and the M4A conversion plays very nicely (I tried playing the file on winamp alongside rockbox and they kept apace).

To Lear: I'm unable to find what you're referring to. I've looked under converter settings in Preferences as well as 'Encoding Preset', 'ReplayGain processing' and 'DSP Processing' in the Converter Setup (the window you get when you start a conversion). Can you point me i the right direction?

EDIT: I found and did "Optimize MP4 Layout" on the converted file. Didn't change anything that I can observe. I'm no expert but Llorean's explanation makes sense. If you're stille interested, I've uploaded an example here.

Llorean:
Lear: I know that midi plays double speed because the 22050hz isn't resampled and so plays as if it were 44100 and sounds double speed, and Doom suffers the same problem (again because it's using midi), and I'd been told that the iPod simply wasn't resampling at all (though this may have changed, it was quite some time ago)

Lear:
Llorean: Ah, I didn't know what the resampling problem was. But I left out one detail from my explanation: If certain parts of the metadata reader sees a frequency of less than 24k, it doubles the it, in this case making Rockbox see it as 44.1k (the decoder doubles the frequency if the file really is SBR).

madsic: It's not in the settings at all. Try right-clicking on the file. I think it's in the utils submenu (can't easily check right now)...

Lear:
I removed the automatic frequency doubling, so 22 kHz files should play with the proper speed now. The SBR detection was improved, so that the SBR test files I have still work (apart from not playing in real time on most Rockbox players, that is).

However, this might mean that other (SBR) files play at the wrong speed...

saratoga:

--- Quote ---The SBR detection was improved, so that the SBR test files I have still work (apart from not playing in real time on most Rockbox players, that is).

--- End quote ---

Does the SBR actually get decoded?  Or do you mean that the LC part runs slow?

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