If I export from Audacity 2.0.6 to M4A, with the option set to 500 quality, and using FFmpeg 2.2.2, then the sound quality is awful with a bubbling type noise throughout. Export to MP3 or AIFF sounds just fine. The original WAV files, and the edited WAV files, also sound fine when played back through audacity. Can anyone give me a pointer on what might be going wrong? (Both audacity and FFMPEG installed today on Mac Mavericks).
My export default for M4A is 40. Try that once to see what happens. It’s remotely possible that FFMpeg isn’t following the Audacity settings and you’re actually getting a really low compression instead of Highest Possible.
From the Audacity 2.0.6 release notes: Missing features - Audacity Support
M4A (AAC) exports: > The Quality Slider in “Specify AAC Options” has no effect if the FFmpeg library is built with the libvo-aac encoder, as are recommended builds of FFmpeg for Windows and Mac OS X. > Workaround: > Given the alternative AAC encoders for FFmpeg have other problems as described in these notes, you can instead export as WAV and convert to AAC in iTunes on Windows and Mac.
Or, export M4A from Audacity using “Custom FFmpeg Export”. Click the Options… button, choose “mp4” in the formats list and “libvo_aacenc” in the codecs list, then set bit rate in bits per second. Up to 320000 bps (320 kbps) is supported.
The release notes for the upcoming 2.1.0 release will also mention the “Custom FFmpeg Export” workaround.
Thank you everyone for your replies. The option of converting into AAC using iTunes does the job. I also tried the custom FFmpeg export but could not get the resulting file to play - probably my lack of knowledge of what to put within the options available. I’ll stick with the iTunes workaround.
Given that your target player is iTunes I wouldn’t regard doing this task in iTunes as a “workaround”.
I also use iTunes/iPod and my preference has always been to export WAVs from Audacity and let iTunes do the AAC conversion work, partly because AAC is Apple’s native compressed format and therefore I tend to want to use their conversion tool.
Also this way I get a nice set of WAVs that I can backup/archive to my pair of external USB disks.
I exported 256 kbps stereo and 320 kbps stereo M4A files using Custom FFmpeg Export and iTunes 18.104.22.168 64-bit and 22.214.171.124 64-bit played them.