There are various audio recorders on the market, you could have stumbled upon one of these or something similar:
|Victure, X5||8GB, 12h,
|stylish and solid (glass+metal)|
|Elegiant, CupGtdQWy||8GB, 16h||bulky and simple design with very long recording time|
|Pendrive recorder||8GB||very cheap, fragile, buggy, small battery, decent recordind time|
some of them can record directly in MP3 format but this depletes the battery faster than the WAV one.
Using the WAV format produces a file not suitable as input of our beloved tools like
opusenc, we can use
mplayer to convert it to a suported format:
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apt install mplayer opus-tools # convert WAV file to a supported format mplayer -vo null -vc null -ao pcm:fast:file=in_ok.wav in.wav # compress the converted WAV file in OPUS opusenc --bitrate 24 in_ok.wav out.opus
you can use the attached
recorder2opus.rb script that uses a named pipe file to avoid the creation of the converted WAV file.
Using the Victure X5 recorder with the lowest WAV quality I made some compression tests in MP3, OGG and OPUS and these are the results:
- File size at the same bitrate: MP3 > OGG > OPUS. So OPUS is the winner.
- A meaningful bandpass range for voice recordings is about 11kHz so we should use an OPUS bitrate between 24-28Kb/s (see reccommended settings). The audio quality remains high in the range 20-28Kb/s but below the 24Kb/s the file size increases. So 24Kb/s is the winner.
- Trying to downmix to MONO always gave a bigger file. So it is better to keep it STEREO.