As an owner of a GoPro HERO 5 Black I suffer from the lack of documentation regarding “raw audio”:
I can get an MP4 video with stereo sound (“GoPro AVC”) plus an extra WAV file with four mono channels recorded with 32-bit floating point (“pcm_s32le”) at 48 kHz.
As the HERO 5 has only three microphones (according to the manual), I tried to find out the channel mapping by recording a short video while moving a sound source around.
However the WAV file’s recording level is very low:
Much lower than -48dB it seems.
My problem now is:
How can I “preview” the audio wave before trying to normalize?
I could successfully “zoom in”, but that did not help.
How can I see the wave form?
I’m only an occasional user of audacity, so I might be missing something obvious.
Should I “zoom out” instead?
However I’m hitting the -48dB limit and I didn’t find the setting to change it.
Shouldn’t Audacity (2.4.2 is the version I’m using) adjust automatically for 32-bit float resolution?
After normalizing the wave-forms to -20dB, I see this (probably quite some quantization errors):
However the WAV file’s recording level is very low:
Much lower than -48dB it seems.
Try the Amplify or Normalize effect. You might have to Amplify twice because there is a 50dB limit. Floating point can go that low without loosing quality so amplifying is worth a try, but there probably is something else wrong.
If the data is scrambled or decoded incorrectly you’ll almost always get full-volume noise noise so it probably really is that quiet (or silent).
Shouldn’t Audacity (2.4.2 is the version I’m using) adjust automatically for 32-bit float resolution?
Yes. The WAV file header tells the software what format you have. The data is scaled automatically by the software and/or drivers 0dB is the same volume in floating point, 24-bit or 8-bit, etc, (even though the “numbers” are different). By default, Audacity works in 32-bit floating-point “internally” so when you open a file or record it gets converted to floating point (if i’s not already). Then when you play it, the drivers convert it an integer format that matches the bit-depth of your digital-to-analog converter.
Thanks for the response, but what I wanted to do was to “zoom in” until I can see some audio.
The audio is obviously there, while being very silent. Maybe it’s a firmware bug in the GoPro.
I was able to solve the problem, and it looks like a bug in Audacity:
I had changed the the resolution of the playback meter from -48dB to -120dB. The scale changed, but the displayed wave shapes did not.
However when starting Audacity the next time, the wave shapes were scaled from -120dB, too!
