Dealing with low bit rates from Skype call recordings

Audacity 3 Help Forum Windows
1

Hi Team,

I have a problem which I’m hoping you can help me with. It’s related to low bit rates obtained from Skype call recordings.

I am preparting to launch an interview-based podcast, and occasionally some interviews are done over Skype. Information about my setup is as follows:

  1. OS: Windows 10 Home
  2. Call Recorder: Pamela For Skype (Professional license purchased)
  3. Audio Editor: Audacity 2.1.3


    I recorded the Skype call using Pamela, and then edited in Audacity and exported from Audacity to an mp3 (using the standard settings):
  • Bit Rate Mode: Preset
  • Quality: Standard 170~210Kbps
  • Variable Speed: Fast
  • Channel Mode: Joint Stereo

What I noticed is that the outputted mp3 file has a bit rate which is much lower than expected. I am no expert in this area, but my undersatnding is that we want something at least around 128kbps wherever possible. In this context, I have 2 situations I’d like to ask about:

  1. Recorded the Skype call to an mp3 file in Pamela
  • After editing and exporting from Audacity, this resulted in an mp3 file with a bit rate of 84kbps (according to the Details tab after right clicking → properties of the file in Windows)
  • this is fair enough, as it was my fault for recording to the lossy mp3 format in the first place.
  • Having said that - are you aware of any simple ways of getting the quality of the call recording higher?
    e.g.: I tried to export the file from Audacity by bumping up the Quality setting to Extreme 220-260kbps and this increased the bit rate of the output file to 164kbps. However I have no idea whether this is a good thing to do.

    \
  1. Recorded the Skype call to a wav file in Pamela
  • Interestingly, after recording the Skype call to a wav file using Pamela, and editing and exporting from Audacity (using the standard 170~210kbps settings), although slightly better than the above, this still produced sub 100kbps bit rates (92kbps).
  • I was wondering if this was normal? Do people just publish files of this level of quality (for Skype recordings) or am I missing a signficant step somewhere?

Any advice would be much appreciated! I’m learning as I go along, and the ride has been fun (and frustrating at times) thus far!

Many thanks in advance,

Cheers,
Daniel.

2

How does it sound? Is it getting worse re-compressing the MP3?

Lossy compression works (mainly) by throwing-away information. At higher quality/bitrate settings it tries to throw-away details that you can’t hear anyway. If you go to lower quality/bitrates it tries to throw-away the least important information.

The bottom line is, you can’t get that information back or otherwise undo the damage done by lossy compression. The best you can do is avoid multiple generations of lossy compression.

With VBR (variable bit rate) you’re targeting quality so “simple sounds” or silence is encoded at a lower bitrate without damaging quality. Some information has already been thrown-away and I assume it’s “only voice”. That’s why you’re getting a lower-than-expected bitrate even at a “high quality” setting. You can use CBR (constant bit rate) to “force” the bitrate up to 360kbps. You can try that, but it’s unlikely to sound better.

MP3 does some other things besides throwing-away data and the “damage” does accumulate with multiple generations of MP3 compression, even if you encode at the same, or higher, bitrate. (AAC is much more immune to multiple generations of compression, but I don’t know if it helps to transcode between MP3 and AAC.

3

Export Constant Bitrate.

Screen Shot 2020-03-02 at 18.55.00.png
It could be said that you should not be using MP3 anywhere in the middle of production. As DVDdoug above, MP3 gets its small files by cleverly throwing away sounds here and there. If you re-encode an existing MP3, it does it twice. By the time you get to the third time, you can hear the honky, bubbling “bad cellphone” distortion.

The damage is permanent.

Use WAV (Microsoft) 16-bit everywhere including the show master (for archive). Then make the MP3 for posting.

Koz

4

Thanks so much for your detailed responses @DVDdoug and @kozikowski - very much appreciated!

Yes - what you say makes sense. Trying to do anything with the call recording made to mp3, doesn’t seem to make any audible changes - will definitely make sure to double-check that it’s recording to wav!