Ringing in Conversion from Wav to MP3

[kozikowski]

<<<the world today thinks mp3 is high fi
and anything "better" sounds strange to them>>>

Unless the bubbling gets too bad and then it sounds strange to everybody. Editing is about control. If you do production in a compressed format it gets progressively worse and you have no control over it. You can go down to MP3 from a high quality format, but you can never come back.

Koz

[palmeroo]

Thanks to all for your help with Audacity.

Trebor's guidance on converting to mono before converting solved the ringing problem and should allow us to get adequate sound quality for the lectures in a compact format.

If Palmeroo isn't aware how to convert a stereo track into a mono one on Audacity
"Stereo track to Mono" is on the "Tracks" menu ...

stereo track to mono1.png

Sacrificing stereo will reduce the file size and compression artifacts for a given kbps.

My apologies to all of you audio masters, but these are walk around lecture audio notes for docents at a major metropolitan art museum. The docents understand and appreciate at least the visual arts and want to share their appreciation of real 3D objects and not some over compressed jpeg thumbnail photographs. Most docents have attended the walk through lecture and the mp3 has been a helpful supplement for their training and memory.

We would have continued with the Sony mono recorder but changed to the H2 to please the AV Techs. The H2 allowed direct plug in into the audio system and avoided ruffling feathers with multiple microphones on the speakers . We have had problems getting from the H2 wav format to the size and adequate quality we had been used to with the Sony. Thanks to your help it looks like we now have a workable solution with the H2 and Audacity.

We will probably continue to use the H2 in the wav recording mode. The minimum H2 recording frequency for mp3 is 44 kHz, I believe, and that would be too large an mp3 file. Audacity has been helpful to allow us to edit interruptions and gaps, and normalize or adjust the volume. We just had trouble getting the Audacity mp3 export small enough as a joint stereo file without the mono tip from Trebor.

We had managed to get a satisfactory quality and size by using iTunes to convert the wav file into a mono mp3. But using iTunes would have required us to export the Audacity edits into another wav file to be processed by iTunes.

Staying in Audacity will now more simply give us all we need, even if we have had to sacrifice much of the audio fidelity. Sometimes you just need a peanut butter sandwich to keep going and a five course meal is not needed or useful. Please understand our needs and constraints may force us to compromise audio quality. We would not think of trying to use these files for anything other than a small group of personal users, nor mean to imply the extra bits are not necessary or useful.

Thank you all for your help.

[palmeroo]

Here's some spectral output from the various recordings for a noisy period at 0.2-0.4 sec. The 16000 Hz mp3 conversion of the stereo file shows more spikes which could indicate the ringing. The mono file, suggested by Trebor, shows less structure and is listenable, at least for lecture notes. A signal processing guru colleague suggested the stereo mp3 spikes could have resulted from the channels stored as L+R and L-R. Or is there another explanation?

Frequency Content of Objectionable 16000Hz mp3 stereo conversion

16kbps stereo joint stereo 0.21-0.43s.png (21.96 KiB) Viewed 565 times

Frequency Content of Listenable 16000Hz mp3 mono conversion

16kbps mono joint stereo 0.21-0.43s.png (22.18 KiB) Viewed 563 times

Original wav file spectrum 0.2-0.4 s

original wav file 0.21-0.43s.png (22.19 KiB) Viewed 567 times

[Trebor]

If combining the stereo tracks to mono in audacity is creating a ringing effect, (possibly a comb effect if one mic is further from the lecturer than the other),
then instead of combining the stereo tracks (L+R) to produce a mono one, just discard either L or R track and make the remaining one mono.
e.g. use "split stereo to mono" on your original stereo track then discard one of the two mono tracks produced. If one track is inferior, (quieter or noisier), then bin that one, otherwise delete either one. Clicking on the [x] on the top left corner of a track deletes it, (this deletion is reversible using "ctrl" +"z").

split stereo to mono.png (17.68 KiB) Viewed 551 times