Exported MP3 messed up on some platforms, perfectly fine on others

[gumshoe38]

Hi all, I'm trying to put together my radio show, thus am mixing multiple tracks in Audacity 2.4.2 on macOS Mojave. The audio sounds perfect when I play it in Audacity itself. However, once I export as an MP3 (extreme quality) and try and play with quicktime audio player, the audio is jittery and cuts in and out. When I play the mp3 in iTunes on my mac, it sounds even worse, with harsh/metallic sounds. When I upload to Google Drive and play it on my mac or iphone, the mp3 sounds perfect again! And when I play it on Apple Music on my iPhone, it also sounds perfect. When I import the mp3 back into audacity, it still sounds good.

I'm worried about sending the mp3 to the station, and it sounds bad on the air, given it sounds bad on some platforms but good on others. What's going on?? WAV files sound perfect on most platforms, but I must have it as an mp3 for the station. Converting the WAV to mp3 makes the file sound bad again.

Thanks for any help!

[steve]

Is your show mono or stereo?

[kozikowski]

I'm worried about sending the mp3 to the station

No. Don't do that until we resolve this.

Is your show mono or stereo?

What he said. One blue wave on the timeline or two?

Koz

[gumshoe38]

Stereo

[kozikowski]

OK. Step one. We make a protection backup. File > Export > Export as WAV, 16-bit. Move that file somewhere where you're unlikely to step on it by accident.

Tracks > Mix > Mix and render to a new track.

This should give you your stereo show on top and under that, a single blue wave mono track. Solo that mono track (button on the left) and play it. It should be damaged in the same places that your troubles are damaged.

Let us know. Different fixes depending on how this comes out.

Koz

[kozikowski]

Hold it. I got the numbers wrong.

As we go.

Koz

[kozikowski]

After you make your protection file.

Tracks > Mix > Mix Stereo Down To Mono.

That will give you a single blue wave. Play it and see what's there.

Koz

[kozikowski]

What we expect is that some of the files you used to mix in your show are damaged. In stereo (two waves) this can give you a slightly odd-sounding show (some sounds coming from behind you) but the instant you mix down to mono or play the show on a mono-mix sound system, the broken parts of the show may vanish or turn to trash.

The stupid joke is this only happens when the client gets the work.

If this is it, you get to decide whether you want to try and fix the Edit Master, or go back to the original sound files, fix them, and recreate the show. This isn't fun.

Koz

[gumshoe38]

Aha. When I mixed down to mono, I am now hearing the cutting in/out in audacity.

So, if I'm understanding correctly, one or some of the tracks I am using are damaged, but the problem is only noticeable when the mp3 is played mono? So, the reason the mp3 sounds bad on some platforms and good on others has to do with whether it is being played stereo or mono on the platform (google drive vs. quicktime audio vs. itunes, etc.)?

I guess I will have to get to figuring out which of the tracks are damaged. Is there a way to prevent this in the future — e.g. try importing every track as WAV or something. I also am curious as to why the problem doesn't present when I export as WAV.

Thanks again for all your help, folks.

[kozikowski]

You may be a victim of a convenience. The latest Audacity convert to MP3 also mixes down to mono. It's a little checkmark in the dialog and it defaults to checked.

Any conversion of your stereo show to mono will reveal this problem. File format is irrelevant.

The Left and Right channels of some of your work are put of phase.

If you magnify the damaged tracks, you may see the up and down motion of the waves are exactly out of step.

Screen Shot 2020-09-04 at 14.57.09.png (25.44 KiB) Viewed 221 times

Pay attention who which parts of the show are like that. Music? Only your voice? Something else?

Open a damaged stereo track. Use the drop-down menu on the left > Split Stereo Track. Select the top track > Effect > Invert. Select the top track > Menu on the left > Make Stereo Track. Done. If you magnify the waves again, most of the waves will be going the same direction. This track is fixed.

You can do that to all the damaged tracks and then mix the show again.

Can I predict the past? Did you use a vocal microphone adapter like this one?

viewtopic.php?f=27&t=96907

That one is famous for creating "magic" voice tracks like this.

Koz