Big loss of quality when exporting to mp3

Audacity 3 Help Forum Windows
1

I have a problem that’s driving me nuts. I’m recording intros and outros for podcasts. I’m recording voice-overs on Audacity and mixing them with imported mp3s. I get a good sound and mix and export to mp3, but the sound is quite degraded when played back. (Generally a big boost of treble and loss of bass, as well as other artifacts.) If I open that mp3 up in Audacity, it looks a lot different than what I created, with lots of clipping.

I understand that mp3 is lossy, but this is a jump from pretty good to unacceptable just from the export/conversion.

Any ideas? Thanks.

Dan

Windows 7/64
Audacity 2.0.5

2

I’m recording intros and outros for podcasts.

For the last 24 hours, or you’ve been doing this since 2012 and it just started doing this?

I get a good sound and mix and export to mp3

I’d probably start by exporting to WAV and see if the same thing happens. If it does, that clears all the MP3 multiple conversion and compression tools.

I understand that mp3 is lossy,

No. MP3 problems are very simple and easy to recognize with one ear closed. This is something else.

Are you in mono the whole way? Are you trying to mix downloaded stereo music with your mono voices-over?

Do you use the little sliders to the left of your tracks to achieve volume balance and graceful presentation?

It’s a common problem that you can’t tell what the final show balance is going to be while looking at all the different tracks on the timeline. In particular, knowing when you’re going to get overload is something of a magic act.

There is Tracks > Mix and Render that I have never used. I want it to smash all my tracks into one track so I can examine it, but I think the last time I tried to use it, it doesn’t do exactly that.

http://manual.audacityteam.org/o/man/tracks_menu.html

It bothers me that the tonal balance of the show seems to go into the bin. That points to a non-normal problem, or a tool or process you’re using in an odd way.

Does it sound OK if you just record your voice: “Testing one, two, three” and export it? No other tracks, no other filters or effects? There are lots of ways to mess up mixing performances and existing tracks, but most of them are apparent on the timeline right away. They don’t wait to kill you later.

Do us a favor and try to hit all the questions. Too many people ignore everything but the last one.

Post a sample of voice and music on the forum. You can use MP3 so you can get quite a lot in the post. We don’t need the super high quality of WAV for this. No mater what for format, you still can’t post hours and hours.

https://forum.audacityteam.org/t/how-to-post-an-audio-sample/29851/1

Koz

3

What bitrate or quality setting are you using? The best constant bitrate for MP3 is 320kbps, and the best variable bitrate quality setting is ‘V0’.*

With higher compression (lower bitrates) you are getting smaller files, more data is thrown-away and you get and more quality loss. At higher bitrates, the compressed file should sound identical (or almost identical) to the original, depending on the program material.

I’m recording voice-overs on Audacity and mixing them with imported mp3s.

The imported MP3 has to be decompressed before it can be edited in Audacity. If you re-save (re-export) as MP3, you are going through a 2nd lossy compression step. The quality loss can build-up, but at high bitrates the additional quality loss shouldn’t be terrible. Ideally you’d compress once if you want a lossy format, but sometimes you don’t have a choice.

If I open that mp3 up in Audacity, it looks a lot different than what I created…

With lossy compression every sample (i.e. 44,100 samples per second) will be different, but overall it shouldn’t look that different.

…with lots of clipping.

That’s probably normal and probably not a problem that you can hear. Lossy compression does change the wave shape, and some peaks are increased while others are decreased. If it’s a problem, you can try using the Amplify effect to set the peaks at -1 or -2dB before exporting. But as far as I know this slight clipping never creates audible compression artifacts and reducing the volume before compression never makes compression artifacts go-away.

And in fact, the MP3 may not actually be clipped. MP3 is not hard-limited to 0dB like “regular” WAV files, or CDs, etc. Your digital-to-analog converter is hard limited to 0dB, so if you play an MP3 that goes over 0dB at full “digital” volume your DAC can clip.


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  • Many times a lower bitrate or lower quality setting will sound identical to the compressed original. It depends your ability to hear MP3 artifacts and the program material (some material is easier to compress than other material)… If a 192kbps MP3 sounds identical to the original, we can’t say 320kbps is “better”. Or in some cases there may be compression artifacts in the 320kpbs file, and a 192 or 256kbps file is no worse.


    P.S

…and mixing them with imported mp3s.

…with lots of clipping.

Mixing is done by addition (summation). If you mix two normalized/maximized sounds you will get clipping. If you are actually mixing sounds, you may need to reduce the volume of both tracks before mixing.

4

All that is grand and expected. Now account for this:

(Generally a big boost of treble and loss of bass, as well as other artifacts.)

I would guess someone recording voices-over and recording What My Computer Is Playing instead of My Microphone could get that. Depending on the configuration of the computer, that would destroy the music. But the damage would be obvious by playing the timeline before Export.

Having File > Export destroy the music is the wild card in this posting.

Koz

5

Thanks for all of this - I have a lot of experimenting to do.

My (limited) experience in recording is from years ago with analog equipment. I’m a musician who plays by ear, and I was trying to play this by ear too. Time to do some studying…

6

If you’re trying to overdub new music or voices over an existing track, you should be using strict Overdubbing settings.

http://manual.audacityteam.org/o/man/tutorial_recording_multi_track_overdubs.html

Sorry this is a bit overwhelming but we have to account for many different setups.

Please note that the settings you use to record internet audio will cause Overdubbing to fail. Recording “Stereo Mix” instead of following Overdubbing instructions has the effect of leaving the tape key open on the mixing desk while you’re making a second and third pass. I don’t know if you’ve ever done that, but you get audio chaos petty quickly.

Koz