MP3 Exports in a Chain

I just installed Audacity 2.0.3 and discovered a problem I’d not had earlier. The problem occurs when I try to export a file as an MP3 encoded at 24 kbps. For each file I get a message that the sample rate (44.1 kbps) and the export rate (24 kbps.) are not compatible. I’m offered a menu of suggested export rates and the rate of 24000 bps is suggested. I accept the rate and the export goes as one might hope.

The reason this is a problem is that I generally process many files at the same time. I really don’t want to have to sit waiting to hit the enter key after each file.

Set the default project rate to 24000 (Edit menu > Preferences > Quality).
Close and restart Audacity to check that the setting has taken effect (look in the bottom left corner of the main Audacity window and you should see that the “Project Rate” is 24000.)

You should now be able to run the chain without getting that warning.

Note that 24000 Hz sample rate is not great quality, so when you have finished you will probably want to change the default sample rate back to 44100 in Preferences.


Thanks for the suggestion. I tried it out but unfortunately it did not solve the problem. What seems to happen is that even though I’ve set the sample rate at 22,050, when I load a file either manually or applying a chain the rate jumps back to 44100.

It still does seem odd to me that Audacity has no problem exporting at 24,000 bits per second but it refuses to export at 24 kbps; this suggests to me that the problem might be in the interface with Lame.

The problem is that 24 kbps is too low for 44100 Hz audio.
The files that you are converting have a sample rate of 44100 Hz, so when Audacity imports them the sample rate of the file overrides the default setting in Audacity and sets the project rate to 44100 Hz. Audacity allows files that are imported into an empty project to do this so as to preserve the sound quality of the imported file (the sound quality at 24000 is lower than at 44100 Hz).

Unfortunately I don’t think there is a simple way to achieve your unusual combination of requirement in Audacity.
The options I see are:

  • Don’t use Chains, or use Chains but be there to click “OK” each time you are prompted to change the sample rate.
  • Start off with files that are at a lower sample rate (24000 Hz)
  • Use a higher bit-rate for the MP3s that supports 44100 Hz sample rate
  • Use Audacity with an external command line encoder
  • Use a different program for the batch processing.

Of these, the last one is the easiest option if you only want to batch encode. I would recommend “LamedropXPd” which is a free batch encoder (available here:

If you need to do additional processing in the chain, then using an external command line encoder with Audacity will be the answer. If you need to use this option and need help with it, feel free to ask.

Honestly, I’m not sure what the sampling rate is on the files that I start with - I’m sure it varies from one file to another but I’d be very surprised if they are all sampling at 44100 because none of them require such a high sampling rate - all are simple speech files but they tend to be coded wastefully. But even if they happen to be sampled at that rate, down-sampling to a lower rate is a process that is well understood and is taught in every beginning DSP course; there is absolutely no technical difficulty in performing such a conversion and it at least appears that Audacity does this when asked.

The whole purpose I have in editing these files is to reduce the bit-rate and retain good intelligibility. In older versions of Audacity I was able to do this using a chain that operated without my constant assistance. Perhaps you could point me to where I might download one of these older copies of the program.

Problem solved - sort of.

It turns out that when I change the mp3 bit rate to 32k the chain executes without stopping to ask anything. The resulting file is a little larger, at least some times, but the size is certainly something I can live with.

As a suggestion, it might be useful in writing chains if there were a down-sample (or re-sample) command available. There is such a command when operating Audacity manually, but not one available for use in a chain.

I’ve added your vote to this feature request:

Export sample rate > (20 votes) This is important for MP3 and other compressed formats because if a file imported for batch processing switches the project rate to something not supported by the export format, the batch comes to a halt at the resample dialogue.

We’ll add your vote for that. We’re aware of the problem and it would have been fixed by now if we had more programming resources than we do right now.