Chaning sample rates mid-recording?

[Macloo]

I see a problem like this ("chipmunk" audio) very often. I will try to describe it carefully and maybe someone here can help -- which would be GREAT!

I teach students in labs with computers that are Windows. I myself use both Mac and Windows. I have never had this problem on a Mac. I myself have not had the problem on Windows, but MANY STUDENTS do experience this problem on Windows! We are all using the latest version (not beta) of Audacity.

1. We play our MP3s through a Flash player. This means the sampling rate MUST be 44.1 or 22.05 -- the other rates (48, 32, etc.) will always sound like chipmunks (speeded up) in Flash. This is a limitation of Flash.

2. We know how to set our preferences in Audacity. I even made a PDF handout that shows the correct settings (http://www.jtoolkit.com/audio/Audacity_Guide.pdf).

3. Students edit their audio and save an Audacity Project. Then they export the MP3.

4. The exported MP3 -- in some, but not all cases -- does NOT HAVE the sampling rate that was set in the preferences!

The exported MP3 will sound fine in Quicktime or Windows Media Player, etc. But because the sampling rate is not 44.1 or 22.05, it is "chipmunked" in our Flash environment.

I have students exporting and re-exporting dozens of times, and still NO LUCK. They keep getting a final sampling rate that is NOT what they set in the Audacity preferences.

I think this might work -- it works for some students, but NOT ALL:

1. Check your settings. Export a WAV (not MP3). Exit from Audacity.

2. Open the WAV. Save As (new Audacity Project filename).

3. Export MP3 from that new project.

If anyone can help with this problem, my students would be very, very grateful to you!!

[alatham]

Macloo, you're a victim of a rather confusing aspect of Audacity. And of the LAME encoder.

The Edit -> Preferences -> Quality tab has two settings, one for "Default Sample Rate" and one for "Default Sample Format" These two settings have no effect on the format of the file you're exporting to. (Yes, this is confusing).

All those settings do is tell Audacity which format and sample rate to record audio at (and convert compressed audio to when importing).

In order to set the sample rate of the file you're exporting to, change the project sample rate. This is done on Audacity's main screen in the lower left hand corner.

In order to set the bit depth of the export file, go to the Edit -> Preferences -> File Formats menu. Here you can change the bit depth of wav files in the "Uncompressed Export Format" menu. This is also where you change the data compression rate of MP3 files. This leads me to my next point:

The LAME encoder does not support higher sample rates at lower bit rates. If you're exporting to low bit rates (lower than 96), LAME will force the sample rate lower than 44.1KHz (this is why your files were unexpectedly playing fast). So if you need 44.1KHz files, you're limited to 96 kbps at the lowest. I'm not sure of the limit for 22.05KHz files (or if there is one). This is not a limitation of Audacity, but a practical limitation built into LAME (because mixing high sample rates and low bit rates will make bad things happen).

Does that cover everything? I think some of these issues have been addressed in the Beta version, but there is still room for improvement, I think.

[Macloo]

Thank you -- this is one of the most helpful replies I have ever received on a support forum!

I will check into this and com back if there are any more outstanding issues.