Changing file format with less quality reduction

Special Interest Groups Audio Processing
1

I have a sound file with some speak on, and the format of file is 44Khz, 16Bit Mono, PCM

I need the file in a telephone enviroment that only supports 8Khz, 8Bit Mono, CCITT U-Law/A-law.

When i use Windows soundrecorder to convert the file it ends up with a lot of noise in the speak. Is there anyway i can use audacity to convert the file without too introducing much noise like windows sound recorder makes???

(Please bare with me on my english, im not that good at it)

2

You have two problems that are only kind of fixable.

  1. When you convert from 16-bit to 8-bit you will greatly increase the amount of noise in a recording, so unless you have a really clean original file, it’s gonna sound bad no matter what. The only way around this is to get a cleaner source file. You can try re-recording, or using Noise Removal on the 16-bit file before converting it.

  2. Converting down to an 8KHz sample frequency will remove just about all the high frequencies from your audio. With the human voice, you can help this a little by using the Equalizer to boost between 500Hz and 3000Hz. But again, it’s never going to sound great.

Remember, it’s more important to get the speech to be understandable than it is to get the speech to sound good. That’s the most important thing for a telephone signal.

3

I too need to output - or better yet - record using CCITT u-Law as well. Tried both suggestions but the net effect is a poor quality recording.
The best so far (which is a far cry from good) is using sound recorder and setting u-Law first then recording… but then the waveform is not editable in sound recorder at all. So, one is left with areas of the recording that need to be truncated, silenced or equalized but no way to do it unless you import it into a program like Audacity and subsequently exporting and then converting back into u-Law make the whole thing sound like mush!
Having support to record in this format “natively” would be a big plus.
Is this something that could find its way into what is a very excellent product? Maybe into the Audio Track menus?
-dave