Audacity Forum

Hi

I have a number of .wav files which are too big and I need to decrease them in size. In order to do this I'm happy to reduce the quality. So I take one of my 44kHz wavs, set the project rate to 8kHz and export as wav. I was puzzled to see that the exported file was exactly the same size. When I reloaded it, the sample rate was indeed at 8kHz but the file had been extended by 5 times it's original length by blank audio. This was not really the behaviour I had wanted. I could select the real sample and then save selection but it's a bit of a pain as I have a lot of files to process. Am I doing something wrong or is this a feature - I'm using 1.2.6.

Thanks

Andy

Do you NEED to stay with the WAV format?
You can achieve better quality and smaller file size by using OGG or MP3.

A simple way to halve the file size is to convert stereo tracks to mono.

I would recommend updating to Audacity 1.3 - it's probably more stable and better behaved than the old 1.2.6 "stable" version.

Unfortunately, yes, otherwise I would have switched to mp3. After various experiments it would seem it just miscalculates the output size incorrectly, sometimes adding 20-30 seconds of blank audio on to the file.

Audacity will export your work in whatever sample rate is listed in the little block in the lower left of the work window.

You understand 44100 is the Music CD standard sample rate and it's just barely enough. Anything lower than that and the sparkly, crisp quality of the work will suffer.

You can do enormously better with AAC or M4A for sound compression rather than intentionally damaging the fidelity of the work. AAC 256 (Stereo) is the High Quality level for Apple iTunes performances. M4A is the base technology for Windows Media.

Your decision needs to be made with the destination or client in mind.

Koz

amiles wrote:Unfortunately, yes, otherwise I would have switched to mp3.

I'd be interested to know why you need to stick with WAV format for low quality files.

amiles wrote:After various experiments it would seem it just miscalculates the output size incorrectly, sometimes adding 20-30 seconds of blank audio on to the file.

Could you give a step by step account (as detailed as possible). I want to be able to do exactly the same as you so that I can see the problem for myself.
Something like:
1) Open Audacity.
2) From the Generate menu, select "Tone..."
3)...

(sorry this will be a bit time consuming for both of us, but it may lead us to the root of the problem.
While you are doing that, I'll dig out my old Audacity 1.2.6

stevethefiddle wrote:I'd be interested to know why you need to stick with WAV format for low quality files.

We have a customer that uses PowerPoint 97 for their presentations, I need to produce a presentation for them but that version of powerpoint only supports .wav files. Without reducing the audio quality the file is 100Meg, too big to supply to them. If I cut the quality right down it comes to 5Meg - it doesn't sound as good but I think it's still acceptable as it's just speech.

stevethefiddle wrote:Could you give a step by step account (as detailed as possible).

Sure. It's very simple:

1) Open Audacity
2) File->Open. Load my WAV file (Wav file is 10 seconds long - 44kHz mono 32-bit float)
3) Click Project Rate at bottom left - select 8kHz
4) Edit->Preferences - File Formats - Uncompressed Export Format - Select WAV (Microsoft 4-bit MS ADPCM) - OK
5) File->Export as WAV... Save file under new name
6) File->Open. Load the new WAV file (Wav file is 27 seconds long - 8kHZ mono 32-bit float)

Many Thanks

Andy

amiles wrote:We have a customer that uses PowerPoint 97 for their presentations,

There is a neat trick that allows you to use MP3s in PowerPoint 2007. You just need to add a RIFF header to the MP3. (This may only work with CBR MP3s - there the only ones I've tried) You can create MP3s with RIFF headers using C-Dex which is a really good (free) CD ripper program. Some instructions: http://www.technologytrish.co.uk/pptembedmp3.html

amiles wrote:1) Open Audacity
2) File->Open. Load my WAV file (Wav file is 10 seconds long - 44kHz mono 32-bit float)
3) Click Project Rate at bottom left - select 8kHz
4) Edit->Preferences - File Formats - Uncompressed Export Format - Select WAV (Microsoft 4-bit MS ADPCM) - OK
5) File->Export as WAV... Save file under new name
6) File->Open. Load the new WAV file (Wav file is 27 seconds long - 8kHZ mono 32-bit float)

Ah yes, there seems to be a problem with ADPCM encoding. On the eve of the Audacity 2.0 stable release, this problem is not going to get fixed in Audacity 1.2.x.
ADPCM export works in Audacity 1.3.9 - when Exporting (Click OK on the tag editor window then) select "Other Uncompressed Files" and choose ADPCM from the options.

I'll give that a go. Thanks for your help.

Andy