Audacity Forum

Hello community!

Thank you for taking the time to read my post.

- Audacity v2.0.0
- Windows 7 Ultimate (x64)

Today a friend of mine came to me with a CD filled with .wav files (there are 6 in total) that are a recording of some company presentation from a few years back claiming that she couldn't open them using Windows Media Player and wanted to see if I could figure out how to get them to work properly. The first thing I tried was VLC, no luck. I then noticed that the files seemed extremely small (varying from 28KB to 1,169KB in size). I decided to do some research and found I could import as raw into Audacity and see what I could do.

After renaming the largest file with the extension of .raw (not that it mattered) and messing around with some of the import settings, it was obvious that this was some sort of audio file. It is short, has a high amount of static, and if imported as mono you can bearly make out the distinct sound of someone talking EXTREMELY fast. It sounds like the rate at which the person may be talking is sped up some thousands of times faster than normal. I have tried to slow down the audio and screw around with the start offset, but that doesn't help.

So I guess my question is; has anyone encountered anything like this before? It seems as if maybe the audio file was compressed? Does anyone have any leads to figure out how I may be able to restore it to the point of it being audible again?

Thank you for taking the time to read my post,
-SunDry

The chances are outstandlingly good that they're not WAV files. You should change Windows so it stops hiding filename extensions. This will go a long way to telling you what you actually have.

-- Hidden File Extensions
-- Start > My Computer > Tools > Folder Options > View > [ ] Hide Extensions for Known File Types (deselect)
-- Apply (to this folder) or Apply to All Folders
-- OK

Then, after you find out that the files are really AAC or M4A (or something like that) compressed files, you should be able to open them with Audacity after you install the FFMpeg software extension/plugin.

http://audacityteam.org/download/

Koz

It could be some sort of ADPCM. ADPCM is a compressed format, optimized for speech. A very popular format for recorded messages in telephony and other communications systems. A common sampling rate is 8000Hz, which would give you the speeding effect at playback you have encountered if your project rate is e.g. 44100Hz. There are many different types of ADPCM, I think the most common is VOX ADPCM.

--
Ragnar

It could be some sort of ADPCM.

Does FFMpeg manage ADPCM files?
Koz

Yes, FFMpeg seems to be able to handle a bunch of ADPCM variants. http://ffmpeg.org/doxygen/trunk/adpcm_8c.html

I can't check right now because I'm sitting at an Audacity-free (aka "work") computer, but if I remember correctly the last entry in Import-RAW... is VOX ADPCM.

--
Ragnar

@SunDrySix: Maybe you could attach a short(!) file to a post here or upload it somewhere so we can have a look at it?

Audio file formats are identified via byte sequences inside the file and not by the file extension like .wav, .raw, or similar. If they are really sound files then they contain any form of compressed data, for uncompressed data the file sizes are too small. But it's virtally impossible to tell what it is without looking into such a file with a hex editor. Maybe we can find a way how you can open the files and convert them into any "normal" audio file format.

- edgar

edgar-rft wrote:@SunDrySix:
Maybe you could attach a short(!) file to a post here or upload it somewhere so we can have a look at it?

I'll second that. Please upload a file we can have a go at.

edgar-rft wrote:Audio file formats are identified via byte sequences inside the file ...

Many (most?) ADPCM file formats cannot be identified by their content. ADPCM files are often completely header-less and only contain the compressed audio. If you don't know the sampling rate, number of channels or bit depth you have to guess.

--
Ragnar

ragnar.jensen wrote:...the last entry in Import-RAW... is VOX ADPCM.

Ragnar,
In my install of Audacity v2.0 on Windows 7, the File > Import > Raw Audio... command gives me only "All files (*)" in the drop-down selection of the "File Open" dialogue window.
Peter

PGA wrote:File > Import > Raw Audio... command gives me only "All files (*)"

You must first click on a file and import it, only then appears the window where you can chosse ADPCM (among other things).

I just wanted to follow up on this, Ragnar was spot on. It ended up being a conference phone recording and once I imported as VOX at 6000 Hz it was audible again! The audio runs into high ringing noises every once in a while, but it seems good enough for what my friend wanted.

Problem solved!

Thanks for the help community!

-SunDry