static noise in raw data only

hello everyone,
i am usin Audacity 2.1.2.
i am trying to fix some m4a curropted files that where recovered from an andrroid phone. in order to find out the files codec data i checked a good m4a file.
what i’ve found out is that when i try to import the good m4a file throe file/import/audio it works just fine (codec: 32 bit float, 44100 Hz, mono), but when i try to import the same file in file/import/import raw data and using the same definition (codec: 32 bit float, 44100 Hz, mono) its just static noise and its about 1/10 of the time of the origin one.
can anyone please help me understand what i am doing wrong?

No telling what Android did to the file format and I don’t have an Android phone to try it.


but what is the reson that i hear it normaly in import/audio and hear nothing but static noise in import/import row data with the same definition?
if it works in import/audio, shouldn’t it work the same way in import raw data?

this is how it looks like’, the upper one is import/media the lower one is import raw data

“RAW” digital audio is simply a sequence of sample values.
Formats, such as WAV and AIFF are basically “RAW” data, with some added “header” data.
“M4A” is a compressed format, where the audio data has been cleverly encoded to reduce the amount of data to a small fraction of its original size.

“RAW Import” is for importing “RAW” data. If you attempt to import an M4A file with RAW import, then the M4A data is imported as if it were RAW data, which it isn’t. Because it isn’t RAW data, the result of importing as if it were, produces garbage (noise). Because there is much less data in the M4A encoding than there would be if it were RAW, there is less track data, ie, the imported track is much shorter than it would be from importing (a larger amount of) RAW data.

…Try compressing a text file to [u]ZIP[/u] format.*

Then, open the “raw” ZIP file in notepad without decompressing it.

I’ve never actually tried that but I’m pretty sure the ZIP file looks like garbage unless it’s properly decoded/decompressed.


  • This is a little different because ZIP is lossless and MP4 is lossy, but in both cases the compressed file is smaller and, of course different from, the original file.

Also, you can’t use Audacity to give you information about bit depth of a file because it converts imported audio to PCM if it isn’t already and by default expands it to 32-bit float. M4A files don’t have bit depth in any meaningful sense.

Probably you want to search for an M4A validation or repair tool. There are some around but you usually have to pay for them, and they could be hoaxware, so check the reputation of the product online before handing over money.