Help recovering PCM audio!

Hi, I have two audio files in PCM format that were recorded on an old Rave MP mp3 player back in 2000 that are pretty important to me. I couldn’t open it directly or with the ffmpeg libraries. I tried for quite a while messing with options in Import > Raw Data. My results were pretty bad, I could get a somewhat usable quality on one and very very poor on the other.

The mp3 player apparently had 3 quality options (low medium and high). From the file details I can see one has a bit rate of 33kbs and the other 66kbs, which I assume correspond to two of those quality choices. I can also see the length of the audio from the file details so I know how long it is supposed to be, which helped me pick appropriate encoding and sample rate combinations to test.

Does anyone have any advice or experience in trying to convert unknown PCM files to good quality audio?

That’s a contradiction. “MP3” is not “PCM”.
Why do you think it is in PCM format?

Those are both far too low for PCM audio. Typically PCM will be 705.6 kb/s (mono) or 1411.2 kb/s (stereo).

I don’t understand your question, and honestly I have 0 knowledge of audio formats. I didn’t say the 2 files were mp3. The device played mp3s but also had a voice audio recording feature and this feature created PCM files. I’ve done some research on these and my understanding is the lack of a header makes it difficult for applications to know how to process them properly. I tried a few applications and Audacity has been the closest to getting me some usable results.

My question is still regarding recovering this PCM audio. I have tried like 50 combinations of various encoding formats and sample rates using the Import > Raw data feature. Again, the only “clues” I have are what it says in the file properties on Windows which is the 66kbs or 33kbs bit rate (only helpful to show me that they were most likely recorded in different quality levels on the device), along with the audio duration.

So with all that said you did provide some interesting information. If a PCM is 705.6 or 1411.2kbs does that help me find a setting on the Raw Data import? Are there custom encoding methods that can be loaded? I tried every single one that was available. Is it the case for PCM files that it is simply trial and error to get these to work, until you find the right settings to convert them to a more common format?

I know. You said they were “PCM”, but they are probably not PCM. They are probably some sort of compressed audio format (but we don’t know what format).

If they were PCM, then it would be fairly straightforward to import them into Audacity using “Import > RAW”. As you have discovered, you are not able to import meaningful audio using “Import > RAW”, and that’s most likely because the files are not PCM.

Try testing the files on this web page. It may give some useful information about the files: MediaInfoOnline - MediaInfo in your browser

I have are what it says in the file properties on Windows which is the 66kbs or 33kbs bit rate… I can also see the length of the audio from the file details

Windows wouldn’t “know” anything about a headerless file. So that’s a good sign and hopefully MediaInfo can tell you something.

I assume you can’t play the file on your computer? And you no longer have the Rave player?

In case you don’t know this, kbps is kilo_bits_-per-second and there are 8 bits in byte. So you can divide by 8 to get kilo_bytes_-per-second for the relationship between file size and playing time.

Here are the results for the two files… I can’t open them in any audio player. I do have the rave player, but there is some old style SD card it takes which I no longer have, and it has some really outdated PC connector port cable that I don’t have/recognize.

MediaInfoOnline provides this info. Searching for the codec info I actually found this which is very similar to my issue. Thanks for the help so far, if anyone sees anything in this that might help more let me know and I’ll keep playin around with it.

Complete name : MAY07125054.PCM
Format : Wave
File size : 10.8 MiB
Duration : 22 min 42 s
Overall bit rate : 66.2 kb/s
FileExtension_Invalid : act at9 wav
Format : Dev
Codec ID : 350
Codec ID/Hint : Micronas Semiconductors, Inc.
Duration : 22 min 42 s
Bit rate : 66.2 kb/s
Channel(s) : 1 channel
Sampling rate : 16.0 kHz
Stream size : 10.8 MiB (100%)

Complete name : MAY07131521.PCM
Format : Wave
File size : 26.2 MiB
Duration : 1 h 50 min
Overall bit rate : 33.1 kb/s
FileExtension_Invalid : act at9 wav
Format : Dev
Codec ID : 350
Codec ID/Hint : Micronas Semiconductors, Inc.
Duration : 1 h 50 min
Bit rate : 33.1 kb/s
Channel(s) : 1 channel
Sampling rate : 8 000 Hz
Stream size : 26.2 MiB (100%)

It says it’s a Wave file so try changing the file name to MAY07125054.WAV. I’m not too optimistic but it’s worth a try…

I’m not familiar with the “Dev” format. I got a few hits when I searched but no “quick answers” about how to decode it. There are a few more format details that you can search…

I can’t open them in any audio player.

Do you have [u]VLC[/u]? It can play “almost anything” and if you can play it you can re-record it while it’s playing. (Or VLC can convert to a regular WAV file but I’ve never used that feature.)

It seems that it is a proprietary format, unrecognized by MediaInfo.
I’ve done a quick search on Google, and found many other people having the same problem.

Unfortunately it seems that Rave-mp went out of business many years ago, and even when they were in business there was virtually zero customer support.

If you have the original CD that came with the device, there’s a chance that it may contain an app to convert the files into a recognizable format. Other than that, I think it’s unlikely that you will be able to recover the audio.

As DVDdoug suggests, you could see if VLC can play it - I think that’s a long shot, but worth a try.

Yea I had previously tried .wav and no luck. VLC is always my go-to for a play anything program but it also doesn’t work, which led me to a bunch of other programs and Audacity is the only one I’ve had semi-success using the raw import.

Here is one of the files if anyone is bored and wants to take a crack at it. This is the one that I can get somewhat decent results.

I would paypal/venmo someone $10 if they can get this to a clean sounding file!

as a Raw Data import, 8bit unsigned with a 8khz sample rate is what I’ve found is ok. Using VOX encoding and 16khz sample rate is a little better. I can find variances using different encoding, etc… but it all sounds like doo doo. Again, the second file I can mess around and do the same but it is pretty terrible. I messed around with noise reduction but that seems it will ultimately lower the quality to what is possible by just finding the “right” way to import this file.

The file seems to be a “Micronas SC4 ADPCM” file. This is an ancient proprietary codec for speech recording.
I’ve not found any app that supports this format.

MPlayer was looking quite promising. It successfully detected the file type, but failed to open it.
None of my usual go-to tools were able to open it (FFmpeg, SoX, VLC, foobar2000, gstreamer).

Some of the problems:
It’s an ancient codec.
It was never a very good codec (speech quality only).
It was closed source / proprietary.
There may have been multiple incompatible versions used by different manufacturers (non-standard).
Nobody uses it these days, and haven’t for very many years.
The makers of the Rave-mp player went bust well over a decade ago.

I’m not optimistic about you finding a solution.

I found this post

It seems to be the Micronas SC4 codec. I downloaded the .acm file, installed it, and didn’t have any luck.

It came with a sample .WAV file which does appear to be similar to my file, and it opens in Audacity with the same very poor quality as my two files with custom settings in the raw data import.

I tried a couple things including downloading MPlayer, which seems to let you easily load .acm codecs, but that also didn’t work. The link above had a codecs.conf file which is similar to what Mplayer uses.

I think the only sign of hope right now is that I can’t play the sample .wav file that came with the codec, which means there is probably some way to get the codec working? Anyone know much about loading really old .acm files into some player? Being a total noob in audio related things the only next step I can think of is standing up an older system like a Win XP VM and trying there…

Here are the MPlayer failure results

C:\Users\Mitch\Downloads\mplayer-svn-38117>mplayer.exe -ao pcm MI-SC4_example.wav
MPlayer Redxii-SVN-r38117-6.2.0 (i686) (C) 2000-2018 MPlayer Team
Using FFmpeg N-92461-gd3621b2321 (2018-11-17 18:06:58 +0100)
Compiled on 2018-11-17 20:04:15 EST (rev. 1)

Playing MI-SC4_example.wav.
libavformat version 58.22.100 (internal)
Audio only file format detected.
Load subtitles in ./
Load subtitles in C:/Users/Mitch/Downloads/mplayer-svn-38117/mplayer/sub/

Opening audio decoder: [acm] Win32/ACM decoders
Loading codec DLL: ‘mi-sc4.acm’

MPlayer interrupted by signal 11 in module: init_audio_codec

  • MPlayer crashed by bad usage of CPU/FPU/RAM.

with the same very poor quality as my two files with custom settings in the raw data import.

I assume these are spoken word files? (I’m assuming that because the bitrate sort-of implies “telephone quality”.)

If it is voice and you can understand what’s being said a “typed” transcript might be your best option.