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-   -   m200 voice recording differences (http://www.anythingbutipod.com/forum/showthread.php?t=64051)

greg_m 07-02-2011 05:06 PM

m200 voice recording differences
I've just started researching this recently for an oral history project. I'm looking for a very small recorder that uses primary (AA or AAA) cells rather than soldered internal battery. I would greatly appreciate any good information from the m200 community.

All these comments relate to Voice Recordings made on the m200 series.

I have an old m240 that records WAV files with ADPCM encoding, 1 channel, 4 bits/sample, 8kHz sample freq., 32kbps bitrate. (IMHO not useable audio quality.) According to Sansa CS department, all m200 series record with those same settings.

However, I recently spotted an m250 on eBay, and when the owner sent me a sample file, I found it was significantly different: IMA-ADPCM encoding, 24kHz sample freq., 97kbps bitrate! (IMHO quite useable quality for voice.)

Unfortunately, I did not win that bid, but based on that sample file, I purchased another m250. Alas, it has 8kHz sample freq., the same as my m240.

Upon further searching, I found an old thread on this board wherein the OP reported having an m250 that has a 32kHz sample freq.! Thus, it appears there may be as many as three different sampling frequencies in the m200 series. (All machines appear to produce mono WAV files encoded using 4-bit ADPCM.)

I would greatly appreciate input from anyone on this board who has an m200 series machine. Here's the data I would like to accumulate:

First, the model number and firmware version of your machine.

Second, specific information about the file:

(Move the file to your PC, right-click on the file, select Properties, then Summary, then Advanced if necessary. Then please post the following:

1.) Bitrate
2.) Audio sample size
3.) Channels
4.) Audio sample rate
5.) Audio format.

A posted audio sample file would be wonderful, but isn't absolutely necessary.

Thanks in advance to anyone who takes the time to participate in this research project!

skip252 07-02-2011 05:36 PM

Results from my old m230

1.) Bitrate-32.8 Kbps
2.) Audio sample size-(file size?)-26.1 KiB
3.) Channels-1
4.) Audio sample rate-8 000 Hz
5.) Audio format-ADPCM

Sansa m230
Firmware version-3.2.8A

I suspect, although I have no way to confirm this, the information from Sandisk CS is inaccurate. There is a version of the m200 series that is different from the others. It has a different chipset. Since the performance would be the same Sandisk CS would probably have the same information for all models regardless of the actual internal hardware..

You can find more information about what's called the M200v4 on the Rockbox M200V4 port page. Rockbox developers need to know exactly what hardware is in each player in order to reverse engineer a replacement firmware. The first part of that its to tear down the player and accurately identify the hardware. You may find the information you need there.

greg_m 07-02-2011 09:32 PM

Skip, thank you very much for checking and posting that info!

When I use XP's File Properties menu, I find that "Audio sample size" is reported as 4 bits. That makes sense: 8,000 samples/second x 4 bits/sample = 32kbits/second.

I started to look at the Rockbox forums, but there are over 100 pages, covering several different Sansa models, and it's much too deep for me to digest.

I suppose one could look up the chipset for the V1/2/3 players, and see what encoding formats they're capable of. Perhaps they are capable only of (8kHz x 4 bits). But, if they're capable of better quality, then the spectre of changing a few bytes in the firmware rears its ugly head... with the possibility of bricking.

At any rate, I hope that some more members will post data here. I especially want to find out which versions record at a higher quality level... if there is some clear pattern.

Thanks again!

ted209 08-17-2011 03:21 PM

I still love this player, and have started using it again in my car. Here's my details:

m260 (blue) firmware: 2.2.5A

from a recorded wav file:
1.) Bitrate: 32kbps
2.) Audio sample size: 4bit
3.) Channels: 1
4.) Audio sample rate: 8 kHz
5.) Audio format: Microsoft ADPCM

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