What kind of audio file?
Find out the magic numbers for your file format which identify the file (in the same way that say GIF files always have "GIF" as the first 3 characters).
Is your Mac running OS X ?
Do you have command line tools like 'dd' and 'hd'?
1. Plug the thumb drive in and find out what device it becomes.
Code:
$ dmesg | tail
[ 793.755691] usbcore: registered new interface driver uas
[ 794.787229] scsi 6:0:0:0: Direct-Access USB DISK 2.0 PMAP PQ: 0 ANSI: 0 CCS
[ 794.787847] sd 6:0:0:0: Attached scsi generic sg2 type 0
[ 795.835943] sd 6:0:0:0: [sdb] 4055040 512-byte logical blocks: (2.08 GB/1.93 GiB)
[ 795.836560] sd 6:0:0:0: [sdb] Write Protect is off
[ 795.836563] sd 6:0:0:0: [sdb] Mode Sense: 23 00 00 00
[ 795.837182] sd 6:0:0:0: [sdb] No Caching mode page found
[ 795.837185] sd 6:0:0:0: [sdb] Assuming drive cache: write through
[ 795.864366] sdb:
[ 795.867318] sd 6:0:0:0: [sdb] Attached SCSI removable disk
2. As 'su', start dumping from the start of the media
Code:
$ sudo dd if=/dev/sdb | hd | less
00000000 eb 3e 90 2a 35 3e 2b 6b 49 48 43 00 02 40 20 00 |.>.*5>+kIHC..@ .|
00000010 02 00 02 00 00 f8 00 01 20 00 10 00 00 00 00 00 |........ .......|
00000020 00 e0 3d 00 00 01 29 29 33 08 ae 20 20 20 20 20 |..=...))3.. |
00000030 20 20 20 20 20 20 46 41 54 31 36 20 20 20 f1 7d | FAT16 .}|
>> more and more and more
If your paging tool (less) has search features, then search for the magic numbers of the file format.
Once located, make a note of the hex address at the start of the line. Make sure it is sector aligned (xxxxx[02468ace]00) because it should be at the beginning of a file. You have to convert to decimal and divide by 512 (to arrive at a value of nnnn) for the next dd step.
3. Copy the raw sectors
Code:
$ sudo dd if=/dev/sdb of=recovery.bin skip=nnnn count=xyz
If you have a rough idea how large the file might be, then xyz is how many sectors. Or you can omit count and it will copy the remainder of the thumb drive to the recovery file.
I would suggest you get a second thumb drive and record a single short recording to it, then practice with the above steps so you're sure of what you're looking for.
WARNING:
Make absolutely sure your if and of parameters are what you want.
It is so very easy to trash your OS if you get it wrong - check and check again before pressing enter!
You might be able to use this instead.
PhotoRec - Wikipedia