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This is my first time posting here and also my first time attempting to do reverse engineering of this kind.

Let´s get to the point: I have to find a way of reading some phone call audio files. The files have a mysterious ".vx8" extension which yields no relevant results on google. The format seems to be proprietary from the software.

On other questions here, I saw that trying to open the file in VLC and looking for metadata (Ctrl+I) is usefull. This yields no information on VLC other than the filename.

I do not have access to the software that makes these files (which is key part of some suggestions found here as well)

Here is the head of the hexdump for some files.

hexdump -C 01Z7I579.vx8|head
00000000  01 e1 70 fc e1 ee 64 d6  01 80 80 08 80 08 08 08  |..p...d.........|
00000010  09 00 08 08 08 80 08 08  08 80 80 80 09 00 80 08  |................|
00000020  80 08 80 80 80 80 08 80  08 80 08 80 08 09 18 80  |................|
00000030  08 80 08 08 08 08 08 08  08 80 80 08 08 80 80 80  |................|
00000040  08 08 08 08 08 08 80 08  80 80 80 08 08 08 80 09  |................|
00000050  18 08 80 80 80 09 18 80  80 08 80 08 08 80 81 90  |................|
00000060  80 08 08 81 90 88 18 80  08 08 08 80 08 80 00 90  |................|
00000070  08 08 08 80 09 18 80 08  80 08 80 08 80 08 80 00  |................|
00000080  90 08 80 80 08 80 08 80  09 18 09 18 80 09 01 89  |................|
00000090  00 08 80 08 80 80 00 98  10 90 08 80 88 18 80 08  |................|

hexdump -C 01Z7I5EZ.vx8|head
00000000  01 d1 55 86 7c f0 64 d6  01 08 08 08 80 08 08 08  |..U.|.d.........|
00000010  80 08 08 08 08 08 08 08  08 08 08 08 08 08 08 08  |................|
00000020  08 08 08 08 08 08 08 08  08 08 08 08 08 08 08 08  |................|
00000030  08 08 80 08 08 08 08 08  08 08 08 08 08 08 08 08  |................|
00000040  08 08 80 08 08 08 08 08  08 08 80 08 08 80 08 08  |................|
00000050  08 08 08 08 08 08 08 08  08 08 08 08 08 08 08 08  |................|
*
00000070  08 08 08 08 08 08 08 08  08 08 08 08 80 80 80 08  |................|
00000080  08 08 08 08 08 08 08 08  08 08 08 08 80 08 08 08  |................|
00000090  08 08 08 08 08 08 08 08  08 08 08 08 08 08 80 08  |................|

hexdump -C 01Z7I5IZ.vx8|head
00000000  01 16 62 09 54 f1 64 d6  01 fd 14 8a 82 10 a8 a2  |..b.T.d.........|
00000010  0c 23 42 83 e8 99 0b 88  38 a3 22 b1 0f 08 11 12  |.#B.....8.".....|
00000020  ad 02 0f 94 88 09 03 00  a2 49 0c b3 6b c2 1d 11  |.........I..k...|
00000030  b9 34 0b 30 32 ca 90 49  90 b0 01 b0 08 13 9f 08  |.4.02..I........|
00000040  88 a1 51 12 8b a2 4d 01  92 af 82 4c 80 80 18 a0  |..Q...M....L....|
00000050  34 10 a3 28 f8 18 80 0b  c8 81 9a 60 28 9b 09 00  |4..(.......`(...|
00000060  b7 21 9b 3c 81 92 4b ac  52 ab 52 9a 0b a3 0e 85  |.!.<..K.R.R.....|
00000070  29 92 b8 23 a0 2a db 39  98 20 2c e2 29 b9 62 1b  |)..#.*.9. ,.).b.|
00000080  85 3b c3 48 a9 d8 90 1c  54 09 c1 09 a1 20 38 e8  |.;.H....T.... 8.|
00000090  2a 99 31 00 1a ab b2 52  a3 73 bf 02 bb 33 1d 12  |*.1....R.s...3..|

hexdump -C 01Z7I589.vx8|head
00000000  01 96 1c 87 09 ef 64 d6  01 20 39 35 3a 21 1a 8b  |......d.. 95:!..|
00000010  10 cb 32 b2 33 22 dc 91  f9 92 80 a4 01 a3 03 b3  |..2.3"..........|
00000020  37 01 14 1b 81 28 a1 6a  a1 3a af bb ff 9a a9 40  |7....(.j.:.....@|
00000030  20 24 49 02 0a 98 80 b9  23 b2 44 00 9a f0 b9 c2  | $I.....#.D.....|
00000040  81 a3 04 a2 11 83 33 20  25 28 18 39 2a 69 08 1b  |......3 %(.9*i..|
00000050  2e cb ef c1 ba 13 03 85  31 93 09 b0 81 bb 34 99  |........1.....4.|
00000060  52 29 11 bb bf f0 9a 04  00 82 30 c2 39 92 42 09  |R)........0.9.B.|
00000070  31 bc 41 0a 51 99 11 cf  9b ff 1a 90 20 18 42 19  |1.A.Q....... .B.|
00000080  21 9a 00 0a a3 2a 97 11  a2 1b e1 e8 09 93 90 10  |!....*..........|
00000090  03 91 48 03 31 58 31 08  29 12 19 8b 10 8d da df  |..H.1X1.).......|

As you can see, for some of the files, 8´s and 0´s are abundant (I have no clue why) and some other don´t have them at all.

The 8th and 9th bytes are always d6 01

The audio samples seem to begin on the 10th byte.

I have requested to the person with access to the files and software to send me some pairs of files for the same audio (.mp3 and .vx8) to try to see the difference in size and infer some bitrate (As suggested in other questions). They have sent me mp3 files before (not for the same phone calls) and the mp3 files seem to be larger than the .vx8, but I will have to confirm this once I have the pairs.

It would be very helpful to know any other strategies that I might be missing.

Thank you

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1 Answer 1

Reset to default
2

It's look like data from a wav file

Try to use free software Audacity
File -> Import -> Raw Data... Encoding : 16bit pcm, or 8bit or ... Byte order Little Endian , Channels : 1 Mono, Start offset : 0 bytes , Amount to import : 100% Sample rate 16000 Hz. or 8000 or ...

if it doesn't work it would be interesting to have the name of the software that produces these vx8 files and if possible a complete file

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1
  • Thanks for your help! I tried importing with the initial settings you mentioned and the audio would play mostly loud noise but in the back I could hear the voices softly (after adjusting the sample rate a little). So I started to try all the import combinations and the last option "VOX ADPCM" (8000 Hz) seems to do the trick! However the audio wave does not seem to be centered at 0 (in fact the center moves around as the audio goes on) I don´t know if this is a problem or not (the speech is very understandable)
    – Manuel Ruiz
    Commented Aug 17, 2020 at 15:02

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