Tips for mastering for GSM 6.10

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Tips for mastering for GSM 6.10

Postby DwaneHollands » Tue Dec 17, 2013 6:53 pm

Hi guys,

I have a VOIP phone system that I want to create some on hold music and welcome messages.

It requires a very specific WAV file with the GSM 6.10 codec. (8000hz in mono among other things)

It is a shocking codec. I mean it adds it's own noise in a seriously bad way. (8000hz in mono as a standard WAV file is practically HD in comparison. It's the codec that is the culprit. Sounds like bad reception or driving through a tunnel and that's when I play it back on the PC before I put it on the phone system.)

Has anyone else had the misfortune to try and master for this codec with good results? I'm. Thinking there's some threshold I have to get over in order to get the most out of the codec. Maybe slamming it super loud. I dunno.

There are no other formats it will accept and no other phone systems that we can use. We're stuck with trying to get the most out of it.
Dwane Hollands

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Re: Tips for mastering for GSM 6.10

Postby Kurt » Tue Dec 17, 2013 11:18 pm

Wow, it really does sound shit doesn't it!

The old POTS telephone network had a very narrow bandwidth, about 400hz to 3400hz. Mobiles might be better but I doubt it. The codec seems to cope better if you high and low pass the signal before resampling and then compressing.
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Re: Tips for mastering for GSM 6.10

Postby DwaneHollands » Wed Dec 18, 2013 8:47 am

Hey that's a good idea Kurt! I'll give that a go! Cheers!
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Re: Tips for mastering for GSM 6.10

Postby DwaneHollands » Wed Dec 18, 2013 10:02 am

There's actually another format that it allows! It also allows a WAV file that uses PCM codec. I misunderstood the specs. (my bad)

I mean 8khz in mono is no picnic, but there's no noise anymore! Which is a huge leap forward in quality!

Now, there's very little top end, so I'll have to try and clean it up as best I can to get a less muddy result.

but it's happy days! lol.

EDITS: forgot tips...

P.S. A tip for anyone who has to do this. Download Audacity for the conversion. It has the codecs for GSM 6.10 if you must use it, but also the particular format of WAV (Microsoft) Signed 16 bit PCM. (The wav file with PCM, straight out of Reaper won't work). The audacity version for Mac and PC both work.

This is for a Yeastar myPBX system. I'm not sure what other systems use, but if you come across the issue, hopefully this information will help, because I couldn't find much on google.

Another Tip for both codecs. When you export from your DAW the master file, that you will convert to the shabby codecs. Save as Mono from there. Then open in Audacity. Then Change the Project Rate (Hz) to 8000, then Export to the codec you want. Otherwise when you try and import it into the myPBX system, it will not play back.
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