Codec 12 - IMA ADPCM 8 KHz

[wa6hzt]

I am moving to a 3G connection where I will have to count every kB and need to run codec 12, IMA ADPCM 8 khz.

I have been running it for a few days and have noticed it begins to distort quite a bit after some period of time. I can clean it up by powering off the local controller, but not by restarting it. I am running software 2.57 and an Icom-706MKIIG. Codec 0 is solid as a rock, but, now, with limited bandwidth, I need Codec 12.

I haven't figured out what triggers it into distortion (very difficult to explain, almost like harmonic bursts on voice peaks with low frequency components), nor does it start at a regular interval. But, when it works, it is perfect,

Has anyone else encountered this behavior? Anything I can do at this end to help isolate the cause?

Many thanks and 73,

Gary

[OH1MTS]

I'm running 3g also and have problems that just ramdomly red led turns on and I need to reconnect (mode 0 in both ends). I tested mode 12 in radio and mode 2 in control and noticed that connection stays on better but the same distortion behavior as you wrote and I also need to disconnect power from control.

My connection averages downlink 5Mb uplink 3mb latecy 45-60ms.

[sm2o]

RED LED means that no RTP packages (audio) are comming in at all. I doesn't matter which codec you use. With the IMA ADPCM  there is a risk of distortion if a package is lost and the decoding goes out of sync. We will look if it's possible to resync periodically.

/mike

[wa6hzt]

Thank you! That would explain the random nature of the problem. Yes, please, if there is anything you can do to be proactive to help the codec "right" itself again it starts distorting, it would be greatly appreciated.

Are there any settings I can optimize to guard against this, that would not eat more bandwidth?

73

[sm2o]

Hi

Have tried for several day to disturb the itnernet connection with our "bad Internet simulator" but we can not find away to get them in to the distorted situation.  Even if the offset are wrong some times beacuse of lost packages it's only for a short moment before it is fixed automatically.
Can any of you which have det IMA ADPCM problem make a recording that we can get an analyze ?

73 de mike