pop and jitter at the start of transmissions from DMR

Patrick Perdue


This is nothing new, but I'm trying to figure out where it's coming from.

At the start of each DMR transmission, when listening on Allstar, there is a small pop sound. I've been on some other Allstar nodes that appear to be using a similar configuration, though I don't know for sure, which don't exhibit this behavior. This occurs regardless of whether or not I am using hardware or software AMBE vocoding.

Perhaps related, but maybe not, lately, at the start of DMR transmissions, there is sometimes severe jitter for about the first second of audio, then everything is fine for the rest of the transmission. This is a problem if someone quickly keys to give a callsign, then unkeys again. Perfectly understandable with a DMR radio, but these very short transmissions end up completely broken on the other side of Analog_Bridge.

This could very well be attributed to the Brandmeister server I'm using. I'll investigate this some more. It may even be an ASL issue. This bridge is off-site, connecting to a larger Allstar node on a VPS, but directly connecting to the private node hosting the bridge through iaxrpt suggests that the connection to my larger node is not the problem.

I'm using the latest versions of MMDVM_Bridge and Analog_Bridge from Github as of this writing. Analog_Bridge.ini is all defaults, with the exception of txTg and AGC setting ,which are not relevant to this set of problems as far as I can tell.

Raspberry Pi 2 running ASL and DVSwitch, ThumbDV via AMBEserver. I also tried using a direct serial connection to the dongle from A_B, which worked about the same as using AMBEserver as far as I could tell. I have also tried playing with the jitter parameter of MMDVM_Bridge, but ended up setting it back to 360.