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17. IP Codec Delay: Awkward Pauses and Verbal Collisions   7/26/12 by Dave Immer

Does it seem, sometimes, that your round-trip IP signal delay is so long that, in order to avoid stepping on the far-end’s sentences, you should treat the connection like a CB radio and say “over!” when you pass the talking stick? Well, that might be a good idea when the buffer has to be large to support a stable IP connection.

Excessive delay is turning out to be a major impediment to using IP codecs for production - a problem ISDN users typically don’t have. But there are some factors we can control:
1. The quality of the internet connection:  Get the fastest service you can humanly afford! Don’t mess around here – this is the backbone of your audio bit-stream. Be willing to pay $100/month or more.
2. The algorithm: Use APT-X. This will shave 150-500 milliseconds off your round trip delay depending on what you’re presently using. I realize most people don’t have APT-X. But it is available on many platforms including Source-Connect, Musicam, APT, Mayah, Prodys, AudioTX, etc. It requires a somewhat higher bit-rate (see item 1.) The APT-X add-on costs around $500. Remember, both sides have to have it.
3. The receive buffer: Start out under 100ms and increase it if necessary.
4. Forward Error Correction: Avoid using FEC if possible, as it adds delay.

So if we are willing to throw some money at the problem to address items 1 & 2, and tweak our settings to address items 3 & 4, we should be able to minimize the delay and the resulting awkward pauses and verbal collisions. 

However, the main stumbling block to this solution is that both ends of the connection have to adopt the strategy and spend the $. It’s a ‘who-goes-first?’ dilemma and a little like herding cats to get a community of users to cooperate on such an upgrade.

Let me know if you have questions or comments about IP delay.  Thanks,