4 ms·

The Opus codec ( http://opus-codec.org/comparison/ http://opus-codec.org/comparison/ ) can enable very low latency audio. 26.5 ms algorithmic delay (the time it

by l1ambda 10y ago

The Opus codec ( http://opus-codec.org/comparison/ http://opus-codec.org/comparison/ ) can enable very low latency audio. 26.5 ms algorithmic delay (the time it takes to go through the algorithm) by default, but can be set to a very impressive 5ms. Digital audio can't achieve the near no-latency analog POTS has, but it can get pretty darn close e.g. if Opus is used in the very low latency mode. I believe Mumble and maybe TeamSpeak let you choose the Opus latency. I know some other apps like WhatsApp, Wire, and Signal use Opus as well. I don't know what settings they use though. Another problem is cell phones add ~150ms latency (pre VoLTE) and people that route calls through Google Voice adds an additional 150ms+ latency on top. If you ever talk to someone on a cell phone on google voice, it sounds like they're calling from the moon. 150ms is about the human limit before turn-taking and talking over each other becomes an annoyance. That's why cell-to-landline conversations (150ms one way) were tolerable, but cell-to-cell (300ms one way) conversations are abysmal. And that's all in the same area code. Once you add long distance, it gets worse.

doctorshady 10y ago
Just fyi, POTS is digital up until the very last mile. While the network is digital, it uses time multiplexed serial PCM streams under the hood. Aside from the delay imposed by fiber transmission at the trunk level (~40 milliseconds from one side of the US to the next. If you're using a long distance network that packetizes the connection or sends a call on some weird route, that can certainly increase), the g.711 encoding delay should be fixed at 0.125 milliseconds.
- l1ambda 10y ago
  Interesting. I didn't know g.711 was so low. Typical VOIP latency must then stem from D/A and A/D conversion and internet latency.
  - makomk 10y ago
    g.711 has such low latency because it doesn't take advantage of inter-sample redundancy in any way whatsoever - it's just raw 8-bit samples at 8 ksps with a compander on either end (traditionally on the analog side of the DAC and ADC).
77pt77 10y ago
> I know some other apps like WhatsApp, Wire, and Signal use Opus as well Opus is an evolution of SILK which is/was used in Skype.
mgamache 10y ago
I think you can get < 5ms latency with Opus depending on the sample rate.

by l1ambda 10y ago

doctorshady 10y ago

Just fyi, POTS is digital up until the very last mile. While the network is digital, it uses time multiplexed serial PCM streams under the hood. Aside from the delay imposed by fiber transmission at the trunk level (~40 milliseconds from one side of the US to the next. If you're using a long distance network that packetizes the connection or sends a call on some weird route, that can certainly increase), the g.711 encoding delay should be fixed at 0.125 milliseconds.

l1ambda 10y ago
Interesting. I didn't know g.711 was so low. Typical VOIP latency must then stem from D/A and A/D conversion and internet latency.
- makomk 10y ago
  g.711 has such low latency because it doesn't take advantage of inter-sample redundancy in any way whatsoever - it's just raw 8-bit samples at 8 ksps with a compander on either end (traditionally on the analog side of the DAC and ADC).

77pt77 10y ago

> I know some other apps like WhatsApp, Wire, and Signal use Opus as well Opus is an evolution of SILK which is/was used in Skype.

mgamache 10y ago

I think you can get < 5ms latency with Opus depending on the sample rate.