Voice Latency Test Results

[AzzAz]

I tested Google Voice latency to POTS (plain old telephone system a.k.a. landline), GSM (Net 10 which uses AT&T's network), CDMA (Sprint) and a VoIP provider, because I couldn't find much information other than conjecture about actual voice latency on these systems.

I used Audacity to do the tests, it's really easy to do if you have a mic and speakers. (I'd be interested to hear what others measure. Be sure to calibrate audacity so you don't include the latency of your sound card in the measurements.)

These tests measure the time it takes, for sound to enter one device and come out the other device. In other words, the one-way time it takes for your speech to reach your calling party (and vice versa). They say that just 40 or 50ms of latency is the point at which voice delay becomes noticeable.

Here are the results!

land line to Sprint: 149ms
land line to ATT: 162ms
sprint to ATT: 291ms
landline to Google Voice to Sprint: 279ms
landline to VOIP: 326ms
Sprint to VOIP: 450ms
VOIP to GV to Sprint: 750ms

From these, I estimate POTS has a latency around just 10ms...extremely good, and as to be expected. Once you get on a cell-to-cell call, you have almost 300ms latency. At this point conversation starts to becomes more half-duplex than full-duplex; that is, talking over one another and waiting to speak, similar to a walkie-talkie.

Google Voice seems to be like a cell phone in terms of latency, so calling Landline -> GV -> Cell is similar to a cell-to-cell call. Cell to GV to cell should be something like 430ms (quite a bit of delay).

CDMA appears to be slightly better than GSM, but not really significantly different.

VoIP is pretty bad, twice as worse than a cell phone, and I notice this subjectively as well. I really tried hard to get the lowest lag on VoIP too, by using 0.010 ms packet size and lowest possible jitter buffer. Ping command indicated less than 40ms (round trip time) to the VoIP servers. The VoIP delay could also be due to the long-distance transit time as the datacenter is in Texas.

Google Voice is great but the added latency for phone calls is to me, a deal killer.


Links: Why is there a huge delay on my phone calls? http://www.google.com/support/forum/...08334667&hl=en

[RHDScrambler]

There's definitely some minor lag when using it with VOIP. But the advantage of unlimited free calls is worth it for me. What VOIP provider are you using? I first tried GV with Magicjack, definitely a bad combo. Horrible lag and connectivity issues. With Gizmo5 though, the lag is barely noticeable.

[AzzAz]

VoIP was with link2voip.com. Ping time to rtp.us2.link2voip.com of ~40ms.

I would be happy to test with another SIP provider if someone wants to lend me an account.

I'm also curious about ooma and Skype.

[AzzAz]

By the way, a Cell-to-Cell call over Google Voice is what I suspect most people are making.

I estimate that to have a one-way latency of about 430ms according to my calculations. That's nearly half a second and explains the complaints people are having.

[larrycl]

Thanks for these tests!

These seem to confirm what I've notices qualitatively, which is that Google voice adds significant latency and in certain cases renders it nearly unusable.

I've tried forwarding my google voice to:
a) my cell phone
b) my DID that then forwards to my SIPGATE Voip line (also tried with my IPKall DID)
c) my Gizmo VOIP line

I've found both (a) and (c) are usable, but there is definitely some latency. However, (b) adds so much latency that it is nearly impossible to have a full duplex conversation. The latency is very bad and noticed by all parties. In fact I heard comments from people asking why I was pausing so much.

[beaucoup]

Google Voice doesn't "add" anything. The latency and connection you have is dependent on many factors. I use GV with Gizmo and the calls are just like any other call, with no latency or lag at all. I've done it with SIPDroid and the call is fine but there is a definite lag.

Obviously the data connection for cell phones need to improve for true VOIP calling.

[AzzAz]

Google Voice doesn't "add" anything. I use GV with Gizmo and the calls are just like any other call, with no latency or lag at all.

Then post your scientific measurements like I did. Just because you don't notice it doesn't mean it's not there. According to my tests, GV adds about 130ms of lag.

Other lag reports:

http://www.google.com/support/forum/...08334667&hl=en

http://www.google.com/support/forum/...2984630a&hl=en



By the way, All my numbers I posted have been one-way. That means you should double them to get a true "ping" time. This would represent the absolute minimum time between when you finish speaking and when you could start hearing your calling party's response.

[briareus]

Google Voice does 3 things, SMS, Voicemail, and phone calls. The other features are superb. But in my opinion, the added latency for phone calls is not worth it. Calls are delayed enough with cell phones; it doesn't make sense to add more frustration when making phone calls even for the convenience of a single number.

I rarely notice it. GV's features are completely worth it IMO but, obviously, YMMV.

[beaucoup]

Then post your scientific measurements like I did. Just because you don't notice it doesn't mean it's not there. According to my tests, GV adds about 130ms of lag.

Other lag reports:

http://www.google.com/support/forum/...08334667&hl=en

http://www.google.com/support/forum/...2984630a&hl=en



By the way, All my numbers I posted have been one-way. That means you should double them to get a true "ping" time. This would represent the absolute minimum time between when you finish speaking and when you could start hearing your calling party's response.

I'm not disagreeing with you, GV may very well add a delay, as noted by your own experiences.

But you do understand that everyone is going to have different experience based on MANY different factors. The data connection someone has on their PC, the data connection on the cell, the speed of the phone or PC. If someone is using it in a house where the connection is split with 6 people.. if someone's using dial up in the boonies somewhere in the California desert, it's going to have an effect.

There are so many factors, that a blanket "GV adds 130ms to all calls" statement is just too broad to prove. I, for one, have no issues with any delays, so I'm just saying everyone's experience will be different.

[AzzAz]

Prove me wrong then. Post your numbers.

Are you in California? Could be no delay there if the Google Voice data centers are there.

I find the people that "don't notice it" generally just don't talk on the phone a lot or they don't participate in conference calls. If you pretty much only make cell-to-cell calls, then you probably fall into this category, since cell calls have 600ms round-trip delay.

[balazer]

Echoing beaucoup's comments, I use Google Voice with Gizmo5, and I've never noticed the delay. I'm not a big talker, but I do at least one conference call everyday.

Delay measurements are nice, but I'm not going to bother with that. Simply, if the delay is not a problem for you, it's not a problem. If it is, it is.

[AzzAz]

Right, but the whole point of this thread is to post real, hard numbers. I agree that if the delay is not a problem for you, it's not a problem for you. However, those kinds of posts are a dime a dozen and really do not add any meaningful information. They come across like "well it works for me! therefore, nobody else could have any legitimate issues with it!"

[balazer]

If you want to just talk numbers, then stick to the numbers. You said "But in my opinion, the added latency for phone calls is not worth it." I thought a differing opinion was warranted.

[AzzAz]

If you want to just talk numbers, then stick to the numbers. You said "But in my opinion, the added latency for phone calls is not worth it." I thought a differing opinion was warranted.

Ah, you're right. fair enough

[mikethaler]

How does one measure latency? I know how to do it on a computer (ping).

...mike