Software Based Echo Cancellation?

tcyun asks: "I am helping to put together a small studio for a project at my workplace which will require some audio mixing. We have been able to find software solutions (often times open source) for almost all of our needs except for echo cancellation. I have done the requisite searches and have found a large number of hardware based echo cancellation devices, but have not found a purely software based solution. Is anybody aware of one?"

"For some more information, my office is trying to get a small system up and running that will allow multiple locations to video conference together. We have some specific requirements and have a fairly good handle on the entire video part of the problem.

However, we are running into problems with parts of our audio mix. The first issue is something that (I believe) is called 'mix minus.' This means that in a group conference, speakers do not have audio sent back to their location. (This is important for various psychology and network latency related issues.) There are several hardware based solutions that are available and we have some software based options.

The larger problem is echo cancellation. As many people may need to speak at once (and to avoid the requirement of having individuals constantly muting their microphones), we would like an echo cancellation component. The ideal would be a software solution that we could run locally, perhaps in conjunction with the same code running on the remote systems. However, most of the solutions we have found are hardware based (DSPs, ASICs, etc.).

The technology used on the studio side as well as the host side will involve various operating systems. We are trying to avoid avoid relying on specific OTC hardware solutions (namely, sound cards) as we would like to be able to create a solution that would function over time, particularly as specific hardware solutions tend quickly to horizon. So, having nice code that could be compiled on different systems would be a plus. Ideally, we would like to minimize the amount of hardware necessary, so an echo cancellation algorithm that could run in conjunction with other processes would be nice, but it is not a requirement."

Comments

how do you do that?

[vladkrupin]

wouldn't the echo cancellation itself propogate over time and create artifacts in the sound? Or am I totally misunderstanding the issue altogether?

we need more

[RealisticWeb.com]

This is a great question you are asking, and I would love to see a good answer. The shame of it is, I'm expecting to see a bunch of posts in response to this saying "If you need one then write it yourself".

Is it just me, or does it seem like the open source offerings for things related to audio/video are lacking in general? I wish I had time to make improvements myself, or the money to contribute to the developers, but it seems like we need more in this area to be able to be more competitive with proprietary solutions.

Re:Hack old Modem Drivers!

[mellifluous]

I don't think this is quite the same problem. Ring cancellation is looking for a very particular sound with known characteristics. Echo cancelation has to supress the delayed versions of an aribitrary sound feeding back through the system.

perhaps the reason you can't find it...

[ultramk]

...is because it doesn't exist.

Realtime processing, AFAIK, be it audio or video, is astonishingly processer-intensive. It doesn't surprise me that DSPs are being used for this reason: they may be the only thing that can cut it in a cost-effective manner.

i.e. you may be able to build a high-end workstation, and write some real-time software to handle this task, but since it probably wouldn't be able to do anything else at the same time doesn't that qualify as a hardware solution?

Perhaps instead of going to extreme lengths to remove echos, perhaps you just need to work harder to prevent them in the first place? Pro audio mags have tons of ways to reduce echo and other unwanted effects in small (usually home) studios. Have you looked into this?

Michael-