Re: 60 Hz hum causing problems with speech recognition

[Matt Flax <flatmax@xxxxxxxx>]

On your linux problem, I recommend taking care in setting it up
properly.
It sounds like you are experiencing drop outs.
You can achieve hyper low latency using linux ... less latency then
Windows can achieve when the CPU is heavily loaded.

To do this you need to install something like ubuntustudio which is
pre-set up and compiled to run hyper low latency using linux.

The reason why patched Linux can push harder then windows is that is can
be patched with pre-emptive real time scheduling ...
 http://packages.ubuntu.com/jaunty/linux-image-rt

here is some information on setting up Jack for linux :
http://jackaudio.org/faq

Matt

On Tue, 2009-06-16 at 10:43 -0400, Tarun Pruthi wrote:
> Hi all:
> 
> 
> I have been having a lot of problems lately with 60 Hz humming noise
> in my speech recordings (I will confess that most of my tests have
> been on windows/linux laptops - and my guess is that they probably
> have much worse recording quality than desktops on average - but we
> live in a mobile world now and I have to make it work on laptops).
> Whenever it is there, it causes a serious drop in speech recognition
> accuracy, especially since it comes in very randomly at times giving
> for example clean recordings during speaker enrollment and noisy
> recordings in live testing. The problem is even worse on linux which
> has given me all kinds of artifacts in the recordings besides the 60
> Hz hum - my guess is that this is most likely because of driver
> problems.
> 
> 
> So, I have 3 questions:
> 1. What is the source of this 60 Hz noise? Powerline? RF interference?
> I have tried disconnecting the power cord - it works sometimes, but
> not always.
> 2. Is there a standard way to get rid of the 60 Hz hum and ensure
> clean recordings for the purposes of speech recognition? The only way
> I can think of is to use notch filters at 60 Hz, and some of the
> harmonics, say 120 Hz and 180 Hz, since most of the times it doesn't
> manifest as a single tone at 60 Hz, but has harmonics all over the
> frequency range.
> 3. If this is a well-known problem with sound cards, then why aren't
> we, speech recognition community, trying to come up with a mandatory
> compliance standard for sound card manufacterers which ensures that
> the microphone input is not corrupted by 60/50 Hz noise? That should
> provide a big boost to speech recognition accuracies, and a wider
> acceptance of speech recognition.
> 
> 
> Tarun
> Senior Research Engineer
> Think A Move, Ltd