Re: 60 Hz hum causing problems with speech recognition

[David Mountain <dcm@xxxxxx>]

I've seen problems with both 60 Hz interference and more commonly with
digital noise from the laptop hardware.  If you use a USB microphone, you
can avoid these problems.  To clean up existing recordings with 60 Hz
interference, you can use a FFT based filter to high-pass filter with the
cutoff set a little bit above 60 Hz.

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David C. Mountain, Ph.D.
Professor of Biomedical Engineering

Boston University
44 Cummington St.
Boston, MA 02215

Email:   dcm@xxxxxx
Website: http://www.bu.edu/dbin/bme/faculty/?prof=dcm
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On Tue, 16 Jun 2009, 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
>