60 Hz hum causing problems with speech recognition

[Tarun Pruthi <t.pruthi@xxxxxxxx>]

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