Subject: Re: 60 Hz hum causing problems with speech recognition From: David Mountain <dcm@xxxxxxxx> Date: Tue, 16 Jun 2009 11:25:46 -0400 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>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. -------------------------------------------------------------------- David C. Mountain, Ph.D. Professor of Biomedical Engineering Boston University 44 Cummington St. Boston, MA 02215 Email: dcm@xxxxxxxx Website: http://www.bu.edu/dbin/bme/faculty/?prof=dcm Phone: (617) 353-4343 FAX: (617) 353-6766 Office: ERB 413 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 >