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Re: 60 Hz hum causing problems with speech recognition

I'd like to vote for this concept ... except slightly modified.

You can check that you can get rid of the hum by running your laptop off
its battery without the power adapter.

Remove all mains power. Use a car battery (possibly deep cycle if you
plan to run for more then a day at a time).

This is how I run my studio ...

don't use an inverter to get mains power back, use a DC to DC
converter ... like this one to step up for a laptop :

If you need to power the usb audio card with DC, then convert to that
using this step down converter :

You will now have no hum...

You will have to purchase a car battery charger and use it to charge the
battery over night or when your recording is not in progress.


On Tue, 2009-06-16 at 20:11 +0100, Peter Lennox wrote:
> is it possible to eradicate the hum entirely by only using non-mains items? - try this - a car battery and an inverter to power the mains-only items - still there? - or simply, a dynamic mic and the laptop on battery - any good? - it does sound like mains hum to me, and this is down to the power supply. In the old days, when using a mac over a 10Kw PA - it was absolutely vital to make sure the mac had a decent battery - no mains adapter acceptable. Hifi buffs use car batteries to push their stereo because of dirty mains.
> regards
> ppl
> Dr Peter Lennox
> Director of Signal Processing and Applications Research Group (SPARG)
> School of Technology,
> Faculty of Arts, design and Technology
> University of Derby, UK
> e: p.lennox@xxxxxxxxxxx
> t: 01332 593155
> w: http://sparg.derby.ac.uk/SPARG/Staff_PLX.asp
> ________________________________________
> From: AUDITORY - Research in Auditory Perception [AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Piotr Majdak [piotr@xxxxxxxxxx]
> Sent: 16 June 2009 19:38
> To: AUDITORY@xxxxxxxxxxxxxxx
> Subject: Re: 60 Hz hum causing problems with speech recognition
> In Europe, we call it "the 50-Hz hum" :-)
> Tarun, I also vote for a ground loop. You could look if you have more
> than one device grounded. If you have no grounded devices try to ground
> the mic-preamp. Usually this helps in our lab.
> Good luck,
> Piotr
> Pierre Divenyi wrote:
> > Tarun, you have two options: (1) get rid of the ground loop that is
> > quite probably the culprit, or (2) move to Europe where the 60-Hz hum
> > is unknown.
> >
> > -Pierre
> >
> >
> > On 6/16/09 7:43 AM, "Tarun Pruthi" <t.pruthi@xxxxxxxx> 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
> >
> >
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