Logitech "noise-cancelling" microphone

evandude · 04-28-2005, 07:58 PM

I'm having some issues with the logitech claim of "noise cancelling" on this microphone, which I see a lot of people like.

is there any circuitry in the microphone other than the microphone itself, and the mute switch? "noise cancelling" implies that it actively detects and cancels out noise in some manner, but without any other circuitry that is pretty much impossible... the only thing I can think of is that the lower cutoff frequency is specified at 100 Hz, which is double the 50Hz that most other similar mics specify... just blocking some low-frequency noise hardly counts as "noise-cancelling"... Although, I would imagine normal road noise would be relatively low-frequency... perhaps I will have to build an adjustable high-pass filter sometime and try it out...

Perhaps I'll get up the motivation to hook a microphone up to my oscilloscope, stick it in FFT mode, and drive around looking at the frequency spectrum to see how much low-frequency noise there really is.

Not to claim it isn't in some way better than a "standard" microphone, I just think the "noise cancelling" claim is marketing BS... ESPECIALLY if they didn't even add in any circuitry, they just chose a microphone with a larger lower cutoff frequency... So I'm curious.

What this could mean, though, is that if cutting off more low-frequency noise is the real cause for the increased sensitivity despite road noise, then anyone could potentially just add a simple resistor/capacitor high-pass filter and improve the response of their microphone in the car... a 10 cent fix for a $10 price difference between that mic and others!

0l33l · 04-28-2005, 08:02 PM

Well, who says that there is no circuitry in the MIC itself?

Let me tell you: in a quiet room, the logitech is 10043099r90q48207598e2e4 times better than my previous non-noise canceling microphone.

evandude · 04-28-2005, 08:08 PM

lol, thanks for the reply.

However, the microphone is not powered, is it? if there is no power, it is just a passive mic and all they could do is add a passive filter. That would just be reducing the sensitivity to a certain band of frequencies... such as low-frequency (50 to 100 Hz), as I had speculated. Certainly not any form of active noise cancelling... and I think that if it's just a simple passive filter, calling it "noise cancelling" is kind of BS.

But in any case, I think I will experiment. Again, it'd be nice to add 10 cents of parts to a $5 microphone and have it perform as well as, or at least closer to as well as, these $20 ones. I don't imagine it will help me very much, considering I'll probably wind up buying one of the logitech ones for testing purposes anyway... but oh well, the geek in me won't let me not at least try. I've got to do SOMETHING differently at least, since I trained SA2k5 sitting in a driveway and it understood me fine even with music playing, but as soon as I was actually driving around, it wouldn't respond to anything.

0l33l · 04-28-2005, 08:10 PM

Quote: Originally Posted by evandude

lol, thanks for the reply.

However, the microphone is not powered, is it? if there is no power, it is just a passive mic and all they could do is add a passive filter. That would just be reducing the sensitivity to a certain band of frequencies... such as low-frequency (50 to 100 Hz), as I had speculated. Certainly not any form of active noise cancelling... and I think that if it's just a simple passive filter, calling it "noise cancelling" is kind of BS.

But in any case, I think I will experiment. Again, it'd be nice to add 10 cents of parts to a $5 microphone and have it perform as well as, or at least closer to as well as, these $20 ones. I don't imagine it will help me very much, considering I'll probably wind up buying one of the logitech ones for testing purposes anyway... but oh well, the geek in me won't let me not at least try.

Look in my forum. There's the logitech MIC lookalike with the same specs for $10.

The USB version is powered. Its got analog-to-digital circuitry.

evandude · 04-28-2005, 08:36 PM

I'm going to try to figure it out. If nothing else, perhaps I can come up with an active filter that best fits the car environment and can do an even BETTER job of blocking road noise... I just have to figure out what frequency spectrum the road noise is in.

0l33l · 04-28-2005, 08:39 PM

Quote: Originally Posted by evandude

I'm going to try to figure it out. If nothing else, perhaps I can come up with an active filter that best fits the car environment and can do an even BETTER job of blocking road noise... I just have to figure out what frequency spectrum the road noise is in.

Good luck

Also block out engine noise.

Bugbyte · 04-28-2005, 08:59 PM

Here's the sum total of the analog version of the Logitech:

I think you're right about the filtering but I gotta say that it works fairly well considering how noisy the car is.

Not perfect, of course. If the windows are rolled down, forget it. But I can barely hear anything either.

electron · 04-29-2005, 08:09 AM

Here is some more info about the $10 Labtec microphone I just bought last night (The LabTec and the Logitec mentioned above are the same microphone):

http://www.cdromshop.com/cdshop/desc...855016836.html

evandude · 04-29-2005, 05:30 PM

I just went and bought these two microphones:

the logitech one was an open-box special at best buy, $16.99 so I got it even though I had JUST bought the labtec one at walmart for about $9. I'll see what I can figure out with them. Obviously i've just thrown my pipe dream of saving money by "upgrading" a cheap mic, but oh well. I'm just too curious

I did get some info from a person who's heavily into electronics and audio, and has a lot of experience with expensive noise cancelling mics, and he said that the noise-cancelling effect is actually largely due to the vents BEHIND the microphone... apparently any noise entering from the front will be picked up, but any environmental noise gets cancelled because it appears on both the front, and the vents in the back... I will have to try covering up the vents and see if it makes a difference. If that does turn out to be the case, then any of you who take your microphone apart and mount the element somewhere are essentially losing the noise-cancelling effect...

electron · 04-29-2005, 05:46 PM

Btw, for anyone wondering what is one of the best microphones out there for VR, then Acoustic Magic is the answer, but I can't imagine one of those units in a car, eventho they advertise for automotive use as well, not to mention they are VERY pricey (and yes I did own one of these for a while)

http://www.acousticmagic.com/

rando · 04-29-2005, 06:28 PM

I was just thinking about the same thing based on the picture of the guts in the other threads. I noticed the vents in front/back of these and assumed that those combined (perhaps) with the enclsoure were the 'special' noise cancelling feature.

As far as active noise canceling ... I'm not sure why you'd ever need it anyhow. Seems like the PC would be more than capable of doing this on its own.

@0l33l: You say this mic performs much better than the others in a quiet environment. How about in a noisy one like a car? In a car with the stereo blasting? With the windows down at 80mph?

Bugbyte · 04-29-2005, 06:36 PM

I can answer that. Windows down -forget it. Wind noise on the mic, at least where I've mounted it.

Stereo on, it can recognize voice commands. Stereo blasting, nope.

But I don't think that's so bad. I can't hear my passengers when the stereo's blasting. It doesn't seem like I ought to expect the computer to, either.

It would be great if there was some way to filter or process the sound to listen only to the range of your voice and then to try and filter out extraneous noises like car rumble or wind noise. I know how to do it in a post-processing environment but haven't ever heard of it being done in real time for voice.

I'll record some audio from my Logitech install while on the road and post it so you can hear the noise.

lastberserker · 04-29-2005, 06:48 PM

Quote: Originally Posted by electron

Btw, for anyone wondering what is one of the best microphones out there for VR, then Acoustic Magic is the answer, but I can't imagine one of those units in a car, eventho they advertise for automotive use as well, not to mention they are VERY pricey (and yes I did own one of these for a while)

http://www.acousticmagic.com/

No, this is exactly what you don't want in the car with a driver (obviously

) and several passangers - suddenly your carputer starts picking up random commands from their dumb chatter

Uni-directional mike sounds like a much better idea to me; given a good setup it might even solve the problem of wind noise and blasting music.

evandude · 04-29-2005, 06:55 PM

I just downloaded some noise test signals from http://www.dogstar.dantimax.dk/testwavs/

seems like i'm getting half-decent recognition with these mics, with "brown noise" in the background. However, that doesn't exactly prove anything. I never actually did "voice training" with my old mic, and I notice recognition goes up a LOT with that having been done with these mics, so I will have to do the training in the car and see how that goes

Bugbyte · 04-29-2005, 11:36 PM

I did a *lot* of voice training. By the end, I could pretty much talk at normal speed and it would recognize everything I said.