I'd approach this as follows, in real time. It assumes that the frequency
is, in average, accurate.
- Construct a 60 Hz sine- and cosine wave
- Multiply signal with either and sum up in leaky integrator (/filter)
- multiply the output of the integrater again with its sine (cosine) wave
and subtract from the input signal
The 'leaking factor' of the integrator, or filter bandwidth in general,
determines the bandwidth (tracking a jumpy guitar player needs wider BW).
BTW, using an ideal integrator this is mathematically identical to FFT-ing
the whole signal with zero padding, then zeroing out one bin, then IFFT.
Reply by Greg Berchin●April 27, 20132013-04-27
On Saturday, April 27, 2013 8:56:25 AM UTC-5, Vladimir Vassilevsky wrote:
> You mean, do the opposite of what conventional ALE does: estimate the
> stationary part and subtract it from signal ?
Yes; exactly.
> There should be optimum adaptation rate vs rejection vs artifacts.
I seem to recall in my adaptive systems class in graduate school that the two cases were presented as "equivalent" -- it was simply a matter of which you called the "desired signal" and which you called the "interfering signal".
Greg
Reply by Vladimir Vassilevsky●April 27, 20132013-04-27
Interesting.
You mean, do the opposite of what conventional ALE does: estimate the
stationary part and subtract it from signal ?
There should be optimum adaptation rate vs rejection vs artifacts. I
wonder how well it does with realistic audio.
Vladimir Vassilevsky
DSP and Mixed Signal Designs
www.abvolt.com
>On Thu, 25 Apr 2013 09:15:31 -0500, Greg Berchin
><gjberchin@chatter.net.invalid> wrote:
>
>>Adaptive line enhancer.
>
>By the way (taking this off topic), given recent Bing
>advertisements that they are the "best on the Web's most popular
>searches"; a good demonstration of the difference between Google
>and Bing can be found by searching for "adaptive line enhancer".
>On Bing, the ad that appears at the top of the list is for "Ron
>Jeremy Rates Them All - Male Enhancement Shocking Truth!". And
>Bing's RELATED SEARCHES list consists of:
> Lash Enhancers
> Bra Enhancers
> Male Enhancer
> Jewelry Enhancers
> Ring Wraps and Enhancers
> Natural Libido Enhancers
> Enhancer Definition Biology
> SmartLash Eyelash Enhancer Review
>
>Meanwhile Google just return a list of hits that are actually
>relevant (no ads), beginning with "Scholarly articles for adaptive
>line enhancer".
So you're saying an Adaptive Line Enhancer isn't going to help me be
more attractive?
Damn. That changes everything.
Eric Jacobsen
Anchor Hill Communications
http://www.anchorhill.com
Reply by jacobfenton●April 26, 20132013-04-26
>On Thu, 25 Apr 2013 09:15:31 -0500, Greg Berchin
><gjberchin@chatter.net.invalid> wrote:
>
>>Adaptive line enhancer.
>
>By the way (taking this off topic), given recent Bing
>advertisements that they are the "best on the Web's most popular
>searches"; a good demonstration of the difference between Google
>and Bing can be found by searching for "adaptive line enhancer".
>On Bing, the ad that appears at the top of the list is for "Ron
>Jeremy Rates Them All - Male Enhancement Shocking Truth!". And
>Bing's RELATED SEARCHES list consists of:
> Lash Enhancers
> Bra Enhancers
> Male Enhancer
> Jewelry Enhancers
> Ring Wraps and Enhancers
> Natural Libido Enhancers
> Enhancer Definition Biology
> SmartLash Eyelash Enhancer Review
>
>Meanwhile Google just return a list of hits that are actually
>relevant (no ads), beginning with "Scholarly articles for adaptive
>line enhancer".
>
By the way (taking this off topic), given recent Bing
advertisements that they are the "best on the Web's most popular
searches"; a good demonstration of the difference between Google
and Bing can be found by searching for "adaptive line enhancer".
On Bing, the ad that appears at the top of the list is for "Ron
Jeremy Rates Them All - Male Enhancement Shocking Truth!". And
Bing's RELATED SEARCHES list consists of:
Lash Enhancers
Bra Enhancers
Male Enhancer
Jewelry Enhancers
Ring Wraps and Enhancers
Natural Libido Enhancers
Enhancer Definition Biology
SmartLash Eyelash Enhancer Review
Meanwhile Google just return a list of hits that are actually
relevant (no ads), beginning with "Scholarly articles for adaptive
line enhancer".
Another factor to consider is how stable the mains interference signal is. In my experience it can change quite rapidly if someone is operating a dimmer, for example. If you make the notches too narrow then every time the harmonic content of the mains changes, you will hear a long "acquisition" period where the buzz is allowed through for several seconds. This is particaurly true if you are using this to remove buzz from a guitar, where the orientation of the guitar relative to the magnetic field is dynamically changing as the guitarist gyrates madly around the stage, as guitarists often do.
Bob
>Hello all,
>
>I am quite new to the world of DSP and am required to perform some DSP for
>my student job using Matlab. I need to remove the noise ofthe utility
>frequencies (60 Hz + harmonics) from a number of signals. I have been
>reading many forums on this topic and tried many possible solutions but was
>unable to get it to work properly.
>
>For instance, I tried using a notch filter and also tried a comb filter
>which worked for the first few harmonics but then started to overcompensate
>and would create spikes in the opposite direction.
>
>I also tried modifying the magnitude of the fft (I made a new variable of
>the absolute value of the fft, averaged over the whole time span
>intervals). I modified it so that the spikes at the harmonics is removed
>and interpolated a value in between them. However, all I am left now is the
>magnitude and no phase info. so I am unable to transform that into the time
>domain.
>
>Is there a standard way of filtering out these frequencies which I am not
>seeing?
>
>Please let me know.
>
>Thanks,
>Vic
Hello Vic,
I sure seems to me that there should be
a way to reduce your '60 Hz + harmonics'
to acceptable levels.
Send me your Matlab code of what you've
done so far and I'll have look. (Your FFT
scheme, as you've described it, has no
chance of doing what you want. But send me the
FFT code anyway.)
Who knows, I may be able to help.
[-Rick-]