Apparently there is a relationship between muscle fatigue and the frequency of the EMG signal.
http://www.ncbi.nlm.nih.gov/m/pubmed/8785930/
So this might be why you would want to track the frequency.
Bob
Reply by ●March 6, 20142014-03-06
On Tuesday, January 24, 2012 11:21:59 PM UTC+8, marieclare wrote:
> I am using MATLAB to analyse EMG signals. So far I have rectified the data
>
> and performed a STFT (using a Hamming Window). I am now looking to
>
> calculate the median frequency of the power spectrum and would be grateful
>
> if someone could advise me on the best way to do this.
>
>
>
> Thanks
Hi, I am also using STFT to analyse my EMG data. Any guidelines for me to do on STFT? thank you :)
Reply by maury●January 28, 20122012-01-28
On Jan 27, 4:57�pm, Mac Decman <dearman.m...@gmail.com> wrote:
> On Fri, 27 Jan 2012 10:41:09 -0500, Jerry Avins <j...@ieee.org> wrote:
> >On 1/27/2012 7:06 AM, Mac Decman wrote:
>
> > � ...
>
> >> I don't think the OP is dealing with spectrums as much as he is
> >> dealing with IF of the signals. �Not sure but from what I have read on
> >> the subject I believe this. �I would be happy to hear the reply from
> >> the OP.
>
> >I meant to ask before. It can't be "intermediate frequency". What does
> >IF mean here?
>
> >Jerry
>
> Instantaneous Frequency. �Sorry I forget how many people are in
> communications. There's a little acronym overlap. �I'm pretty sure
> that is what the OP really wants since he mentioned STFT.
>
> Mark DeArman
Thinking out loud here. Take the FFT of the EMG signal. Once he gets
the FFT, if he integrates the FFT, then he could get a spectrum
envelope. Then take the final value and divide by 2. This would give
the "half-spectrum energy" value. Find the frequency that corresponds
to this "half-spectrum energy" value, and that would be the median
frequency he's looking for.
Maurice Givens
Reply by Mac Decman●January 27, 20122012-01-27
On Fri, 27 Jan 2012 10:41:09 -0500, Jerry Avins <jya@ieee.org> wrote:
>On 1/27/2012 7:06 AM, Mac Decman wrote:
>
> ...
>
>> I don't think the OP is dealing with spectrums as much as he is
>> dealing with IF of the signals. Not sure but from what I have read on
>> the subject I believe this. I would be happy to hear the reply from
>> the OP.
>
>I meant to ask before. It can't be "intermediate frequency". What does
>IF mean here?
>
>Jerry
Instantaneous Frequency. Sorry I forget how many people are in
communications. There's a little acronym overlap. I'm pretty sure
that is what the OP really wants since he mentioned STFT.
Mark DeArman
Reply by maury●January 27, 20122012-01-27
On Jan 27, 9:38�am, Jerry Avins <j...@ieee.org> wrote:
> On 1/27/2012 6:47 AM, Rick Lyons wrote:
>
>
>
>
>
> > On Fri, 27 Jan 2012 03:50:08 -0500, robert bristow-johnson
> > <r...@audioimagination.com> �wrote:
>
> >> On 1/26/12 9:58 PM, Rick Lyons wrote:
> >>> On Tue, 24 Jan 2012 09:21:59 -0600, "marieclare"
> >>> <marieclare.mccormick@n_o_s_p_a_m.uws.ac.uk> � wrote:
>
> >>>> I am using MATLAB to analyse EMG signals. �So far I have rectified the data
> >>>> and performed a STFT (using a Hamming Window). �I am now looking to
> >>>> calculate the median frequency of the power spectrum and would be grateful
> >>>> if someone could advise me on the best way to do this.
>
> >>>> Thanks
>
> >>> Hello marieclare,
> >>> � � If you have signal, let's call it signal "A".
> >>> If you rectify signal "A" you have a different signal
> >>> that we'll call signal "B". � I hope you
> >>> realize that the spectrum of signal "A" will not
> >>> be the same as the spectrum of signal "B".
>
> >> oh c'mon Rick, you're not saying that two signals need be at all alike
> >> to have the same spectrum. �say A is a dirac impulse and B is white
> >> noise. �two impossible signals with real-world approximations that have
> >> nothing to do with each other except, um, i forgot.
>
> > Hi Robert,
> > � �no, I sure didn't mean to imply that two signals need
> > be at all alike to have the same spectrum. �Perhaps
> > I misunderstood the original poster. �It just seemed odd
> > to me that he said he's analyzing an EMG signal and I
> > assumed by "analyzing" he meant spectrum analysis.
> > And then he said he was rectifying the EMG signal, and
> > that would produce a signal with a different spectrum
> > than the spectrum of the original EMG signal. �I was merely
> > trying to point that out to the original poster.
>
> > Being that I know nothing about analyzing EMG signals,
> > perhaps I should just keep quiet.
>
> I don't know how modern analyses of EMGs are done, but I suspect that
> the term "rectify" here isn't related to absolute values, but maybe to
> taking the tilt out of the baseline. I've heard it used that way in
> Auger spectrometry.
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
> �����������������������������������������������������������������������- Hide quoted text -
>
> - Show quoted text -
Hi Jerry,
I know very little about this (my research advisor was into bio-
medical stuff), but from what I understand, EMG is the
electromyographic signal produced by a muscle. The signal is indeed
rectified. The sequence, as I understand, is to rectify (absolute
value), low-pass filter to get the envelope, and then integrate the
filtered signal to determine the level of muscle activity.
That's all my knowledge on the subject :>)
Maurice
Reply by Jerry Avins●January 27, 20122012-01-27
On 1/27/2012 7:06 AM, Mac Decman wrote:
...
> I don't think the OP is dealing with spectrums as much as he is
> dealing with IF of the signals. Not sure but from what I have read on
> the subject I believe this. I would be happy to hear the reply from
> the OP.
I meant to ask before. It can't be "intermediate frequency". What does
IF mean here?
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Jerry Avins●January 27, 20122012-01-27
On 1/27/2012 6:47 AM, Rick Lyons wrote:
> On Fri, 27 Jan 2012 03:50:08 -0500, robert bristow-johnson
> <rbj@audioimagination.com> wrote:
>
>> On 1/26/12 9:58 PM, Rick Lyons wrote:
>>> On Tue, 24 Jan 2012 09:21:59 -0600, "marieclare"
>>> <marieclare.mccormick@n_o_s_p_a_m.uws.ac.uk> wrote:
>>>
>>>> I am using MATLAB to analyse EMG signals. So far I have rectified the data
>>>> and performed a STFT (using a Hamming Window). I am now looking to
>>>> calculate the median frequency of the power spectrum and would be grateful
>>>> if someone could advise me on the best way to do this.
>>>>
>>>> Thanks
>>>
>>> Hello marieclare,
>>> If you have signal, let's call it signal "A".
>>> If you rectify signal "A" you have a different signal
>>> that we'll call signal "B". I hope you
>>> realize that the spectrum of signal "A" will not
>>> be the same as the spectrum of signal "B".
>>>
>>
>> oh c'mon Rick, you're not saying that two signals need be at all alike
>> to have the same spectrum. say A is a dirac impulse and B is white
>> noise. two impossible signals with real-world approximations that have
>> nothing to do with each other except, um, i forgot.
>
> Hi Robert,
> no, I sure didn't mean to imply that two signals need
> be at all alike to have the same spectrum. Perhaps
> I misunderstood the original poster. It just seemed odd
> to me that he said he's analyzing an EMG signal and I
> assumed by "analyzing" he meant spectrum analysis.
> And then he said he was rectifying the EMG signal, and
> that would produce a signal with a different spectrum
> than the spectrum of the original EMG signal. I was merely
> trying to point that out to the original poster.
>
> Being that I know nothing about analyzing EMG signals,
> perhaps I should just keep quiet.
I don't know how modern analyses of EMGs are done, but I suspect that
the term "rectify" here isn't related to absolute values, but maybe to
taking the tilt out of the baseline. I've heard it used that way in
Auger spectrometry.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Mac Decman●January 27, 20122012-01-27
On Fri, 27 Jan 2012 03:47:42 -0800, Rick Lyons
<R.Lyons@_BOGUS_ieee.org> wrote:
>On Fri, 27 Jan 2012 03:50:08 -0500, robert bristow-johnson
><rbj@audioimagination.com> wrote:
>
>>On 1/26/12 9:58 PM, Rick Lyons wrote:
>>> On Tue, 24 Jan 2012 09:21:59 -0600, "marieclare"
>>> <marieclare.mccormick@n_o_s_p_a_m.uws.ac.uk> wrote:
>>>
>>>> I am using MATLAB to analyse EMG signals. So far I have rectified the data
>>>> and performed a STFT (using a Hamming Window). I am now looking to
>>>> calculate the median frequency of the power spectrum and would be grateful
>>>> if someone could advise me on the best way to do this.
>>>>
>>>> Thanks
>>>
>>> Hello marieclare,
>>> If you have signal, let's call it signal "A".
>>> If you rectify signal "A" you have a different signal
>>> that we'll call signal "B". I hope you
>>> realize that the spectrum of signal "A" will not
>>> be the same as the spectrum of signal "B".
>>>
>>
>>oh c'mon Rick, you're not saying that two signals need be at all alike
>>to have the same spectrum. say A is a dirac impulse and B is white
>>noise. two impossible signals with real-world approximations that have
>>nothing to do with each other except, um, i forgot.
>
>Hi Robert,
> no, I sure didn't mean to imply that two signals need
>be at all alike to have the same spectrum. Perhaps
>I misunderstood the original poster. It just seemed odd
>to me that he said he's analyzing an EMG signal and I
>assumed by "analyzing" he meant spectrum analysis.
>And then he said he was rectifying the EMG signal, and
>that would produce a signal with a different spectrum
>than the spectrum of the original EMG signal. I was merely
>trying to point that out to the original poster.
>
>Being that I know nothing about analyzing EMG signals,
>perhaps I should just keep quiet.
>
>See Ya',
>[-Rick-]
>
>
>
>
I don't think the OP is dealing with spectrums as much as he is
dealing with IF of the signals. Not sure but from what I have read on
the subject I believe this. I would be happy to hear the reply from
the OP.
Mark DeArman
Reply by Rick Lyons●January 27, 20122012-01-27
On Fri, 27 Jan 2012 03:50:08 -0500, robert bristow-johnson
<rbj@audioimagination.com> wrote:
>On 1/26/12 9:58 PM, Rick Lyons wrote:
>> On Tue, 24 Jan 2012 09:21:59 -0600, "marieclare"
>> <marieclare.mccormick@n_o_s_p_a_m.uws.ac.uk> wrote:
>>
>>> I am using MATLAB to analyse EMG signals. So far I have rectified the data
>>> and performed a STFT (using a Hamming Window). I am now looking to
>>> calculate the median frequency of the power spectrum and would be grateful
>>> if someone could advise me on the best way to do this.
>>>
>>> Thanks
>>
>> Hello marieclare,
>> If you have signal, let's call it signal "A".
>> If you rectify signal "A" you have a different signal
>> that we'll call signal "B". I hope you
>> realize that the spectrum of signal "A" will not
>> be the same as the spectrum of signal "B".
>>
>
>oh c'mon Rick, you're not saying that two signals need be at all alike
>to have the same spectrum. say A is a dirac impulse and B is white
>noise. two impossible signals with real-world approximations that have
>nothing to do with each other except, um, i forgot.
Hi Robert,
no, I sure didn't mean to imply that two signals need
be at all alike to have the same spectrum. Perhaps
I misunderstood the original poster. It just seemed odd
to me that he said he's analyzing an EMG signal and I
assumed by "analyzing" he meant spectrum analysis.
And then he said he was rectifying the EMG signal, and
that would produce a signal with a different spectrum
than the spectrum of the original EMG signal. I was merely
trying to point that out to the original poster.
Being that I know nothing about analyzing EMG signals,
perhaps I should just keep quiet.
See Ya',
[-Rick-]
Reply by robert bristow-johnson●January 27, 20122012-01-27
On 1/26/12 9:58 PM, Rick Lyons wrote:
> On Tue, 24 Jan 2012 09:21:59 -0600, "marieclare"
> <marieclare.mccormick@n_o_s_p_a_m.uws.ac.uk> wrote:
>
>> I am using MATLAB to analyse EMG signals. So far I have rectified the data
>> and performed a STFT (using a Hamming Window). I am now looking to
>> calculate the median frequency of the power spectrum and would be grateful
>> if someone could advise me on the best way to do this.
>>
>> Thanks
>
> Hello marieclare,
> If you have signal, let's call it signal "A".
> If you rectify signal "A" you have a different signal
> that we'll call signal "B". I hope you
> realize that the spectrum of signal "A" will not
> be the same as the spectrum of signal "B".
>
oh c'mon Rick, you're not saying that two signals need be at all alike
to have the same spectrum. say A is a dirac impulse and B is white
noise. two impossible signals with real-world approximations that have
nothing to do with each other except, um, i forgot.
--
r b-j rbj@audioimagination.com
"Imagination is more important than knowledge."