RE: 60 hz - any suggestions

[Guest guest]

,

I'm trying to reproduce what you are describing below and getting confused. I don't see how you have a " notch " filter that stands between the source and all other filters. I would assume a notch filter would filter out something like 58-62 Hz, which means it would remove all the other activity (the activity you wanted to actually train and see).

Using a lowpass FIR filter with a 58 cutoff and a 55 length would allow everything to pass up to about 50 Hz, and it should be fairly low impact in terms of delay--perhaps less that the 100ms the " notch " filter would produce.

Can you explain this a little more to me?

Thanks,

pete

Your response makes it sound as though the BMr notch filter just effects the display of raw signal display and not the signal going to band pass filters. Is that actually the case?

In BioExplorer I have implemented a notch filter for use in the few cases where I have found it impossible to get rid of the 60 Hz. I send the filtered info to the band pass filters. It creates a small delay, much less than a low pass filter would.

In response to the post regarding the person (Larry ?) who added a low pass filter to a design while a client was training and saw some big changes in the coherence values it might be partly do to the filter choice in the filter. The default filter is butterworth which has unequal delay across the filtered band. It might look different if an FIR filter was used.

..-- Van Deusenpvdtlc@...http://www.brain-trainer.com

305/433-3160The Learning Curve, Inc.

[Guest guest]

,

I'm trying to reproduce what you are describing below and getting confused. I don't see how you have a " notch " filter that stands between the source and all other filters. I would assume a notch filter would filter out something like 58-62 Hz, which means it would remove all the other activity (the activity you wanted to actually train and see).

Using a lowpass FIR filter with a 58 cutoff and a 55 length would allow everything to pass up to about 50 Hz, and it should be fairly low impact in terms of delay--perhaps less that the 100ms the " notch " filter would produce.

Can you explain this a little more to me?

Thanks,

pete

Your response makes it sound as though the BMr notch filter just effects the display of raw signal display and not the signal going to band pass filters. Is that actually the case?

In BioExplorer I have implemented a notch filter for use in the few cases where I have found it impossible to get rid of the 60 Hz. I send the filtered info to the band pass filters. It creates a small delay, much less than a low pass filter would.

In response to the post regarding the person (Larry ?) who added a low pass filter to a design while a client was training and saw some big changes in the coherence values it might be partly do to the filter choice in the filter. The default filter is butterworth which has unequal delay across the filtered band. It might look different if an FIR filter was used.

..-- Van Deusenpvdtlc@...http://www.brain-trainer.com

305/433-3160The Learning Curve, Inc.

[Guest guest]

Pete,Two outputs from a single source.  One goes straight to input one of expression evaluator.  The other to a 59-61 hz bandpass filter.  Filter sends signal to input two of the expression evlauator.  Expression is in1-in2.  That output goes to the oscilloscope and to the designs bandpass filters. georgemartin@...www.northstarneurofeedback.com , I'm trying to reproduce what you are describing below and getting confused.  I don't see how you have a "notch" filter that stands between the source and all other filters.  I would assume a notch filter would filter out something like 58-62 Hz, which means it would remove all the other activity (the activity you wanted to actually train and see).  Using a lowpass FIR filter with a 58 cutoff and a 55 length would allow everything to pass up to about 50 Hz, and it should be fairly low impact in terms of delay--perhaps less that the 100ms the "notch" filter would produce. Can you explain this a little more to me? Thanks, peteYour response makes it sound as though the BMr notch filter just effects the display of raw signal display and not the signal going to band pass filters. Is that actually the case?In BioExplorer I have implemented a notch filter for use in the few cases where I have found it impossible to get rid of the 60 Hz.  I send the filtered info to the band pass filters.  It creates a small delay, much less than a low pass filter would.In response to the post regarding the person (Larry ?) who added a low pass filter to a design while a client was training and saw some big changes in the coherence values it might be partly do to the filter choice in the filter.  The default filter is butterworth which has unequal delay across the filtered band.  It might look different if an FIR filter was used..--  Van Deusenpvdtlc@...http://www.brain-trainer.com305/433-3160The Learning Curve, Inc. 

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[Guest guest]

Pete,Two outputs from a single source.  One goes straight to input one of expression evaluator.  The other to a 59-61 hz bandpass filter.  Filter sends signal to input two of the expression evlauator.  Expression is in1-in2.  That output goes to the oscilloscope and to the designs bandpass filters. georgemartin@...www.northstarneurofeedback.com , I'm trying to reproduce what you are describing below and getting confused.  I don't see how you have a "notch" filter that stands between the source and all other filters.  I would assume a notch filter would filter out something like 58-62 Hz, which means it would remove all the other activity (the activity you wanted to actually train and see).  Using a lowpass FIR filter with a 58 cutoff and a 55 length would allow everything to pass up to about 50 Hz, and it should be fairly low impact in terms of delay--perhaps less that the 100ms the "notch" filter would produce. Can you explain this a little more to me? Thanks, peteYour response makes it sound as though the BMr notch filter just effects the display of raw signal display and not the signal going to band pass filters. Is that actually the case?In BioExplorer I have implemented a notch filter for use in the few cases where I have found it impossible to get rid of the 60 Hz.  I send the filtered info to the band pass filters.  It creates a small delay, much less than a low pass filter would.In response to the post regarding the person (Larry ?) who added a low pass filter to a design while a client was training and saw some big changes in the coherence values it might be partly do to the filter choice in the filter.  The default filter is butterworth which has unequal delay across the filtered band.  It might look different if an FIR filter was used..--  Van Deusenpvdtlc@...http://www.brain-trainer.com305/433-3160The Learning Curve, Inc. 

--- Get FREE High Speed Internet from USFamily.Net! ---

[Guest guest]

Pete,Two outputs from a single source.  One goes straight to input one of expression evaluator.  The other to a 59-61 hz bandpass filter.  Filter sends signal to input two of the expression evlauator.  Expression is in1-in2.  That output goes to the oscilloscope and to the designs bandpass filters. georgemartin@...www.northstarneurofeedback.com , I'm trying to reproduce what you are describing below and getting confused.  I don't see how you have a "notch" filter that stands between the source and all other filters.  I would assume a notch filter would filter out something like 58-62 Hz, which means it would remove all the other activity (the activity you wanted to actually train and see).  Using a lowpass FIR filter with a 58 cutoff and a 55 length would allow everything to pass up to about 50 Hz, and it should be fairly low impact in terms of delay--perhaps less that the 100ms the "notch" filter would produce. Can you explain this a little more to me? Thanks, peteYour response makes it sound as though the BMr notch filter just effects the display of raw signal display and not the signal going to band pass filters. Is that actually the case?In BioExplorer I have implemented a notch filter for use in the few cases where I have found it impossible to get rid of the 60 Hz.  I send the filtered info to the band pass filters.  It creates a small delay, much less than a low pass filter would.In response to the post regarding the person (Larry ?) who added a low pass filter to a design while a client was training and saw some big changes in the coherence values it might be partly do to the filter choice in the filter.  The default filter is butterworth which has unequal delay across the filtered band.  It might look different if an FIR filter was used..--  Van Deusenpvdtlc@...http://www.brain-trainer.com305/433-3160The Learning Curve, Inc. 

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[Guest guest]

Hi,

I do not have a suggestion I have a question while we are on the 60 hz subject. I am in the works on getting ready to do my written boards for EEG this fall and have been doing EEG in a neurologist office until he has a stroke and passed away, then I moved the last two years to the local hospital. I have been talking with a few different registered tech's about his matter and they have different opinions.

Now of course we always try to find the source of the 60 hz and remove it that way, but sometimes while working in CCU there are so many machines going it can be very difficult to do that so our next source to remove it would be the notch filter.

Some are saying if you leave your notch filter off you are hiding the background with the 60 hz and you should leave it on to what some make a pretty recording. My concern is you can change filters during review but you can not turn on or off the notch filter during review.

Some others are now saying that if you turn your notch filter on that you take the chance of covering up spikes and slow waves so you should turn it on for a short time and then turn it back off proving it is 60 hz but then run the rest of the recording with the notch filter off and deal with the 60 hz.

The machines we are working on are Cadwell Easy Two.

OH one suggestion that I have picked up from one tech and it has worked at times, is take you ground wire and unplug it from the head box, wrap that wire around the rest of the your wires about 2 to 3 times and then plug it back in, amazing how often this does work. Others could be hair under your electrode and of course the bad wire or electrode as well.

Thanks,

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[Guest guest]

Hi,

I do not have a suggestion I have a question while we are on the 60 hz subject. I am in the works on getting ready to do my written boards for EEG this fall and have been doing EEG in a neurologist office until he has a stroke and passed away, then I moved the last two years to the local hospital. I have been talking with a few different registered tech's about his matter and they have different opinions.

Now of course we always try to find the source of the 60 hz and remove it that way, but sometimes while working in CCU there are so many machines going it can be very difficult to do that so our next source to remove it would be the notch filter.

Some are saying if you leave your notch filter off you are hiding the background with the 60 hz and you should leave it on to what some make a pretty recording. My concern is you can change filters during review but you can not turn on or off the notch filter during review.

Some others are now saying that if you turn your notch filter on that you take the chance of covering up spikes and slow waves so you should turn it on for a short time and then turn it back off proving it is 60 hz but then run the rest of the recording with the notch filter off and deal with the 60 hz.

The machines we are working on are Cadwell Easy Two.

OH one suggestion that I have picked up from one tech and it has worked at times, is take you ground wire and unplug it from the head box, wrap that wire around the rest of the your wires about 2 to 3 times and then plug it back in, amazing how often this does work. Others could be hair under your electrode and of course the bad wire or electrode as well.

Thanks,

Wondering what's for Dinner Tonight? Get new twists on family favorites at AOL Food.

[Guest guest]

Hi,

I do not have a suggestion I have a question while we are on the 60 hz subject. I am in the works on getting ready to do my written boards for EEG this fall and have been doing EEG in a neurologist office until he has a stroke and passed away, then I moved the last two years to the local hospital. I have been talking with a few different registered tech's about his matter and they have different opinions.

Now of course we always try to find the source of the 60 hz and remove it that way, but sometimes while working in CCU there are so many machines going it can be very difficult to do that so our next source to remove it would be the notch filter.

Some are saying if you leave your notch filter off you are hiding the background with the 60 hz and you should leave it on to what some make a pretty recording. My concern is you can change filters during review but you can not turn on or off the notch filter during review.

Some others are now saying that if you turn your notch filter on that you take the chance of covering up spikes and slow waves so you should turn it on for a short time and then turn it back off proving it is 60 hz but then run the rest of the recording with the notch filter off and deal with the 60 hz.

The machines we are working on are Cadwell Easy Two.

OH one suggestion that I have picked up from one tech and it has worked at times, is take you ground wire and unplug it from the head box, wrap that wire around the rest of the your wires about 2 to 3 times and then plug it back in, amazing how often this does work. Others could be hair under your electrode and of course the bad wire or electrode as well.

Thanks,

Wondering what's for Dinner Tonight? Get new twists on family favorites at AOL Food.

[Guest guest]

Active

electrodes got rid of mine after I had tried everything else. More expense but

it worked

Cheers Tony

Re: 60 hz

- any suggestions

Hi,

I do

not have a suggestion I have a question while we are on the 60 hz subject. I am

in the works on getting ready to do my written boards for EEG this fall and

have been doing EEG in a neurologist office until he has a stroke and passed

away, then I moved the last two years to the local hospital. I have been

talking with a few different registered tech's about his matter and they have

different opinions.

Now of

course we always try to find the source of the 60 hz and remove it that way,

but sometimes while working in CCU there are so many machines going it can be

very difficult to do that so our next source to remove it would be the notch

filter.

Some

are saying if you leave your notch filter off you are hiding the background

with the 60 hz and you should leave it on to what some make a pretty recording.

My concern is you can change filters during review but you can not turn on or

off the notch filter during review.

Some

others are now saying that if you turn your notch filter on that you take the

chance of covering up spikes and slow waves so you should turn it on for a

short time and then turn it back off proving it is 60 hz but then run the rest

of the recording with the notch filter off and deal with the 60 hz.

The

machines we are working on are Cadwell Easy Two.

OH one

suggestion that I have picked up from one tech and it has worked at times, is

take you ground wire and unplug it from the head box, wrap that wire around the

rest of the your wires about 2 to 3 times and then plug it back in, amazing how

often this does work. Others could be hair under your electrode and of course

the bad wire or electrode as well.

Thanks,

Wondering

what's for Dinner Tonight? Get new

twists on family favorites at AOL Food.

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[Guest guest]

Try wrapping a turn or two of each probe wire around a ferrite bead (one for each probe) available at radio shack probably in their small parts bin. Also locate the ferrite beads (torroid core) as close to the amp as possible. Randy Van Deusen wrote: , I am saying that it's valuable to know if the 60 Hz signal (or 50 Hz in many parts of the world) is present or not. The

notch filter covers it up and it does remove it from the signal. The problem I am speaking about is that, at least from what I have seen, a strong 60 Hz signal will affect the level of coherence in high frequencies well below 60 Hz. Also, that removing the signal at 60 Hz does seem to have an effect on other FAST frequencies. It shouldn't have any effect on slow frequencies. The suggestions you were given (make sure there is no hair under electrodes and that electrodes are in good shape) are very basic and exactly what I was recommending: get a good clean connection to the scalp first, and there is less opportunity for the 60 Hz signal to enter. Also, if you are using an electrical source with no ground or a bad ground (not the EEG machine but the wall circuit), by removing the computer from that source you can also often get rid of the problem. Braiding the electrodes, so they wrap around each other (or wrapping

the other electrodes with the ground as was suggested to you) is also a commonly used way or reducing the "antenna" effect of the electrodes--as is using shorter electrode wires. All these are related to removing the opportunity for the "mains" signal (coming from the electrical mains) from entering the EEG signal. This is what I am saying is the ideal way to deal with it. And I know that and others who have posted on this topic know that very well. My concern is that many trainers are lulled into a false sense of security by things like notch filters which make a signal look more clean than it really is. Thanks for your input. Pete On Tue, May 6, 2008 at 12:04 AM, <CMsHippityHopsaol> wrote: I do not have a suggestion I have a question while we are on the 60 hz subject. I am in the works on getting ready to do my written boards for EEG this fall and have been doing EEG in a neurologist office until he has a stroke and passed away, then I moved the last two years to the local hospital. I have been talking with a few different registered tech's about his matter and they have different opinions. Now of course we always try to find the source of the 60 hz and remove it that way, but sometimes while working in CCU there are so many machines going it can be very difficult to do that so our next source to remove it would be the notch filter. Some are saying if you leave your notch filter off you are hiding the background with the 60 hz and you should leave it on to what some make a pretty recording. My concern is you can change filters during

review but you can not turn on or off the notch filter during review. Some others are now saying that if you turn your notch filter on that you take the chance of covering up spikes and slow waves so you should turn it on for a short time and then turn it back off proving it is 60 hz but then run the rest of the recording with the notch filter off and deal with the 60 hz. The machines we are working on are Cadwell Easy Two. OH one suggestion that I have picked up from one tech and it has worked at times, is take you ground wire and unplug it from the head box, wrap that wire around the rest of the your wires about 2 to 3 times and then plug it back in, amazing how often this does work. Others could be hair under your electrode and of course the bad wire or electrode as well. Messages in this topic (13) Reply (via web post) | Start a new topic Messages | Calendar Change settings via the Web (Yahoo! ID required) Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe ._._,___ -- Van Deusenpvdtlcgmailhttp://www.brain-trainer.com305/433-3160The Learning Curve, Inc.

Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now.

[Guest guest]

Try wrapping a turn or two of each probe wire around a ferrite bead (one for each probe) available at radio shack probably in their small parts bin. Also locate the ferrite beads (torroid core) as close to the amp as possible. Randy Van Deusen wrote: , I am saying that it's valuable to know if the 60 Hz signal (or 50 Hz in many parts of the world) is present or not. The

notch filter covers it up and it does remove it from the signal. The problem I am speaking about is that, at least from what I have seen, a strong 60 Hz signal will affect the level of coherence in high frequencies well below 60 Hz. Also, that removing the signal at 60 Hz does seem to have an effect on other FAST frequencies. It shouldn't have any effect on slow frequencies. The suggestions you were given (make sure there is no hair under electrodes and that electrodes are in good shape) are very basic and exactly what I was recommending: get a good clean connection to the scalp first, and there is less opportunity for the 60 Hz signal to enter. Also, if you are using an electrical source with no ground or a bad ground (not the EEG machine but the wall circuit), by removing the computer from that source you can also often get rid of the problem. Braiding the electrodes, so they wrap around each other (or wrapping

the other electrodes with the ground as was suggested to you) is also a commonly used way or reducing the "antenna" effect of the electrodes--as is using shorter electrode wires. All these are related to removing the opportunity for the "mains" signal (coming from the electrical mains) from entering the EEG signal. This is what I am saying is the ideal way to deal with it. And I know that and others who have posted on this topic know that very well. My concern is that many trainers are lulled into a false sense of security by things like notch filters which make a signal look more clean than it really is. Thanks for your input. Pete On Tue, May 6, 2008 at 12:04 AM, <CMsHippityHopsaol> wrote: I do not have a suggestion I have a question while we are on the 60 hz subject. I am in the works on getting ready to do my written boards for EEG this fall and have been doing EEG in a neurologist office until he has a stroke and passed away, then I moved the last two years to the local hospital. I have been talking with a few different registered tech's about his matter and they have different opinions. Now of course we always try to find the source of the 60 hz and remove it that way, but sometimes while working in CCU there are so many machines going it can be very difficult to do that so our next source to remove it would be the notch filter. Some are saying if you leave your notch filter off you are hiding the background with the 60 hz and you should leave it on to what some make a pretty recording. My concern is you can change filters during

review but you can not turn on or off the notch filter during review. Some others are now saying that if you turn your notch filter on that you take the chance of covering up spikes and slow waves so you should turn it on for a short time and then turn it back off proving it is 60 hz but then run the rest of the recording with the notch filter off and deal with the 60 hz. The machines we are working on are Cadwell Easy Two. OH one suggestion that I have picked up from one tech and it has worked at times, is take you ground wire and unplug it from the head box, wrap that wire around the rest of the your wires about 2 to 3 times and then plug it back in, amazing how often this does work. Others could be hair under your electrode and of course the bad wire or electrode as well. Messages in this topic (13) Reply (via web post) | Start a new topic Messages | Calendar Change settings via the Web (Yahoo! ID required) Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe ._._,___ -- Van Deusenpvdtlcgmailhttp://www.brain-trainer.com305/433-3160The Learning Curve, Inc.

Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now.

[Guest guest]

Try wrapping a turn or two of each probe wire around a ferrite bead (one for each probe) available at radio shack probably in their small parts bin. Also locate the ferrite beads (torroid core) as close to the amp as possible. Randy Van Deusen wrote: , I am saying that it's valuable to know if the 60 Hz signal (or 50 Hz in many parts of the world) is present or not. The

notch filter covers it up and it does remove it from the signal. The problem I am speaking about is that, at least from what I have seen, a strong 60 Hz signal will affect the level of coherence in high frequencies well below 60 Hz. Also, that removing the signal at 60 Hz does seem to have an effect on other FAST frequencies. It shouldn't have any effect on slow frequencies. The suggestions you were given (make sure there is no hair under electrodes and that electrodes are in good shape) are very basic and exactly what I was recommending: get a good clean connection to the scalp first, and there is less opportunity for the 60 Hz signal to enter. Also, if you are using an electrical source with no ground or a bad ground (not the EEG machine but the wall circuit), by removing the computer from that source you can also often get rid of the problem. Braiding the electrodes, so they wrap around each other (or wrapping

the other electrodes with the ground as was suggested to you) is also a commonly used way or reducing the "antenna" effect of the electrodes--as is using shorter electrode wires. All these are related to removing the opportunity for the "mains" signal (coming from the electrical mains) from entering the EEG signal. This is what I am saying is the ideal way to deal with it. And I know that and others who have posted on this topic know that very well. My concern is that many trainers are lulled into a false sense of security by things like notch filters which make a signal look more clean than it really is. Thanks for your input. Pete On Tue, May 6, 2008 at 12:04 AM, <CMsHippityHopsaol> wrote: I do not have a suggestion I have a question while we are on the 60 hz subject. I am in the works on getting ready to do my written boards for EEG this fall and have been doing EEG in a neurologist office until he has a stroke and passed away, then I moved the last two years to the local hospital. I have been talking with a few different registered tech's about his matter and they have different opinions. Now of course we always try to find the source of the 60 hz and remove it that way, but sometimes while working in CCU there are so many machines going it can be very difficult to do that so our next source to remove it would be the notch filter. Some are saying if you leave your notch filter off you are hiding the background with the 60 hz and you should leave it on to what some make a pretty recording. My concern is you can change filters during

review but you can not turn on or off the notch filter during review. Some others are now saying that if you turn your notch filter on that you take the chance of covering up spikes and slow waves so you should turn it on for a short time and then turn it back off proving it is 60 hz but then run the rest of the recording with the notch filter off and deal with the 60 hz. The machines we are working on are Cadwell Easy Two. OH one suggestion that I have picked up from one tech and it has worked at times, is take you ground wire and unplug it from the head box, wrap that wire around the rest of the your wires about 2 to 3 times and then plug it back in, amazing how often this does work. Others could be hair under your electrode and of course the bad wire or electrode as well. Messages in this topic (13) Reply (via web post) | Start a new topic Messages | Calendar Change settings via the Web (Yahoo! ID required) Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe ._._,___ -- Van Deusenpvdtlcgmailhttp://www.brain-trainer.com305/433-3160The Learning Curve, Inc.

Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now.