Operational Transconductance Amplifier (OTA)

[xmat]

High guys.

Currently building a common slope detector (differentiator) with an ordinary o-pamp..

I was wondering, could I change the common opamp with an OTA (Operational Transconductance Amplifier) like LM13700 and achieve an "adaptive center weighted median filter" to act as state-variable slope detector (i.e parameter to adjust would be slope, not frequency)??

I want it to filter out "impulsive noise" from audio sources (a rythm song), such as clicks and pops on vinyl records..Understand?

Thanks in advance,

xmat.

PS: Some circuit references (such as from NS application hints) would be great...

 

[Nigel Goodwin]

I want it to filter out "impulsive noise" from audio sources (a rythm song), such as clicks and pops on vinyl records..Understand?

That doesn't sound a very useful way to do it?, there have been many designs (both commercial and homebuilt) over the years for removing clicks from records.

There are basically two problems, firstly detecting the click (this can be done by detecting a fast rise time), secondly muting the click at the correct moment (because by the time you've detected the click it's too late).

The usual solution was to use bucket brigade devices as a time delay, delaying the sound a few milliseconds - you then feed the click detector into an adjustable monostable, so you can adjust the timing so it removes the click at the correct instant.

They actually worked really well! - the problem now is finding the bucket brigade delay chips, they seem to have been discontinued. But you could do a similar thing by digitising the audio and moving it along through memory chips, then convert it back to analogue.

 

[williB]

But you could do a similar thing by digitizing the audio and moving it along through memory chips, then convert it back to analogue.

thats what i would do..and it is soooo much easier..
Plus you have the sound card allready..!!
just save the recording from the record to a wave file ..and just delete the pops and blips..
you could probably also reconstruct the wave behind the clicks by taking a sample of a similiar part of the origional and splicing it in....

 

[zevon8]

Many of the Creative Labs sound cards come with some very usefull sofware that can be used for this purpose. You can visually display the sound waveform, and edit , cut paste, apply filters, reverse, echo, etc, etc.

The audio appears in a real time display that can be zoomed, making it very easy to modify using a cursor system.

 

[Dr.EM]

Oh yeah, that is the best way to do it. I have that wav editor software, it comes with most Audigy cards. I would go through, and if you find a click, don't just delete it, but apply a fade in effect (1% magnitude) on it, this will basically defeat it but without causing a dropout in the track.

 

[xmat]

thanks

Thanks for the responses, guys.

I am aware of the digital solutions out there for such application, I just want to see if I can achieve an analog one..

..Plus I was curious of whether the following could happen:

If I place an OTA (instead an ordinary o-pamp) into a differentiator (i.e slope detector),
can I achieve an "adaptive center weighted median filter" that will act as an "adaptive slope detector" (i.e the parameter that is center weighted/adjusted is slope)

Just a question for OTA experts..born due to curiosity.

Hope someone could suggest a solution.

Thanks again,

xmat.