Comments on: filtering pwm for music http://www.workinprogress.ca/filtering-pwm-for-music/ of patrick sébastien coulombe Mon, 19 Jul 2010 10:30:44 -0400 hourly 1 http://wordpress.org/?v=3.0 By: psc http://www.workinprogress.ca/filtering-pwm-for-music/comment-page-1/#comment-183 psc Thu, 18 Mar 2010 04:02:57 +0000 http://www.workinprogress.ca/?p=581#comment-183 I still can't help you out, but i am very curious. The keywords i found are: <a href="http://en.wikipedia.org/wiki/Reconstruction_filter" rel="nofollow">Reconstruction filter</a> <a href="http://en.wikipedia.org/wiki/Buffer_amplifier" rel="nofollow">Output buffer</a> From this <a href="http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/DDS.pdf" rel="nofollow">application note</a>: <em>A seventh degree Bessel filter, with a −3 dB cutoffof, 2f, f fc = fs/4, is a good choice for filtering arbitrary waveforms. This filter will exhibit an output risetime of 0.35/fc.</em> I still can’t help you out, but i am very curious. The keywords i found are:
Reconstruction filter
Output buffer

From this application note:
A seventh degree Bessel filter, with a −3 dB cutoffof, 2f, f fc = fs/4, is a good choice for filtering arbitrary waveforms. This filter will exhibit an output risetime of 0.35/fc.

]]> By: Gorkem http://www.workinprogress.ca/filtering-pwm-for-music/comment-page-1/#comment-182 Gorkem Tue, 16 Mar 2010 21:29:11 +0000 http://www.workinprogress.ca/?p=581#comment-182 Thank you very much for your answer. I am using a DAC. It generates 50Hz to 8kHz. It has high freq noise components but it works. I wonder what kind of filter I can use above 2khz. Because after 2khz a big capacitive effect occurs on signal. For example a sawtooth or a triangle wave turns to a sine. Also I am planning to use an analog multiplexer to send the (nearly perfect) square wave to output without filtering. And one more question, why band pass filter? Thank you very much for your answer.
I am using a DAC. It generates 50Hz to 8kHz. It has high freq noise components but it works. I wonder what kind of filter I can use above 2khz. Because after 2khz a big capacitive effect occurs on signal. For example a sawtooth or a triangle wave turns to a sine. Also I am planning to use an analog multiplexer to send the (nearly perfect) square wave to output without filtering.
And one more question, why band pass filter?

]]> By: psc http://www.workinprogress.ca/filtering-pwm-for-music/comment-page-1/#comment-181 psc Tue, 16 Mar 2010 18:42:37 +0000 http://www.workinprogress.ca/?p=581#comment-181 Hello Gorkem, My knowledge in analog filter is very limited... Your signal generator is using a DAC or PWM? Are you sure that your MC is fast enough? Maybe you will need to use a <a href="http://en.wikipedia.org/wiki/Band-pass_filter" rel="nofollow">band-pass filter</a>? Hello Gorkem,
My knowledge in analog filter is very limited…

Your signal generator is using a DAC or PWM?
Are you sure that your MC is fast enough?
Maybe you will need to use a band-pass filter?

]]> By: Gorkem http://www.workinprogress.ca/filtering-pwm-for-music/comment-page-1/#comment-180 Gorkem Mon, 15 Mar 2010 20:00:17 +0000 http://www.workinprogress.ca/?p=581#comment-180 Hello, I would like to ask you something. I am designing a signal generator. It works between 50Hz-8kHz freq range. I used a sallen key lowpass (fc=8kHz) but I have some problems. Below 600Hz it has no effect on signal. Also above 1kHz a huge disturbance occurs. I will be grateful if I can take some answers or suggestions. Thank you, Gorkem Hello, I would like to ask you something. I am designing a signal generator. It works between 50Hz-8kHz freq range. I used a sallen key lowpass (fc=8kHz) but I have some problems. Below 600Hz it has no effect on signal. Also above 1kHz a huge disturbance occurs. I will be grateful if I can take some answers or suggestions.

Thank you,
Gorkem

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