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Old 6th December 2012, 05:47 PM   #1
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Default Filter Bass and treble to the input of a microprocessor

Hey there,

Let me first start by apologizing if this is the wrong place to post this,
I have very little knowledge on audio things.

I have been trying to learn how to use an arduino, microprocessors, circuits, etc. for a few months now. I am currently working on a project where I essentially need to filter out treble and leave the bass of audio going through headphones (so there is no amplifier involved.)

I need the filter to filter OUT the audio and leave the bass, not make all of the audio have a lower frequency. Im sure you guys know what I mean.

Does anyone know of a simple easy to follow circuit to do this?

I appreciate the help!
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Old 6th December 2012, 06:04 PM   #2
Mooly is offline Mooly  United Kingdom
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No apologies neccessary

I've put this in analogue line level as I assumed you are working in the analogue domain with the filtering ?

(It can always be moved again if not)
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Old 6th December 2012, 06:07 PM   #3
Mooly is offline Mooly  United Kingdom
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To filter the treble out of the audio feed to headphones as you mention could probably be done with a simple R and C filter as long as there is enough voltage drive available. Very unusual way of doing it mind you but it should work.

Is this what you mean

Or do you mean a digital filter ?
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Old 6th December 2012, 06:27 PM   #4
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nope, an rc filter seems perfect! thanks for the help
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Old 6th December 2012, 06:36 PM   #5
Mooly is offline Mooly  United Kingdom
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Do you know how to arrange it ?

Its basically a series resistor to the phones, one for left and one for right channels. The caps just connect from the phones end of the resistor to ground (in other words across each driver).

No real idea on values (because its an unusual method applying it on a "speaker") but I would start with say 100 ohms and some small caps of say 1uf ? (as a guess).
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Old 6th December 2012, 06:44 PM   #6
Mooly is offline Mooly  United Kingdom
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I've just tried those values in a simulation (assuming say 32 ohms as headphone impedance) and they seem about right as a starting point. You can increase the cap to get more of a treble cut to whatever you wish really but 1uf is a fair starting point.
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Old 6th December 2012, 06:46 PM   #7
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This was 100 ohm and 10uf. You can see the roll off (solid line). For 1uf and the roll off frequency moves up by a factor of 10.
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