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A simple audio-filter

I need to find a way to build a simple audio filter. It's for an electronic talking toy which uses a piezo-speaker. I've removed the speaker and tried to make a line-out instead, but the sound is pretty "gritty" and "dirty". I believe I can make it better with some adjustments (filtering) This is what I've done so far:

220K 10nF ----------------->---------------o---xxxx----o o--||----->

| | 50K x | audio Audio x-------------------------------o----------------->

I've experimented with different capacitors. If I lower the value (say

6 nF) the bass goes away (which includes some low frequency "rumble") and I get more treble. If I insert a capacitor with a higher value (say 40 nF) the opposite happens. I would like to remove the annoying "rumble" and "dirty" part of the sound, but without removing all of the bass in the process. How do I do this in the simplest possible way?
Reply to
Arild P.
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The simplest possible way is to get a different transducer. Is it really a "piezo speaker", or is it merely a piezo sounder - those are usually used at their resonant frequency, and the frequency response is crap.

If you're using a "real" piezo "speaker", then you have a tweeter and you're never going to get decent bass out of it anyway.

Good Luck! Rich

Reply to
Rich Grise

It occured to me that explaining audio with words isn't the way to do it, so I've uploaded some MP3 examples:

First, here's the type of sound I want to end up with (I'm using a similar toy here which does indeed have a headphone output):

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But here's the toy I'm working on, trying to add a suitable line-output, having removed the piezo-ceramic speaker from its audio output and added my line-out circuit, but without any capacitor:

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Notice the very "harsh" and "dirty" sound compared to my reference.

Here's the same toy with a 10nF capacitor which filters away a lot of the "harshness", but also removes more:

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To make it easier to compare, here are the two toys saying the same word. First the "reference" toy:

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Now the other toy:

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My question is, how do I make the "dirty sounding" toy sound more or less like the "clean" one?

Reply to
Arild P.

I'm not sure what it's called. Piezo something. I've googled for an image which I've found here, which looks similar to what my toy uses:

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The speaker/transducer/sounder or whatever is marked:

Murata VSB41D25-07AR

I couldn't find any specifications online. I'm sure it's long since been discontinued since the toy is from the 80s.

The problem is that I seem to actually be getting too much bass out of it! I've just made and uploaded some MP3 files which will explain a lot more along with a new posting.

Reply to
Arild P.

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