Is it stupid to connect DIY filters to a laptop via the audio jack port

...and how to do so...
KVRer
19 posts since 17 Dec, 2020

Post Tue Feb 02, 2021 10:04 am

I would like to build a low pass filter myself. (For fun and learning.)

Now, I would like to take the audio output of my laptop,
pass it through the DIY low pass filter and feed it back into the audio input of my laptop.

Is this doable/safe? I'm afraid that some self-oscillations etc. could harm my laptop...
(I would like to use the laptop since I want to minimise the costs, i.e. I don't want to build a synth from the bottom up.)

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KVRAF
29920 posts since 27 Jul, 2005 from the wilds of wanny

Post Tue Feb 02, 2021 10:09 am

You could get some awful feedback loop if you're not careful, depending on how you are monitoring the resulting signal.

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KVRAF
12782 posts since 8 Mar, 2005 from Utrecht, Holland

Post Tue Feb 02, 2021 10:21 am

You'll want (need) two stereo outputs: one to feed the filter, another for monitoring other tracks.

If you know what you are doing, it's relatively safe. Having a physical knob to adjust the volume will help. Maybe use a mixer?
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KVRer

Topic Starter

19 posts since 17 Dec, 2020

Post Tue Feb 02, 2021 11:30 am

Thanks for the tips. I don't really know what I'm doing! I had lectures on theoretical electromagnetism, but no hands-on experience.

@BertKoor: Yes, I forgot that part. I don't have a mixer or any kind of audio interface. Just one Laptop audio jack.
In this case, I might directly forward the filter output signal to my headphones. It would be ok for me to have only filtered sound or maybe a switch to bypass the filter for comparison.

That's basically what I want to build first. Afterwards, I can make it more complicated.
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KVRAF
4415 posts since 22 Jul, 2006 from Tasmania, Australia

Post Tue Feb 02, 2021 12:10 pm

there's nothing wrong with that serial device chain,
there is no feedback at all

hope it works nicely for u!

KVRer

Topic Starter

19 posts since 17 Dec, 2020

Post Tue Feb 02, 2021 12:31 pm

Thanks!

I will come back when I want to do other filters :D Hopefully knowing a bit more then :)

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KVRAF
12782 posts since 8 Mar, 2005 from Utrecht, Holland

Post Tue Feb 02, 2021 1:11 pm

Then you need a headphone amp as well, since the output level of your filter will be line level and not strong enough to drive headphones.

(or get a small mixer with headphone amp included)
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KVRer

Topic Starter

19 posts since 17 Dec, 2020

Post Tue Feb 02, 2021 2:06 pm

I see. Thanks for the hint.

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KVRAF
12782 posts since 8 Mar, 2005 from Utrecht, Holland

Post Tue Feb 02, 2021 11:39 pm

Just saw your diagram of your filter design being just a capacitor and a resistor. That's a passive filter, and I can guarantee you 98% it will be a disappointment. This is the type of tone control used on AM tube radios in my youth and the same type I gutted out of my guitar, because it hardly does anything to the signal. With a bit of luck you can hear a bit diminishment of brilliance, and that's it. The effect is just too subtle and too depending on impedance of the input, impedance of the output, value of the capacitor and value of the resistor.

Mind you: for that 2% chance you like it, it's a nice project. So do try it.
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KVRer

Topic Starter

19 posts since 17 Dec, 2020

Post Wed Feb 03, 2021 2:38 am

It's good to know what to expect. I would still try it :) For me, it's more about getting started with something.

Initially, I wanted to do directly some kind of 2-pole filter, but I thought it's better to start with the bare minimum and then move on. (Obviously, I also have to read more, until know I just skimmed Wikipedia.)

KVRer

Topic Starter

19 posts since 17 Dec, 2020

Post Sun May 16, 2021 12:05 am

Hey,
it took me some while to learn more basics of electronics, but I finally tried the passive low pass filter
and like predicted, it's not too impressive sound-wise, but I had fun and learned something on the way!

Thanks for your hints :)

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KVRAF
12782 posts since 8 Mar, 2005 from Utrecht, Holland

Post Sun May 16, 2021 1:30 am

It's fun indeed.
Thanks for sharing!
We are the KVR collective. Resistance is futile. You will be assimilated. Image
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KVRAF
4470 posts since 22 Nov, 2012

Post Sun May 16, 2021 2:07 pm

do what sounds good. i once took a macbeth M3X and recorded it to laptop, then fed it out of the headphone jack to a tape recorder. it was glorious.

xtp
KVRian
999 posts since 4 Jun, 2006

Post Sun May 16, 2021 2:39 pm

SteffenPL wrote:
Sun May 16, 2021 12:05 am
Hey,
it took me some while to learn more basics of electronics, but I finally tried the passive low pass filter
and like predicted, it's not too impressive sound-wise, but I had fun and learned something on the way!

Thanks for your hints :)
Hi,

Heaps of fun.

I spent about 8 years designing a low volume system for my electric guitar, so I could get the tone I want at about the average volume of an acoustic guitar.

One of the units I use is a lp/hp filter. All of the units I designed are passive and use a follower gain stage as well as buffers ie: buffer (voltage follower) ->Passive filter -> gain stage -> buffer.

You could try replacing the resistor with a pot wired as a variable resistor.

On my hpf, I use a switch with 3 different caps and a pot (I think I had about 8 cap selectors in the original design) that sweeps from about 12k down (I think the cut off for my speaker is about 8k from memory) to 1.8k.

I tried all sorts of filters and stages but found the most natural sounding was the very basic 1 r + 1 c design followed by a gain stage.

Cheers Shaun

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