KVR Audio

SteffenPL · Post by **SteffenPL** » Tue Feb 02, 2021 6:04 pm

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.)

thecontrolcentre · Post by **thecontrolcentre** » Tue Feb 02, 2021 6:09 pm

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

BertKoor · Post by **BertKoor** » Tue Feb 02, 2021 6:21 pm

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?

SteffenPL · Post by **SteffenPL** » Tue Feb 02, 2021 7:30 pm

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.

IMG_1582.JPG

nix808 · Post by **nix808** » Tue Feb 02, 2021 8:10 pm

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

hope it works nicely for u!

SteffenPL · Post by **SteffenPL** » Tue Feb 02, 2021 8:31 pm

Thanks!

I will come back when I want to do other filters

Hopefully knowing a bit more then

BertKoor · Post by **BertKoor** » Tue Feb 02, 2021 9:11 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)

SteffenPL · Post by **SteffenPL** » Tue Feb 02, 2021 10:06 pm

I see. Thanks for the hint.

BertKoor · Post by **BertKoor** » Wed Feb 03, 2021 7:39 am

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.

SteffenPL · Post by **SteffenPL** » Wed Feb 03, 2021 10:38 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.)

SteffenPL · Post by **SteffenPL** » Sun May 16, 2021 8:05 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

BertKoor · Post by **BertKoor** » Sun May 16, 2021 9:30 am

It's fun indeed.
Thanks for sharing!

Dasheesh · Post by **Dasheesh** » Sun May 16, 2021 10:07 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 · Post by **xtp** » Sun May 16, 2021 10:39 pm

SteffenPL wrote: ↑Sun May 16, 2021 8:05 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

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