Alex Weiss wrote:

> I was wondering if somebody here has ever created an exciter with csound.
> It's one of the few audio engineering things that I've never really
> understood and where only little literature exists. I know technically an
> exciter just distorts a signal, but it does it in a very specific way that
> I've never been able to recreate. Obviously, the standard distortion
> opcodes don't cut it. And if i sit down with a piece of paper and a pen and
> do some math, I can only come up with methods that create a significant
> amount of non-harmonic material as well, which, as I understand, an exciter
> doesn't. So, does anybody have experience with that?

I've never seen a instrument that does this, but an exciter should be relatively
easy to recreate. An exciter is takes the original signal, high pass filters 
it, distorts this high pass signal and then adds it back into the original
signal.

The above would be relatively trivial in analog electronics. When doing it
digitally, you need to be aware of aliasing. Whenever you introduce harmonic
distortion in the digital domain you need to make sure the the resultant
harmonics don't end up higher than half the sampling rate.

If I was wanting to emulate an exciter, I would do it by upsampling before
and downsampling after the distortion.

Erik

Alex Weiss wrote:

> Hm. Maybe I'm doing it wrong, but I don't think I've ever heard a
> pleasant-sounding distortion algorithm (by "pleasant" I mean the way an
> exciter would sound). Everything just sounds... well, distorted, for lack
> of a better word. Like clipping. Even when I only add a tiny amount.

I would suggest you try the mathematics function tanh() which gives a
relatively soft clipping.

Erik

Alex Weiss wrote:

> Thanks, Eric. You mentioned something I've always been curious about: What
> determines if a waveshaping function produces only odd (or only even, for
> that matter) harmonics? I.e., what properties does a waveshaping function
> have to have in order to only produce odd harmonics?

If you look at the tanh function here:

    http://www.mathworks.com.au/help/techdoc/ref/tanh.html

you will see that, for all x, f (x) == -1 * f (-x) which makes tanh an
'odd' function (see [0]) and will produce only odd harmonics. And even
function like f= x * x, will produce only even harmonics. 

There are also functions that have a mixture of odd and even features
and therefore produce a mixture of odd and even harmonics.

HTH,
Erik


[0] https://en.wikipedia.org/wiki/Even_and_odd_functions

On Jan 8, 2012, at 11:15 AM, Erik de Castro Lopo wrote:

> Alex Weiss wrote:
> 
>> Thanks, Eric. You mentioned something I've always been curious about: What
>> determines if a waveshaping function produces only odd (or only even, for
>> that matter) harmonics? I.e., what properties does a waveshaping function
>> have to have in order to only produce odd harmonics?
> 
> If you look at the tanh function here:
> 
>    http://www.mathworks.com.au/help/techdoc/ref/tanh.html
> 
> you will see that, for all x, f (x) == -1 * f (-x) which makes tanh an
> 'odd' function (see [0]) and will produce only odd harmonics. And even
> function like f= x * x, will produce only even harmonics. 
> 
> There are also functions that have a mixture of odd and even features
> and therefore produce a mixture of odd and even harmonics.
> 
> HTH,
> Erik
> 
> 
> [0] https://en.wikipedia.org/wiki/Even_and_odd_functions
> 
> -- 
> ----------------------------------------------------------------------
> Erik de Castro Lopo
> http://www.mega-nerd.com/
> 
Very, very moons ago, I wrote a simple plugin for linux snd, which worked like described,  Hi-pass filter and clipping the signal and mixing with the original. I had some parameters to control the process, and used it for some old cassettes, still have Genesis' Harold the Barrel as mp3 in iTunes, and it sounds quite good.

Incidentally just started to write the thing with jVSTwRapper for Wavelab Elements 7 on OSX. Java is surprisingly fast to do audio processing, a wavelet denoiser works in real-time, even as stereo and 2048 sampleFrames.

best,

-matti




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