spectrumdata info

[benHc]

Hi there!

I'm developping a VIS plugin for winamp 5.x
i'm trying to analyze the spectrum data
given by winamp to split the frequencies
into bass,medium and treble (or more)
I have a few question:
1) what range frequencies do represents the spectrumData?
60 hz to 16 000 hz? where can i get this info?
2) the spectrumData scale seems to be linear. i suppose it's more easy to work with a logarithmic scale. How do i convert the spectrumData to my own arrayData with a logarithmic scale?

Thanks you!

[eleet-2k2]

Hi benHc.

The human hearing range is from 20Hz to 20kHz, so would it not make sense for the spectral data to be in the same range?

Also, if you want a breakdown of the frequency ranges, I'd say this is how they breakdown (but this is imho and I'm not a sound expert )
Bass: 20Hz - 600 Hz
Midrange: 600 Hz - 12 kHz
Treble: 12 kHz - 20 kHz

[misterkik]

if i understand well, there are just a few values for the bass and a lot more for the medium and the treble ? is there a possibility to aquier ther same number of value for the bass, medum and treble ?

tkx,

Kik

[eleet-2k2]

Well you're talking about the Winamp equalizer. The thing about an equalizer can have as many or as few bands of frequencies to control it. For exaple, there are some professional equalizers that have 20+ bands, while Winamp's EQ has 10 bands + preamp.

The bass, midrage and treble frequencies are actually ranges of frequencies (called bands) that vary from 20 Hz - 20kHz (the human hearing range) and so each section of bass, midrange and treble are just smaller ranges within our hearing threshhold.

[misterkik]

OK.
In fact i m doing a vis plugin. I want some objects moving in accordance of the bass, the mid and the treble. I don t exactly understand how to treat the data from the spectrum data (given by winamp). When I use these spectrum data, the results are not in accordance of the music.

My question is how to tell winamp to give me some values which could represents the differnts bands of frequencies.
Do I use the spectrum data or anything else ?

Thx.

Mister KIK

PS: thx for your explainations eleet-2k2.

[tracerh]

you can get hold of the avs and geiss code(or two of the vixs plugins anyway) somwhere around here, maybe in the vault

[tracerh]

Look, this is in the bloody SDK

code:
for (x = 0; x < 288; x ++)

{

MoveToEx(memDC,x,(y*256+256)>>(this_mod->nCh-1),NULL);

LineTo(memDC,x,(y*256 + 256 - this_mod->spectrumData[y][x])>>(this_mod->nCh-1));

}

If you don't know about spectrum analysis, fft's and lovely stuff like that already. You'd better be prepared to take a hardcore crash course ... or rip off someone elses code

[tracerh]

gforce and whitecap you can get the src for

[misterkik]

Tkx very much I ll take a look at that

Mister KIK

[FabioF68]

As for any FFT operation, the scale is linear with frequency, as the sampling is made in constant steps with frequency. The information retained by the spectrum data is complete (reversing the FFT you can reconstruct the original signal).

The issue is only a visualisation one, as we have to span 3 orders of magnitude in frequency (20-20K Hz), hence a log-scale is the one commonly used. A proper algorithm is needed to transform the evenly spaced frequency samples to the log-scale on the screen, accounting for the undersampling at low frequencies and oversampling at high ones.

I'm trying to write one of my own, but if someone is aware of something already working... he's welcome!

bye
Fabio