constant q transform

Discussion in 'Building With Reaktor' started by ANDREW221231, Sep 14, 2017.

  1. ANDREW221231

    ANDREW221231 NI Product Owner

    okay, i cannot actually say this a constant q transform. more honestly it is a slapdash reaktor structure with the core elements of a constant q transform taken 'into consideration'. from the schlumpy phase delay increasing at low frequencies and the strange attenuation of high frequencies, it seems there is more to be desired towards a constant q factor, whatever that actually means in relation to reaktor's R.

    however, the general idea is preserved and what you have is a 200 voice pseudo fourier transform with the bins spaced logarithmically according to pitch instead of frequency. to make this work requires logarithmic bin sampling (cough), making the end result related to or even equivalent to methods producing the wavelet transform.

    it doesn't admittedly sound that good, and decidedly the most interesting thing about it is when its hooked up backwards. the basic flow is multivoice bandpass with additional allpass to achieve quadrature for sine bank resynthesis output. when this is added instead of subtracted, it is equivalent to the phase being backwards. okay, fine, but if we switch to linear sampling of the output instead, it spreads the frequencies out in all directions. it the quadrature is at this time also switched to addition, the frequencies are sucked back into presumably what one would expect from a 200 bin fourier transport with the phase unplugged: quantized into multiples of the lowest frequency.

    the curious bit for me was how it was arbitrarily changing the frequency of the individual sine frequencies despite leaving the actual tuning of the oscillators untouched, which seems like some kind of amplitude modulation but without sidebands?? anyway its something to do with summing/cancellation because it doesn't still happen so cleanly with an isolated voice. but still, it had me pretty damn interested trying to make heads or tails!

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    Last edited: Sep 16, 2017