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Forums     Plugins     Impulse Modeler and Deconvolver Deconvolver help -> dc IR does not match the source / optimal sweep length


Dear Aleksey,

i am interested in the Voxengo Deconvolver but i have some questions before purchasing:

I ran the Trial but my test-results were not pleasing yet.  Maybe i am doing something wrong.  Well, i am just a musician with limited technical knowledge so I would be glad for some tipps:

My aim is to create specific IRs (EQ-Curve and Cab) to import into a Fractal Audio Axe-FX Hardware Unit.  The deconvoluted files have to be mono, 48Khz, 24 Bit, 1024 Samples.

As an easy starting point i wanted to create IRs of 3 different VST Plugins within my DAW (48Khz and 24 bit)

(a: EQ, b: Reverb, c: Cab-Simulation):

1) created a 6s long Sweep with fades using the Voxengo Deconvolver

2) imported the file into the DAW and added a VST Plugin

3) reduced the Audio-level of the sweep to receive a nearly -0.3 db wet output Level (after VST FX)

4) set the Left marker at the beginning of the Sweep-file and right marker at the end of the sweep +1 sec

5) exported the 100%-wet Signal (length 7 seconds) mono, 24bit, 48Khz

6) deconvoluted with the Voxengo using REVERSED Technique

7) duplicated the original Sweep within my DAW to a second Track and added the SIR2 (even tried Waves IR1)

8) imported the dc-File into SIR2 and compared the output signal of both tracks

=> I thought both tracks should now be nearly identical (Track 1: Sweep + VST; Track 2: Sweep + SIR2 with imported dc-IR)

9) compared the signals acoustically and with some Audioanalyzer and there a big differences in the signals

a) the dc-file of the VST-EQ was nearly inverted and the highs were cutoff, the ir was completely unusable

b) the Reverb was less loud and the predelay was slightly different but it worked okay, i would say 85% match.

Maybe i am doing something wrong, i would be glad for any tipps.

My last question is about sweep-file length.  My final IRs should be max 1024 Samples (21,33 ms).

So what would be the best value for the Voxengo deconvolver to setup the sweep file?  0.02 s with fades, ore am i on the wrong way?  Would be glad for any tipps.

Thank You very much.

cheers - Nick


Your routine seems correct, but I would suggest you to add 1s of pre-silence as well as 1s of post-slience you've added already.  If the VST EQ/VST FX is non-linear the deconvolution will fail - it works with linear filtering only.

The 6s sweep is fine.  But you will have to chop-off the resulting IR file to 1024 samples - this may affect the sonic quality, of course.

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