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Using Linkwitz Riley filters
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November 26, 2016
1:13 am
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Niro
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September 23, 2015
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Hi Will,
I use two Linkwitz Riley filters (one LPF and one HPF).
When I placed both filters in parallel with the same cutoff frequency, output isn't same as without filters.
Frequency response is similar, but amplitude is bigger (+ 2dB).
I don't forget multiply one band by -1.0;
Is it correct behaviour?

Thanks for reply

December 3, 2016
1:09 am
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W Pirkle
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January 28, 2017
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No, you should get a perfectly flat response.

You can test this with the SpectralDynamics project code. Just change the processAudioFrame( ) code that creates the LF and HF outputs (here I'm commenting out the original code):

// create left and right LF outputs
//float fLFOutputL = fGn*fLeft_LF_Out*fLFOutputGain;
//float fLFOutputR = fGn*fRight_LF_Out*fLFOutputGain;

float fLFOutputL = fLeft_LF_Out;
float fLFOutputR = fRight_LF_Out;

... then later

// create left and right HF outputs
//float fHFOutputL = fGn*fLeft_HF_Out*fHFOutputGain;
//float fHFOutputR = fGn*fRight_HF_Out*fHFOutputGain;

float fHFOutputL = fLeft_HF_Out;
float fHFOutputR = fRight_HF_Out;

Then, compile and test the frequency response - it will be a flat line at 0.0dB.

- Will

March 9, 2017
8:43 am
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Niro
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Thanks for your answer.
I have tried the Spectral Dynamic project and the frequency response is perfectly flat.
However the output signal is louder than input signal (about 2dB).
How is it possible?
Thank you

March 9, 2017
10:29 am
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W Pirkle
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I am not seeing this.

Using the Spectral Dynamics project, in COMP mode - set Thresholds to 0dB, set Ratios to 1.0 so that no processing goes on (alternatively you could modify the project omit the gain computer and fix it at 1.0), set both output gains to 0.0dB, sensitivity controls all at 0.0

1) test frequency response with analyzer: flat at 0dB - the Frequency Response test does not normalize anything so what you see is what you get

2) use oscillator in RackAFX, set to 0dBFS, any frequency produces same output in both oscilloscope, FFT analyzer, and RackAFX VU meters, which are calibrated to 0.0dBFS

3) use a test .wav file, 1kHz @ -3dB (in case there is gain), then use Audio/MIDI -> Process Into WAV File, produces WAV file with identical output amplitude waveform (-3dB).

4) moving the fc (splitting frequency) does not change anything

March 9, 2017
2:20 pm
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Niro
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Thanks for tips.

I did a few experiments with project Spectral Dynamic from your web, but with same result.

Frequency response is flat at 0 dB and in RackAFX everything seems allright.

However if I load wav files (sine 1kHz and white noise) and than I process into output wav file (with various settings of corner frequency) amplitude is higher than original (the increase is in the range 0.5-1.5 dB in addiction on corner frequency).

I made Spectral Dynamic as VST plugin and it has exactly the same behaviour.

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