Rear Filling with C-DSP - Car Audio | DiyMobileAudio.com | Car Stereo Forum

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Old 3 Days Ago   #1
 
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Default Rear Filling with C-DSP

Has anyone played around with getting a decent Rear Fill setup with just a C-DSP?

I've done a fair bit of searching, most of the discussion revolves around the Helix.

as far as i can tell, the C-DSP only does channel summing, so all I can get is L+R and the inverse of that.

so at best it seems all I can do is sum the channels together to get a mono signal, and bandpass it appropriately and delay it either max (15ms or so) or delay it so the stage is centre of the vehicle.

The only other option I have noticed is daisy chaining a 2x4 miniDSP off the outputs of the C-DSP(or any other DSP for that matter) and using the Rear Fill Plugin they have.

has anyone managed to achieve something decent with just the C-DSP?
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Default Re: Rear Filling with C-DSP

I'm using a 2x4 with mine since I had it laying around. Diyma user Zippy is getting good results with his 360.3 and he said delay on it is less than the c-dsp. The way he explained it to me was he fades all the way to the left and delays the left rear until the left side raises up with good space and then repeats for the right. Don't think he's channel summing or anything. I'd send him a pm and ask him directly though if he doesn't see this thread.

In your case, I'd try it the way Zippy explained it to me (he did a good job with it because I've heard his work with my own ears). And then sum L-R with the negatives of the rears twisted together and each positive connected to the amp and see how that works out with just 15ms of delay. The idea is to simulate reflections that you'd normally get in a really big venue. This usually requires over 20ms of delay. I'm at 24.58ms with my rears.

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Old 3 Days Ago   #3
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Default Re: Rear Filling with C-DSP

The C-DSP allows manual entry of filter coefficients for the input section, right? I saw someone explain this once and it seemed brilliant.

Essentially you invert the polarity of the right channel on the *input* side of the C-DSP. Then you also invert the polarity of all the *output* channels for your right side speakers (sub, midbass, midrange, tweeter). That should give you a net of no change and everything should sound exactly as it did before.

Then you sum the left input channel with the right input channel and assign it to output 1 (or whatever channel you want). Then output 1 will be an L-R signal which is what you want for surround, and you feed that to both of your rear speakers with a y-splitter cable to send the signal to the amplifier. You can go one step further and wire the right rear surround speaker with opposite polarity from the left rear surround speaker so that the "surround" channels are out of phase with eachother too by flipping the + and - wires on the amplifier terminal.

To invert the phase of the right input channel, you need to use the advanced IIR filters section (might be labeled as biquad) and change one of the coefficients from "1" to "-1". I am pretty sure it is the B0 coefficient you want to change, I think.

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Default Re: Rear Filling with C-DSP

Quote:
Originally Posted by Jazzi View Post
The C-DSP allows manual entry of filter coefficients for the input section, right? I saw someone explain this once and it seemed brilliant.

Essentially you invert the polarity of the right channel on the *input* side of the C-DSP. Then you also invert the polarity of all the *output* channels for your right side speakers (sub, midbass, midrange, tweeter). That should give you a net of no change and everything should sound exactly as it did before.

Then you sum the left input channel with the right input channel and assign it to output 1 (or whatever channel you want). Then output 1 will be an L-R signal which is what you want for surround, and you feed that to both of your rear speakers with a y-splitter cable to send the signal to the amplifier. You can go one step further and wire the right rear surround speaker with opposite polarity from the left rear surround speaker so that the "surround" channels are out of phase with eachother too by flipping the + and - wires on the amplifier terminal.

To invert the phase of the right input channel, you need to use the advanced IIR filters section (might be labeled as biquad) and change one of the coefficients from "1" to "-1". I am pretty sure it is the B0 coefficient you want to change, I think.
correct you can input the filter coeffs manually on both sides, input and output.
I'll chase up with minidsp and or google as to how I go about inverting the biquad(as in which coeff to invert).

I won't be able to achieve more than 15ms delay, but it's better than nothing at this moment in time.
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