TOPIC: DDRC-88A for Dirac and FIR linear phase crossover?

Question on DDRC-88A:

Can it support Dirac Live along with FIR linear phase 3-way crossover?

My friend is using a Behringer DCX2496 for 2-way crossover with time alignment (between KEF LS50 & stereo subwoofers: bi-amped configuration), and would like to add room correction into his setup and may also upgrade his speakers to 2-way + stereo subs (tri-amp configuration: 3-way crossover), so would like to understand whether DDRC-88A can implement FIR linear phase crossovers in conjunction with Dirac Live.

Yes it can , I’m doing something similar

Nothing wrong with giving Dirac a helping hand for efficiency, just measure a bunch of averages and make sure your fir is indeed closer to a linear response vs an iir. Acoustics are freaky and just because you hit the fir function doesn’t always mean better.


Dirac will make Left and Right resemble each other more than it will try to be close to the “0”deg phase in magnitude. Dirac will still leave (or make) phase wraps if it means a more symmetrical phase response compared to the opposite channel. It does a good job within its power ability and optimization is good.
All that means is you might spend a bunch of time making linear phase crossovers and it might just undo what you did on that output (88) to make all the channels resemble one another.

If you listen spot if center of the drivers there will most likely be less and less of a concern for it making it worse as L&R should be mostly symmetrical because of equal path lengths.

So the short answer , again is yes it can work great, just measure and see what’s happening before and after .


Andrew

Thanks, Andrew!

In reading the DDRC-88A manual and looking at the DDRC-88BM plug-in, I don't see any provision for direct FIR filter imports, similar to the ones in the OpenDRC series or the miniDSP 2x4 HD. Dirac Live is clearly in the processing path, but FIR blocks are not.

I'm interested in getting linear phase crossover & EQ done for active 2-way speakers (or speaker/subwoofer combos) with FIR filters before moving on to room correction. Can you elaborate a bit on how all this can be achieved with DDRC-88A? Many thanks!

Sorry scan80269


I misunderstood, I thought you said a dcx2496 in there somewhere, no the 88 can not access fir. Dirac Live does all of that:

I understand the 88 is meant for 8 full range outputs and not multiway, but it should sill make your IIR linear , just drag the curtain to somewhere around your xo or for best results and keeping boosts managed outside the correction and or draw out the first octave in the target as the first few dB of crossover. That’s the only way I can think of to manipulate the 88 to act as linear phase multiway box. If you drew out 10db of crossover slope in the target , than engaged the built in crossover after that and pulled the curtain over so Dirac doesn’t add stupid amounts of stop band boost.

Or , use the ddrc22d upstream of a few fir banks external, that’s what I am doing, and like it quite a bit


Andrew


scan80269 wrote:

Thanks again, Andrew!

I have come to the same conclusion that the miniDSP boxes supporting Dirac Live don't support FIR filter imports, so if my friend wants both Dirac Live and FIR linear phase filters he will need to cascade two boxes, with the Dirac Live box upstream from the box doing the FIR filters.

I also discovered that FIR filters may not be the best for low frequency EQ adjustments. Parametric style EQ especially with high Q settings at low frequencies (e.g. subwoofer range) appear to require a large number of FIR taps that can easily exceed the limits imposed by the miniDSP boxes, and also result in large latencies. So it seems FIR filters for linearizing phase can be done down to about 200-300Hz, but in the bass range, PEQ with IIR filters is much more practical.

My friend ended up with a DDRC-22A upstream from a 2x4HD.

DDRC-22A provides Dirac Live room correction and 2x4HD implements FIR linear-phase crossover filters. He is quite happy with the results.

We're looking for more 96K FIR taps to work with in the 2x4 HD. PEQ, crossover & compression features are not used, and only the FIR feature is used for doing the linear-phase crossover filters. A plug-in that exposes only matrix, gains, delay & FIR (tap count maximized) for the 2x4 HD would be ideal.

@scan80269

In answer to your question:
- the DDRC-88A doesn't provide FIR access. It won't be possible to ever do as Dirac is already taking a LOT of resources.
- Crossovers/comp take very little resources. In a 2x4HD plugin, 75% is being used by FIR taps. The remaining is for the basic operation.

DevTeam

Got it! Thank you.

I suppose one brute-force way to get more 96K FIR taps is to use two 2x4 HD boxes, one for each channel. Using just one input and two outputs of each 2x4 HD, the FIR tap count should max out at 2042 for each of the two used outputs.

Currently, my friend uses a 1280- tap HPF for his speakers and 768-tap LPF for his stereo subwoofers, with a single 2x4 HD. A delay is set to compensate for the FIR count difference between HPF & LPF as well as for time alignment. With a sub crossover frequency set at 200Hz (Linkwitz-Riley 4th order, 24dB/oct), the HPF deviates from ideal response significantly at the bass frequencies, so using two 2x4 HD to get the tap count up to 2042 should help here.

Ideally, the 4084 tap count available for the two used output channels of a 2x4 HD can be divided into something like 3072 (HPF) and 1012 (LPF), but the 2x4 HD plug-in imposes an upper limit of 2048 taps per channel.

You could try just using an IIR for the 200 Hz crossover as in theory Dirac Live will "linearize" it anyway - it would be interesting to see a measurement/comparison.