Dirac & group delay

[Narukama]

Hi all, please bear with me because I will describe my system first before go to my question.

 

I plan to try Dirac as my DRC. I use win 8 and JRiver 19 as a player outputting 2.0 channels since my DAC ionly accept 2. 0 channels input and outputting 2. 0 as well.

 

My set up is pretty simple. Laptop - USB - 2ch DAC - unbalanced RCA - integrated amplifier (with LR outputs) - the mains speakers has passive XO and connected by speaker wires from speaker terminals in the integrated.

 

However for my stereo subwoofers the chain is a little different : preamp LR output - Behringer DCX2496 (active crossover with stereo subwoofers output) - powered subwoofers. Again the Behringer would be used srictly as an active XO for strereo subwoofers only. It won't have any connection to my mains at all. I want to run my mains "full range" without HPF and let their natural drop off naturally.

 

My concern is the Behringer's latency. I don't know the exact number yet but expect to get reply from Behringer soon. But that's kind of not the main point. My point is if the latency too high that I have to move the subs closer to my sitting area, I can't do that without involving a divorce lawyerr LOL.

 

Here is the main question, assuming the Behringer's latency is 5ms and I cross the LPF at 120Hz/24db, would I be able to apply 5ms delay for frequency above 120Hz (hopefully I could set the slope to 24db also) using Dirac to compensate the delay caused by Behringer? Or perhaps JRiver could do that as well? Assuming eiter Dirac or JRiver could do group delay but not be able to set the slope below 120Hz) Am I correct to say hat means all my speakers are time alligned,? What will happen on the over lap freq around 120Hz? My mains are small ported monitors which roll off around 100Hz with 24db slope.

So there is a considerably huge 20Hz gap between 100-120Hz and some freq bellow and above those points (the over lap freq down slope). So I imagine if my subs are delayed because the latency from the Behringer while my mains are not delayed I don't think I would get good sound.

 

Am I correct to expect that the sound near the XO LPF point would be bad? Would anyone kindly explain in layman terms how the sound will be affected. Such as the sound near that freq would has "echo" or maybe they would out of phase and produce cancelation or that group delay would create deep null/peak in my freq response, etc?

And again could DIRAC solves my problem?

 

Note: I apologize for my writing errors and wrong technical terms. Feel free to correct me. My native language is Indonesian and I'm very new in home audio / HT hobby also don't have EE knowledge at all.

 

Cheers,

Thomas Narukama

[flak]

Hello Thomas,

 

if I understood you correctly you do'nt want to use the Behr for hi-pass crossovering to your main speakers and you want to avail of a 24 dB/octave roll off at 100 Hz of your speakers (I imagine because of transparency and AD/DA conversion issues).

My personal opinion is that the DCX2496 is better than what generally thought but that's another story, may I ask you what refrains you from crossing the subwoofer at 100 Hz instead of 120 Hz (provided that really is the ideal XO frequency)?

Are you going from the preamp to both the power section of the integrated amplifier and the digital crossover for the powered subwoofer?

 

Ciao, Flavio

[Narukama]

Actually I plan to cross my subs at 120Hz/24db & 50Hz/24db. It doesn't mean L sub crossed at 120Hz and the right at 50Hz. They would be crossed at the same point depends on the material source for example those subs will be operated in stereo at 50Hz for music playback. But those same subs will also be used in mono in 5.2 configuration when I watch movies. My subs both are SVS SB13-ULTRA. I required 2 different LPF because I use different LR speakers. For music I use a pair of Dynaudio Confidence C1 Signature and for movie I use 5 Paradigm MilleniaOne speakers.

So I plan to bypass the internal SB13's XO, EQ, etc and perhaps will only adjust polarity if needed. If I don't bypass the SB13's XO then I have to set the XO at 50Hz for music. For movie I could set the XO at 120Hz using my AVR. But that means everytime I switch the sources I have to manually turn the SB13's XO on for musicc & off for movie. I am too lazy to do that and it's dangerous because my 11 y.o. kid would also use my audio/HT system.

So that is the whole reason why I need one external XO with stereo subs output or two XO with one sub output.

 

I didn't tell the whole story because it would be a very long letter & my main objective is only to know whether Dirac could be used to delay a certain freq range (group delay?) to compensate/time align my subs and mains (if the external XO and SB13's DSP cause high latency). This information will also be useful if in the future I use wireless transmitter and receiver and I know at least one device that has 27ms latency! Convert that to ft and you can imagine what my room would look like.

 

To answer your question why I don't want to high pass my mains through Berh, there are 2 reasons:

1. most of my music files are 24/96-192 and quite many DSD which goes to a DSD PCM DAC which sound I really love. Going through Berh means another AD-DC conversion process which also down sampled any music beyond 96Hz. As good as Berh ADC-DAC is, I doubt it would sound anywhere near my current DSD PCM DAC. So you're right, I don't want to sacrife the sound from my Dyn C1. I Don't mind to compromise the bass sound quality from the subs though. I believe my ears couldn't tell the difference anyway.

2. It should be obvious by now that I use 2 different type of speakers.

 

Anyone has any idea how to time aligned my subs and LR mains speakers? I prefer to do it in my comp by using a software, plug in or whatever else because I want to preserve the sound quality produce by my DAC and Integrated amp.

 

Thanks for reading this long letter.

 

Cheers,

Narukama

[beanbag]

I was just reading about how time alignment wasn't possible when using a USB microphone, such as the Umik-1, due to no loopback. What does that mean for the impulse correcting features of Dirac?

[dallasjustice]

I was just reading about how time alignment wasn't possible when using a USB microphone, such as the Umik-1, due to no loopback. What does that mean for the impulse correcting features of Dirac?

 

DIRAC does correct for time domain errors even with a USB mic. Loopback or synchronous measurement isn't needed provided DIRAC only has to compensate for one clock drift.

 

If you use subs with DIRAC, it's really best to get the time delay and crossover/phase correct first. With regard to 2.2 or 2.1 stereo music playback, DIRAC isn't going to know you are using subs this way and will only "see" a 2CH system because the sweeps are only 2CH. You can use subs with DIRAC full version. However, full version seems to be limited to home theater set up with LFE subs. It doesn't do crossover.

 

If you want 2.1, 2.2, 2.3 or 2.4, you need to dial in the correct delay and crossover down stream first. Once you have your main R/L delays and rear sub delay correct (if needed), get your crossover set with a smooth phase trace. There's no "easy button" for this. It takes some knowledge of REW. Lastly, run a DIRAC sweep as long as the subs, crossover and delay all happen in the chain AFTER the DIRAC filter.

 

Michael.

[flak]

Hello Thomas,

 

yes, Dirac Live will align the subwoofer (you have downstream crossovering) and you can check the results when looking at the impulse response in the DLCT.

The absolute maximum limit is 10 milliseconds so it should satisfy your requirements but as you know you can anyhow test the results by downloading the free demo.

 

Ciao, Flavio

[flak]

Hello Beanbag,

 

as Michael has just explained Dirac Live does not have a clock problem as it takes an additional measurement (three instead of two) to account for clock drift between input and output, this allows to use a USB microphone and the DAC of your choice instead of having to necessarily use an audio card because of clock issues.

 

Ciao, Flavio

[dallasjustice]

Flavio,

That's interesting that it can correct up to 10ms. That's pretty good. In my case, I need about 18.5ms to delay my main R/L to get my frontwall sub to time align.

 

Hello Thomas,

 

yes, Dirac Live will align the subwoofer (you have downstream crossovering) and you can check the results when looking at the impulse response in the DLCT.

The absolute maximum limit is 10 milliseconds so it should satisfy your requirements but as you know you can anyhow test the results by downloading the free demo.

 

Ciao, Flavio

[beanbag]

If you want 2.1, 2.2, 2.3 or 2.4, you need to dial in the correct delay and crossover down stream first. Once you have your main R/L delays and rear sub delay correct (if needed), get your crossover set with a smooth phase trace.

 

How does one get a "correct delay" and "smooth phase trace"?

[dallasjustice]

How does one get a "correct delay" and "smooth phase trace"?

That's above my pay grade. I had Nyal do it for me. Here is a good thread just to give you a taste of how many different ways it can be done:

Case Study: Sub Alignment using REW v5 - Home Theater Forum and Systems - HomeTheaterShack.com

[kjbii]

Hi Michael,

 

I'm still digging through your old posts. Did you decide to abandon this alternative? Is Dirac an option, for delay and crossover alignment?

 

thanks, Ken

 

 

DIRAC does correct for time domain errors even with a USB mic. Loopback or synchronous measurement isn't needed provided DIRAC only has to compensate for one clock drift.

 

If you use subs with DIRAC, it's really best to get the time delay and crossover/phase correct first. With regard to 2.2 or 2.1 stereo music playback, DIRAC isn't going to know you are using subs this way and will only "see" a 2CH system because the sweeps are only 2CH. You can use subs with DIRAC full version. However, full version seems to be limited to home theater set up with LFE subs. It doesn't do crossover.

 

If you want 2.1, 2.2, 2.3 or 2.4, you need to dial in the correct delay and crossover down stream first. Once you have your main R/L delays and rear sub delay correct (if needed), get your crossover set with a smooth phase trace. There's no "easy button" for this. It takes some knowledge of REW. Lastly, run a DIRAC sweep as long as the subs, crossover and delay all happen in the chain AFTER the DIRAC filter.

 

Michael.