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JBL M2 crossover with the openDRC 6 years 4 months ago #26894

  • iansr
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For splitting the signal for the two (and up to three) opendrc DI or DA I suggest the behringer src 2496 (see www.music-group.com/Categories/Behringer...aces/SRC2496/p/P0141). Although it is not very chic, it brings high value to the boxes:
Analog input ADC with +20db, 96kHz or alternatively digital input up to 192kHz SRC which is better than the SRC of the opendrc, particularly if the digital signal is not excellent. Then there are 3 digital outputs which are absolutely synchronized to 96kHz,24dB which provides a very clean signal for the opendrc and improves their "musical timing". Under 100€ on ebay auctions.

Before, I tried the passive TOSlink splitter which degraded the optical signal severly. I also tried the best active Marmite TOS-splitter 1 to 4, 192kHz which cleaned and amplified the signal a bit, but there were glitches every minute due to digital synchronizing problems.


I've looked at this and it has one XLR output, one RCA output and one toslink output. So you don't get 2 similar outputs.

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JBL M2 crossover with the openDRC 6 years 3 months ago #26915

  • planetti
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:huh: Sorry, but
1xSPDIF-RCA + 1x SPDIF-TOS + 1xDI-XLR = 3 digital outputs, and all are simultaneously active and they exacly correspond to the 3 digital inputs of the OpenDRC DI or DA. :woohoo:

Of course they are not similar but you can use all 3 perfectly synchronized based on a reliable internal clock. Isn't that perfect for our use?

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JBL M2 crossover with the openDRC 6 years 3 months ago #26916

  • pos
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I did not experiment audible problems with the toslink splitter.
I might be completely wrong here, but I prefer to have a completely passive device rather than yet another ASRC in the signal chain.

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JBL M2 crossover with the openDRC 6 years 3 months ago #26919

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I've read that provided your splitter maintains impedance then the only potential issue with a passive splitter is if halving the strength of the signal prevents the receiving device (the DI in this case) from locking on to the signal.
It sounds like you've not had that problem Thomas.

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JBL M2 crossover with the openDRC 6 years 3 months ago #26929

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Hi POS,
you are basically right, but I had a problem:
My sound material is on 44.1 kHz, my audio cocktail X10 has one toslink output. After I made exhaustive sound checks with (the same) sound material on 96kHz, 48kHz and 44.1kHz I realised a noticeable difference: on 48kHz and even more on 96kHz the "timing" was more precise. But the passive optical y-splitter weakened the signal such that there were dropouts, even with good cables. Then I tried 4 different active toslink-splitters, whereby not even the best one was able to synchronise to the signal by producing glitches every minute.

The ultramatch pro SRC2496 was the solution:
It has a very tolerant SRC, uses an accurate upsampling algorithm to 96kHz and provides reclocking by a good internal clock, so you get stable and jitter-free signals on 96kHz/24dB, which the openDRC boxes process to their 48kHz without introducing any time imprecision. You can hear the differences when you switch the output frequencies to 32/44.1/48/88.2/96 kHz on the ultramatch. The 96kHz produces the best result because the instruments are more "stable", the rhythm is more "precise" and the sound stage is "deeper".
And you also get a noisefree ADC and a reasonable headphone output. One maybe additionally buy the wooden side plates instead of the original ugly side clamps.

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JBL M2 crossover with the openDRC 6 years 3 months ago #26930

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Hi POS,
you are basically right, but I had a problem:
My sound material is on 44.1 kHz, my audio cocktail X10 has one toslink output. After I made exhaustive sound checks with (the same) sound material on 96kHz, 48kHz and 44.1kHz I realised a noticeable difference: on 48kHz and even more on 96kHz the "timing" was more precise. But the passive optical y-splitter weakened the signal such that there were dropouts, even with good cables. Then I tried 4 different active toslink-splitters, whereby not even the best one was able to synchronise to the signal by producing glitches every minute.

The ultramatch pro SRC2496 was the solution:
It has a very tolerant SRC, uses an accurate upsampling algorithm to 96kHz and provides reclocking by a good internal clock, so you get stable and jitter-free signals on 96kHz/24dB, which the openDRC boxes process to their 48kHz without introducing any time imprecision. You can hear the differences when you switch the output frequencies to 32/44.1/48/88.2/96 kHz on the ultramatch. The 96kHz produces the best result because the instruments are more "stable", the rhythm is more "precise" and the sound stage is "deeper".
And you also get a noisefree ADC and a reasonable headphone output. One maybe additionally buy the wooden side plates instead of the original ugly side clamps.


I guess if you also have a turntable (which I do ) then the ADC function will be useful as presumably you would just switch the input selector to the analog inputs and you'll still get your 2 digital outputs?
It's a shame to have to do the ADC but that's the price you pay for having a DSP crossover.

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JBL M2 crossover with the openDRC 6 years 1 month ago #28396

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rePhase is indeed behind it and you can find rephase presets in the google document linked in the first post.
But the rePhase correction is only minimum-phase for now, replicating the original M2 settings.
I plan to add phase linearisation as soon as I get a chance to precisely measure its behavior.

To me the openDRC (one per loudspeaker) is the perfect platform for applying these settings in pure FIR, be it minimum-phase or not.

THomas,
I'm not sure how close your current FIR settings are to being phase-linear (?), but after reading some acrticles recently by advocates of the importance of phase linearity I was just wondering whether you still intend to revise your settings at some point?

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JBL M2 crossover with the openDRC 6 years 1 month ago #28483

  • pos
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Hello Ian,

Turning the M2 into a minimum-phase device (ie linearizing the phase of the crossover) is pretty straightforward as the acoustical crossover is a text book 36dB/oct LR at 750Hz, pretty much.
Turning it into a fully linear-phase device requires you to also linearize the BR at around 25Hz.

Of course both modifications require a little bit more taps than the original minimum-phase settings, and an additional delay (~50ms for a fully linear-phase system).
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JBL M2 crossover with the openDRC 6 years 1 month ago #28506

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Hello Ian,

Turning the M2 into a minimum-phase device (ie linearizing the phase of the crossover) is pretty straightforward as the acoustical crossover is a text book 36dB/oct LR at 750Hz, pretty much.
Turning it into a fully linear-phase device requires you to also linearize the BR at around 25Hz.

Of course both modifications require a little bit more taps than the original minimum-phase settings, and an additional delay (~50ms for a fully linear-phase system).

I guess a phase discontinuity at 25hz is not going to have that big an impact on sound quality.

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