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The making of: The Two Towers (a 25 driver Full Range line array)
The making of: The Two Towers (a 25 driver Full Range line array)
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Old 7th March 2020, 11:27 AM   #5821
TNT is offline TNT  Sweden
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Cool - thanks for sharing!!!

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Old 7th March 2020, 12:35 PM   #5822
wesayso is offline wesayso  Netherlands
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I hope it will get you some idea how to go about it.

To prove it can work with measured impulses I've used the theoretical sub and an actual measurement of the line array in an Overlay view of their filtered IR, where I've adjusted the timing of the array to fit the subwoofer:

The making of: The Two Towers (a 25 driver Full Range line array)-democrossover-jpg

See how it's still easy to align the shapes (identify them), even with an actual measured result at the listening spot? The slight wavy shape in front of the array measurement actually is pre-ringing of my phase correction, still the wave shape comes through undisturbed and is easily recognised and used for alignment without getting the timing wrong.

I know of no other way that could give you this kind of visual confirmation. It basically takes the guess work out of the equation.
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Old 7th March 2020, 01:18 PM   #5823
koldby is offline koldby  Denmark
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Quote:
Originally Posted by wesayso View Post
Koldby, did you try something like the DACT as well? I really want something I can trust to keep the balance right between the channels. The claims from the DATC are high.

I don't mind to get out of my chair, because I don't use the volume control that often during listening sessions, and I would not mind changing the digital volume in small steps. It's just when I use more attenuation, for instance a movie gets played less loud that music, due to the JRiver Volume Leveling not kicking in, I want an option to keep as many bits as I can.
Or if I want to play back at background levels I want to be able to attenuate without losing detail in the music.

I've noticed a big difference there, where the Goldmund sounded beautiful at lower levels, something I never experienced with the Pioneer. But the Pioneer already had the internal volume dialed back just like I plan to do with adding a pré-amp to make up that gain.

If the DACT is as good as they claim it is, I would be willing to fork out that price for admission.

I liked the basic thought of the simplicity of that devise. A DACT is claimed to have quite some precision:


Compared to Goldpoint:


Even though I can now understand what it is Bruno did, for me to replicate something like that for 6 channels would be quite the challenge.
Most certainly because of my possible mix of balanced and unbalanced connections.
I have not tried the DACT, but several other high quality stepped volumen controls and even though they are sounding good they never filled the bill for me , as the discrete steps were too coarse. Brunos preamp and the lightspeed attenuator are sounding a bit better, but no by a wide margin.
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Old 7th March 2020, 01:55 PM   #5824
TNT is offline TNT  Sweden
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When you sa " it can work with measured impulses" , do you mean a calculated impulse from a sweep? Is there a possibility for actual output of an impulse from REW?

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Old 7th March 2020, 02:02 PM   #5825
mark100 is offline mark100  United States
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The making of: The Two Towers (a 25 driver Full Range line array)
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Originally Posted by TNT View Post
Blatant knowledge theft

To time-align sub with main (main fixed, sub delay changeable)

Align as A or B - never got that really... on the peak or on the start?
Super question imo
Get's at the root of understanding phase and timing....a question Wesayso helped me solve/understand several years back.

The simple answer.
Correct time alignment is when starts are aligned.
Not peaks.

The well noted problem is that our measurement programs key off impulse peaks.
And peaks get less and less defined, as high frequency response is taken away. Which makes defining impulse starts even more difficult than tagging peaks.

Ime, impulse responses are the wrong tool to use for fine time alignment.

They are useful as a quick start to get into the correct time alignment ballpark, by helping to remove excess delay.
But once that excess delay is removed, phase traces are an easier/better way to achieve impulse start alignments, than trying to continue to analyze impulse (or step, or group delay, etc).

When phase traces lay on top of each other as closely as possible through the xover region, impulse start alignment has been accomplished as well as can.

Aligning phase traces is a task that dual channel FFT's handle much better than sine sweeps, again ime...
They make better phase traces down low, since dual FFT allows continuous real time transfer functions. Temporal averaging of the continuous measurement can be used for very good stability and repeat-ability.

Even better, real time phase traces allow you align phase by having one section's (say sub) captured trace up on screen, while measuring the other's (main) trace in real time, and simply dialing processor delay on the leading section until the phase traces overlay.

After using the match phase trace method, I've used REW to confirm and peer into bandwidth filtered impulses like in Wesayo's good explanation.
All jives together fine. Both methods work.
But wow, is dual FFT easier. just another fwiw
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Old 7th March 2020, 02:24 PM   #5826
mark100 is offline mark100  United States
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The making of: The Two Towers (a 25 driver Full Range line array)
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Originally Posted by wesayso View Post
Interesting and affordable suggestion... here I was only looking at volume controls like this:
Click the image to open in full size.

Simple, basic but expensive...
Wow ! and yikes ! I couldn't imagine doing something like that.

I might have been misleading when I was talking about gain staging and the need for analog attenuation after the digital stage (to match amp sensitivity.)

When I look at block diagrams of DSP processors, there is usually a DAC input block, then a DSP processing ouput block (EQ's xovers, dynamics, etc), then a final DAC output block for digital attenuation that essentially becomes analog attenuation.

Instructions are invariably to keep the DAC input block just below 0dBFS, and then the same for adjusting output of the DSP processing block.
The last block becomes the the "volume control", and is still digital.

Whether there are actual separate blocks I dunno...I leave that to folks like Fluid, Kolby, BYRTT, et al...

I do know my processor allows meters to be placed at those points (real or virtual) for optimizing gain staging.
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Old 7th March 2020, 02:35 PM   #5827
nc535 is offline nc535
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Really good tutorial Ronald. You may recall explaining it to me a few years ago and I couldn't get it to work for me. In my defense then it turns out I had a ceiling reflection coming in at the LP and causing phase difficulties at XO. But this explanation is perfectly clear and even I can follow it. But I ended up aligning on impulse start. It would be interesting to compare results with the two methods.

Changing the subject - thanks all for interesting discussion on volume control

Audio Bitdepth - JRiverWiki

You can't run out of digital headroom but if you use any of it for volume control, that will bring the DAC's output signal closer to the DAC's noise floor and thus degrade the SNR. Does it matter enough to merit design and construction of a multi-channel preamp? Better to design a DAC board with volume control integrated into the DAC's current to voltage conversion and buffering stages.
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Old 7th March 2020, 03:22 PM   #5828
mark100 is offline mark100  United States
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The making of: The Two Towers (a 25 driver Full Range line array)
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Originally Posted by nc535 View Post
Changing the subject - thanks all for interesting discussion on volume control

Audio Bitdepth - JRiverWiki

You can't run out of digital headroom but if you use any of it for volume control, that will bring the DAC's output signal closer to the DAC's noise floor and thus degrade the SNR. Does it matter enough to merit design and construction of a multi-channel preamp? Better to design a DAC board with volume control integrated into the DAC's current to voltage conversion and buffering stages.
Should have known/remembered this stuff is up your alley!

So it looks like there is an actual distinct volume control block post all DSP processing.



You know, here's an off the beaten track recommendation for a home audio multi-channel DAC, I/O box, and bit of a DSP processor.
The Behringer XR-18 stagebox mixer.

18x18 USB. 18x8 balanced I/O.
Decent EQs and Xovers.
Full fledged mixer/routing capability.
Very good ethernet control via PC or Mac, Behringer apps..
Excellent wireless tablet control with built in wifi, and $5 Mixing Station Pro app.
All for under $600..
Good sound card for REW too
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Old 7th March 2020, 04:55 PM   #5829
wesayso is offline wesayso  Netherlands
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I don't think my plan here with a volume control is that wild. Do remember that up to 15-17 dB of my digital headroom is locked up in DSP (used to be about 25 dB even) with a 20 bit available in the DAC.

Get another DAC would be a simple and truly reasonable suggestion. But... not all amps sound alike and certainly not all DAC's sound alike. I do know what I've got here (and value it).

So the analog attenuation has become something on my mind due to the most recent experiences. Once you use up too many bits inside that digital room you don't get the output you should have. No way around that with the current means. I don't have a system here that needs only a little wiggle room, I use up a lot of internal space. And I like it that way, but I can win quality at lower levels by taking the analog attenuation outside of the digital realm.
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Old 7th March 2020, 05:40 PM   #5830
wesayso is offline wesayso  Netherlands
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Let's be honest here, we all do what we do, and even though we might have similar systems, each of us has made different choices for a similar problem.
None of us use the same equipment. Why is that?

My way forward is and will continue to be to identify a weak spot and fix it. One thing at a time. Introducing an all new DAC is changing way more than one variable. In other words: I cannot control that. Changing one variable at a time and confirm what it does (roll back if needed) has been my method of choice.

Changing more than one variable at a time means we do not learn what was fixed. I like to learn .
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Last edited by wesayso; 7th March 2020 at 05:45 PM.
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