This post space is reserved for my response to
@Adahn.

Hopefully I will respond to you this evening after completing my rather busy end-of-the-year business and private duties (my wife is serious!) today...
OK, now I am back!
In order to properly and adequately respond to your kind inquiry, I believe I need talking briefly about my “historic” sequences in time-alignment (and phase-continuity) measurements and tunings in my
multichannel multi-SP-driver multi-amplifier full-active stereo audio system.
Even before I could get OKTO DAC8PRO (8-Ch sync DAC unit), I semi-objectively measured and noticed through REW’s wavelet analysis of room air sound that the sound of my L&R sub-woofers delays about 15 msec – 25 msec against the main SP system (ref.
#17,
#18,
#20,
#21,
#22).
After the arrival of OKTO DAC8PRO at my listening room in May 2020 (ref.
#92), I explored my rather long and intensive journey towards selection and determination of four amplifiers to dedicatedly and directly drive woofers, midranges, tweeters and super-tweeters (my L&R large and heavy sub-woofers, YAMAHA YST-SW1000 has built-in powerful amplifiers). You can find the summary of my amplifier selection journey based on my policy of
“right-person-in-right-place” in my post
#311 and
#413; throughout the journey I have been using JRiver MC, ASIO4ALL, DSP “EKIO” and DAC8PRO,
i.e. I have/had no trigger-lag nor sync-drift issue among the eight (8) DAC channels.
Then, after I almost completed/established my multichannel audio system in January 2022 (ref.
#508), I decided to perform rather intensive measurements and tunings on time-alignments (and phase-continuities) among all of the five SP drivers (
i.e. sub-woofer, woofer, midrange, tweeter and super-tweeter) by my somewhat unique but fully validated reliable reproducible measurement methods; I would like to avoid any loop-back analysis like REW does/did, but would like to establish my own primitive and simple reliable methods.
I started such approach firstly for the time-alignment between sub-woofer to main SP’s woofer in 1 msec precision applying
“Precision Time-shifted Multiple Fq Rectangular Sine Tone Burst Method” (ref.
#493), and also applying
“Tone Burst Energy Peak Matching Method” (ref.
#494). Both of the two methods unanimously gave the result that the subwoofer sound delays
16.0 msec against main SP system, and hence the 16.0 msec group delay settings in DSP “EKIO” for woofer, midrange, tweeter and super-tweeter have been justified for time-alignment with subwoofer.
Next, I moved on to 0.1 msec precision time-alignment between woofer and midrange by applying
“Precision Single Sine Wave Matching Method” (ref.
#504). I believe this method is a kind of ultimate method/goal for not only precision time-alignment but also for optimization of phase-continuity between the two SP drivers controlled by upstream DSP, and several people in ASR agreed it is so. As the results, I found that my woofer delays
0.3 msec against midrange, and there were/are no delay between midrange, tweeter and super-tweeter (in 0.1 msec precision which is more than enough precision).
Consequently, I could find/confirm that group delay DSP settings of
0.00 msec (none) for subwoofer,
16.0 msec for woofer,
16.3 msec for midrange,
16.3 msec for tweeter and
16.3 msec for super-tweeter were/are the optimal for time-alignment (as well as phase continuity) among all the SP drivers in my own multichannel audio setup.
I also found that the
“Precision Single (or Three, Eight) Sine Wave Matching Method” and the 3D-color spectrum analysis (representing 3D sound energy distribution) thereof using ADOBE Audition 3.0.1 are also very much effective and powerful in assessment of transient characteristics (step response) of subwoofers and woofers, as well as for determination of optimal crossover Fq (ref.
#504,
#507,
#495,
#497).
I myself, as well as my wife and several audio enthusiast colleagues/musicians, can subjectively find/hear the great benefit of such complete time-alignment among the all SP drivers, for example as shared in my posts
#520 and
#687.
- Perfect (0.1 msec precision) time alignment of all the SP drivers greatly contributes to amazing disappearance of SPs, tightness and cleanliness of the sound, and superior 3D sound stage: #520
- Not only the precision (0.1 msec level) time alignment over all the SP drivers but also SP facing directions and sound-deadening space behind the SPs plus behind our listening position would be critically important for effective (perfect?) disappearance of speakers: #687
BTW, for subjective listening tests/evaluations, I have been using my own consistent
“Audio Reference/Sampler Music Playlist” consists of 60 music tracks selected from various genres having excellent recording quality; I have dedicated thread (ref.
here #1 on that independent thread) on such audio reference playlist.
Of course, the pros of my such time-alignment tunings remained unchanged when I implemented wide-3D reflective dispersion of super-tweeter sound using random-surface hard-heavy crystal glass material enabling improved/better stereo sound perspective/image (ref.
#921,
#926,
#927,
#929).
After briefly talking all the above, and after your kind understanding on the above, now I shall go into my response to your present inquiry.
In September 2023, while I was fully enjoying music listening with thus established my main multichannel audio setup, just for my personal curiosity (nothing more, nothing less) I thought again about my long-lasting interest on
“possible (or not) synchronization of multiple independent DAC units (each has independent ASIO driver) in Windows-PC-based audio setup”.
I decided performing my rather strict “experiments” on this regard (completely in outside of my main audio system) as I shared in my posts
#783 and
#804 which you have been already reading through; at that time, I was still using ASIO4ALL as system-wide ASIO routing center.
Now you can understand why I was/am concerning about possible synchronization of multiple independent DAC units in 0.1 msec precision/accuracy; please be reminded that I have established 0.1 msec precision time-alignments in my main audio system, and therefore I need 0.1-msec-level precision of synchronization if it might be possible to synchronize multiple independent DAC units.
As you are already aware of, unfortunately, even using ASIO4ALL, I clearly measured/observed the “trigger lags” between the multiple independent DAC units; the “synchronization drift” after the trigger through the end of the music track, however, was negligible/undetectable; I mean the “trigger lags” were/are strictly kept throughout the playback of the music track. In any way, as far as we have “trigger lags”, we should not use such multiple independent DAC units in our PC ASIO driver based audio system.
This “trigger lag” measurements led me to the compromise of quasi-synchronization (or I should say sham-synchronization) of multiple independent DAC units in 0.1 msec precision by applying suitable “group delay” in upstream DSP configuration, but such compromise is valid only if the “trigger lags” would be strictly maintained/kept unchanged throughout our audio listening sessions on the day, and/or weeks, months, in the specific audio setup; we need to strictly “measure” the “trigger lags” to be compensated by DSP’s group-delay settings every time before our listening session, and we should confirm it has been maintained/kept at the end of the listening session.
Consequently, such DSP-based quasi-compensation of “trigger lags” would not be useful for our daily music listening sessions, and definitely it should not be recommended for our daily utilization; I mean that I could found the way of DSP-based tentative compensation of trigger-lags only for my curiosity.
After all the above, I replaced ASIO4ALL by VB-AUDIO MATRIX because of much better GUI operation in MATRIX as well as its stability/robustness as system-wide ASIO/VASIO/VAIO routing center (ref.
#851,
#854 and
#858).
Recently, on November 27, when I received the update notice from VB-AUDIO on their MATRIX 1.0.2.5, I was rather impressed by their description of better/improved “synchronization” among the ASIO, VASIO, VAIO physical/virtual audio devices (ref.
#1,016) which led me to the similar measurements (ref.
#1,021) just like I have done in September 2023 using ASIO4ALL (ref.
#783,
#804); I had faint expectation of possible “trigger synchronization” by VB-MATRIX 1.0.2.5 among the multiple independent DAC units each has its own ASIO (and/or WDM/WASAPI) drivers.
Unfortunately, as shared in detail in my post
#1,021, even using “Internal Clock” as sync-Master in VB-MATRIX 1.0.2.5, the “trigger lags” still do exist among the multiple DAC units which was also confirmed by kind response given by one of the VB-AUDIO’s engineering staffs as follows;
The ”Strict” synchronization feature of VB-MATRIX 1.0.2.5 is not intending your point of trigger synchronization of multiple USB-DAC units; VB-MATRIX strictly simultaneously sends the music (sound) track into connected multiple DAC units, but the exact trigger timing of each DAC would be dependent on its own ASIO or WDM (WASAPI) drivers as well as Windows audio playback priorities which are out of control by VB-MATRIX, as you have suggested.
Consequently, just as you find in your posts #783 and #804, there would be always some trigger timing lags between the USB-DAC units unless otherwise they have some “sync trigger” mechanism with each other through their ASIO driver just like you have already described in your post #842 for RME Fireface UFX III.
In VB-MATRIX side, however, you may optimize/minimize the “trigger timing lags” by settings VAIO sync option to “STRICT” and change Matrix Latency Performance Mode to “Optimal”.
Consequently, as I wrote in
#1,021, my present “conclusions” are;
Even with VB-MATRIX 1.0.2.5, we cannot exactly/strictly synchronize the “triggers” of multiple independent USB-DAC units; the trigger timing lags depend on each ASIO and/or WDM (WASAPI) driver as well as Windows audio playback priority orders.
We can optimize/minimize the trigger timing lags by VB-MATRIX’s sync option “STRICT” and latency performance “Optimal”.
And as I wrote
here #389 on the remote thread, I believe we should clearly separate the two points/issues in this regard of multiple-channel DAC processing;
1. trigger (kick-off/start-up) synchronization (or not) among the DAC channels, even if the strict synchronization (drift correction) could be achieved afterwards,
2. clock synchronization = drift correction among the multiple DAC channels after starting/triggering playback of a music track.
I also wrote
there as follows;
We can completely "solve" both of 1. and 2. by using sync multichannel DAC unit like OKTO DAC8PRO (I use it), TOPPING DM7, all-new MOTU 16A, etc. all of which have dedicated multichannel USB ASIO driver.
We can also "solve" the issues if we can achieve all synchronized AES/EBU digital inputs into the multichannel DAC (or such multiple DAC units) if they have AES/EBU digital inputs (like OKTO DAC8PRO), since AES/EBU digital signal contains clock sync pulses in it. This has been widely achieved in pro audio market in multichannel recording and sound editing.
Furthermore, even in the case of USB ASIO configuration, we can fully synchronize certain "same brand" multiple DAC units (like RME Fireface UFX III) if they have some "sync trigger and drift correction" mechanism with each other through their dedicated USB ASIO driver (ref. #842 on my project thread). In the case, each of the multiple DAC units needs to be connected to USB ports of PC (or Mac) so that the ASIO driver can recognize all the sync-aggregated DAC channels.
Furthermore, I also wrote in my post
#393 on that thread as follows;
You would please do not be too much "strict" on your audio system.
You may use multiple DAC units (with preamplifier gain controls) if the trigger timing difference(s)/lag(s) and the possible synchronization drift(s) are within acceptable time scale, say within 10 msec, and if you have no audible "issues" on it. You would please trust your own "subjective listening preference" with your ears and brain at your listening position. Our ears and brain are not identical to measurement microphone and sound analysis software.
Objective measurements of trigger mismatch and/or drift of synchronization (or not), however, would be worthwhile to objectively know the "actual room sound status" of your system with which you usually enjoy music listening excitements. Based on such objective data, sometimes further tuning would be possible for better subjective assessment/feeling of the system-sound in your acoustic listening environments.
I hope all the above would be properly and adequately responding to your present kind inquiry.
Edit:
You would please find in
#931 and
#1,009 the details of my latest system setup.
You can find
here and
here the Hyperlink Index for my project thread.