Latency, delay, synchronization, time alignment are always critically important in multichannel DAC system with DSP at upstream digital domain within PC.
Please note that my discussion here is limited to pure audio-only system, and excluding audio-visual system where you need "time alignment adjustment" not only for the SPs but also for visual images/movies.
In the audio digital signal processing, we have so many buffers or latencies; JRiver output buffer, ASIO4ALL's I/O buffers, DSP's (in my case EKIO's) processing buffer, DIYINHK USB ASIO driver's buffer, and so on. It is not straightforward, therefore, to exactly measure the "absolute delay" between the JRiver's "shout" and the final air sound kick-up by SP.
As for the synchronization between the channels...
In my system using OKTO DAC8PRO (firmware 1.32) and DSP software EKIO feeding the cross-overed (EQ-ed) 8 channels into DAC8PRO through DIYIHNK USB ASIO multichannel driver, I have no synchronization issue; all the 8 channels are in complete sync.
I usually set all the buffers in the digital domain in rather large size, so that I should not have any latency or delay problems; in our audio setup, we have no problem at all if all the bunch of the digital and analog signal (15Hz - 30 kHz) have identical amount of delay time from the signal origin at music player such as JRiver, and this is always the case in our digital (PC based) audio system.
The
relative delay between the sound of SP units, or
"time alignment" in multiple SPs, however, is always one of the critical issues in audio system, especially in the multichannel multi-driver multi-amplifier system, as you may agree.
Even though some of the advanced audio measurement software, like REW and Equalizer APO, feature some kind of "delay and/or time alignment" measurement(s) (using microphone) between the SP units, the internal procedure for the measurement would be somewhat "black-box", and if it includes "absolute delay measurement" type approach, the given "delay and/or time alignment" results are not always accurate and stable; this issue have been well pointed by
@zerxia in his post
here and
here. He wrote,
"Through this test, I found that the channel delay displayed by the Equalizer APO is not accurate."
Consequently, we need to have reliable reproducible high-precision (0.1 msec to 1 msec precision) measurement method(s) for
the relative delay (time alignment) by using
only the air recorded room sound with measurement microphone together with reliable audio interface (ADC) of fixed latency.
Having the above mentioned issues in my mind, I recently developed rather primitive but really accurate reproducible measurement method for time alignment between the SP units by
using only the air recorded sound analyzed with Adobe Audition 3.01 (or Audacity, if you like).
If you would be interested, please visit these posts on my project thread;
- Precision measurement and adjustment of time alignment for speaker (SP) units:
Part-1_ Precision pulse wave matching method:
#493
- Precision measurement and adjustment of time alignment for speaker (SP) units:
Part-2_ Energy peak matching method:
#494
- Precision measurement and adjustment of time alignment for speaker (SP) units:
Part-3_ Precision single sine wave matching method in 0.1 msec accuracy:
#504,
#507
Please simply PM me, if you would be seriously interested in using the test tone signals I prepared and used in my above time alignment measurements.