Round-trip latency of USB Audio is not stable
Posted: Wed Dec 21, 2016 12:08 pm
Hello.
I'm checking the round-trip latency of USB Audio with XK-AUDIO-216-MC and PC (Windows 7 Pro SP1).
I added loop-back to the mixer module of XMOS FW - USB Audio 2.0 Device Software Ver.6.12.5, and measured interval between USB Audio Out and In.
I used Thesycon USB ASIO Driver Ver.3.34. Following is the setting of TUSBAudio Control Panel and round-trip latency (USB Audio Out - In) and total latency of application at 44100Hz sample rate.
<Sample Rate: 44100Hz, USB Streaming Mode: Minimum Latency, ASIO Buffer Size: Auto>
USB Audio Out - IN: 498us
Total Latency of App: 273samples
I tried about 10 times, the results were stable - 498us. Then, I changed sample rate like following, and measured again.
44100Hz => 48000Hz => 44100Hz
<Sample Rate: 44100Hz, USB Streaming Mode: Minimum Latency, ASIO Buffer Size: Auto>
USB Audio Out - IN: 373us
Total Latency of App: 267samples
I tried about 10 times, the results were stable - 373us.
It seems that this change is occurred by reopening USB Audio stream and changing sample rate.
Why is the round-trip latency in XMOS changed? Host PC shouldn't affect this latency.
I changed the USB Streaming Mode of TUSBAudio Control Panel to Extra Safe.
<Sample Rate: 44100Hz, USB Streaming Mode: Extra Safe, ASIO Buffer Size: Auto>
USB Audio Out - IN: 498us
Total Latency of App: 5869samples
44100Hz => 48000Hz => 44100Hz
<Sample Rate: 44100Hz, USB Streaming Mode: Extra Safe, ASIO Buffer Size: Auto>
USB Audio Out - IN: 373us
Total Latency of App: 5862samples
Difference of the round-trip latency (USB Audio Out - In) is 125us (=5.5125samples at 44100Hz).
Difference of the total latency of application is 6 or 7 samples.
They are nearly equal. I would like to the round-trip latency be stable.
I added zip file which include png files of USB log.
Thank you in advance.
I'm checking the round-trip latency of USB Audio with XK-AUDIO-216-MC and PC (Windows 7 Pro SP1).
I added loop-back to the mixer module of XMOS FW - USB Audio 2.0 Device Software Ver.6.12.5, and measured interval between USB Audio Out and In.
I used Thesycon USB ASIO Driver Ver.3.34. Following is the setting of TUSBAudio Control Panel and round-trip latency (USB Audio Out - In) and total latency of application at 44100Hz sample rate.
<Sample Rate: 44100Hz, USB Streaming Mode: Minimum Latency, ASIO Buffer Size: Auto>
USB Audio Out - IN: 498us
Total Latency of App: 273samples
I tried about 10 times, the results were stable - 498us. Then, I changed sample rate like following, and measured again.
44100Hz => 48000Hz => 44100Hz
<Sample Rate: 44100Hz, USB Streaming Mode: Minimum Latency, ASIO Buffer Size: Auto>
USB Audio Out - IN: 373us
Total Latency of App: 267samples
I tried about 10 times, the results were stable - 373us.
It seems that this change is occurred by reopening USB Audio stream and changing sample rate.
Why is the round-trip latency in XMOS changed? Host PC shouldn't affect this latency.
I changed the USB Streaming Mode of TUSBAudio Control Panel to Extra Safe.
<Sample Rate: 44100Hz, USB Streaming Mode: Extra Safe, ASIO Buffer Size: Auto>
USB Audio Out - IN: 498us
Total Latency of App: 5869samples
44100Hz => 48000Hz => 44100Hz
<Sample Rate: 44100Hz, USB Streaming Mode: Extra Safe, ASIO Buffer Size: Auto>
USB Audio Out - IN: 373us
Total Latency of App: 5862samples
Difference of the round-trip latency (USB Audio Out - In) is 125us (=5.5125samples at 44100Hz).
Difference of the total latency of application is 6 or 7 samples.
They are nearly equal. I would like to the round-trip latency be stable.
I added zip file which include png files of USB log.
Thank you in advance.