Discussion:
latency
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Alex Dashevski
2018-10-06 11:22:00 UTC
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Hi,
I made measurements on nexsus 4 on the audio-echo project from google ndk
examples and I got the following restult:
SampleRate buff length[samples] latency [ms]
48Khz 240 66
48Khz 2400 225.8
48Khz 4800 389
48Khz 7200 576
48Khz 9600 783
48Khz 24000 2000
The first line is the recommended parameter of the system(fast path). Could
you explain the meaning of the fast path ?

Every time , I multiplied by whole multiples of 10 the buffer size.
My question is: How can I explain the differance of latency ? Why is there
no corroletion of the latency ?

Thanks,
Alex
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'Phil Burk' via android-ndk
2018-10-08 14:18:33 UTC
Permalink
Hello Alex,

The latency is the sum of all the frames of audio data in all the buffers
between the application and the speaker. Bigger buffers lead to bigger
latency.

Some of the latency is in your giant buffers. Some is in internal buffers
in AudioFlinger and the DSP. They are probably much smaller.

Try plotting your data. The y-intercept of that line will tell you the
internal latency.

There can be multiple levels of mixing in AudioFlinger. The regular mixers
handle effects, sample rate conversion, etc. They feed into a "FAST" mixer
with smaller buffers. If your track is not doing any effects or sample rate
conversion then it can go straight to the FAST mixer if you request
LOW_LATENCY.

Phil Burk
Post by Alex Dashevski
Hi,
I made measurements on nexsus 4 on the audio-echo project from google ndk
SampleRate buff length[samples] latency [ms]
48Khz 240 66
48Khz 2400 225.8
48Khz 4800 389
48Khz 7200 576
48Khz 9600 783
48Khz 24000 2000
The first line is the recommended parameter of the system(fast path).
Could you explain the meaning of the fast path ?
Every time , I multiplied by whole multiples of 10 the buffer size.
My question is: How can I explain the differance of latency ? Why is there
no corroletion of the latency ?
Thanks,
Alex
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Alex Dashevski
2018-10-08 14:24:03 UTC
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And ?
How can I explain big difference between first line and second line ?
Can you point me to good acticle that explain meaning of the fast path ?
Thanks,
Alex

‫בתאךיך יום ב׳, 8 באוק׳ 2018 ב-17:18 מאת ‪'Phil Burk' via android-ndk‬‏ <‪
Post by 'Phil Burk' via android-ndk
Hello Alex,
The latency is the sum of all the frames of audio data in all the buffers
between the application and the speaker. Bigger buffers lead to bigger
latency.
Some of the latency is in your giant buffers. Some is in internal buffers
in AudioFlinger and the DSP. They are probably much smaller.
Try plotting your data. The y-intercept of that line will tell you the
internal latency.
There can be multiple levels of mixing in AudioFlinger. The regular mixers
handle effects, sample rate conversion, etc. They feed into a "FAST" mixer
with smaller buffers. If your track is not doing any effects or sample rate
conversion then it can go straight to the FAST mixer if you request
LOW_LATENCY.
Phil Burk
Post by Alex Dashevski
Hi,
I made measurements on nexsus 4 on the audio-echo project from google ndk
SampleRate buff length[samples] latency [ms]
48Khz 240 66
48Khz 2400 225.8
48Khz 4800 389
48Khz 7200 576
48Khz 9600 783
48Khz 24000 2000
The first line is the recommended parameter of the system(fast path).
Could you explain the meaning of the fast path ?
Every time , I multiplied by whole multiples of 10 the buffer size.
My question is: How can I explain the differance of latency ? Why is
there no corroletion of the latency ?
Thanks,
Alex
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