On 4/5/19 3:16 PM, Tim wrote:
> With a discussion about latency in the Jack lists, I thought
> I ask a question I've been wondering:
>
> By connecting a cable from a HW output to a HW input, one
> can measure the round-trip latency.
>
> But if the purpose is to try to determine the absolute
> latencies of the output port and the input port,
> by say, dividing the round-trip value by 2 and assuming
> this value applies to both ports, then won't this concept
> fail if the output port has a different latency than the
> input port? Say, by using two different devices for the
> input and output ports.
>
> I find myself asking what exactly transport position is and
> how it relates to the data in the outside physical world.
> I wonder if it would make sense to build an external
> hardware transport position indicator so that the latency
> test signals could be compared with it.
> For example to measure an output port's latency:
>
> ------>--[HW transport position indicator]-->---
> [PC]------- |
> --- | |
> | -->-[Audio output port]-------->---[Comparator]
> | |
> -----<--[Delay measurement]-------<-----------
>
> The remaining unknown - the input port latency would be
> given by subtracting this measured value from the total
> round-trip latency.
>
> Sound crazy?
> Thanks.
> Tim.
Here two or more low-latency-triggered precision oscillators
at non-harmonic related frequencies provide a signal to an
input and the software measures the group phase delay in
relation to the trigger time:
[PC] -->--[ex. Par. port]-->--[Triggers]-->--[Sin oscs]
--- |
| |
--<--[Audio input]---------------<---------
It's similar to how round-trip latency might be measured,
except there the sines are generated digitally by audio output.
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Received on Sat Apr 6 04:15:01 2019
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