Re: [LAD] No nagging, a serious question

On Sun, 2010-07-04 at 23:05 +0100, Dan Mills wrote:
> On Sun, 2010-07-04 at 23:35 +0200, fons@email-addr-hidden wrote:
>
> > Well, at least those sound cards that provide both audio and midi
> > *could* do this - timestamp incoming midi and provide that info
> > in some way, and requiring similar time stamps for outgoing midi.
>
> Could do it even with separate midi and audio cards, as long as the midi
> RX ISR can somehow grab a timestamp from the audio card driver (in an
> interrupt context), and as long as the midi RX ISR is getting serviced
> with negligible latency (Otherwise you need to timestamp in hardware).
>
> In reality is is probably only practical in an embedded context where
> you have total control over the hardware.
>
> Note that even with this you will have some jitter due to the way a UART
> typically over samples to get the centre location of each bit (But at
> midi rates this should only be measured in tens of microseconds).
>
> MIDI on general purpose hardware with a general purpose OS is hard to
> get really right.
>
> Regards, Dan.

I'll try to use 2 of this Audio/MIDI cards:
http://www.terratec.net/en/driver-and-support/faq_37196.html?selectproduct=EWX%2024/96

It would be nice to use both for audio, but the original thought to get
a second card is, to use only one card for audio + MIDI and the other
card for MIDI only, to get two independent MIDI outputs.

If it should be ok to use two cards, a test will show, I assume that
even if audio isn't used, audio for those two cards needs to be synced
at least by S/PDIF?

OT:

Not my machine ...

> ### First the RME results ###
> $ alsa-midi-latency-test -i 16:0 -o 16:0 -w 20 -r

> > SUCCESS
>
> best latency was 0.96 ms
> worst latency was 4.04 ms, which is great.

> ### Next are the midisport results ###
> $ alsa-midi-latency-test -i 28:1 -o 28:1 -w 20 -r

> > FAIL
>
> best latency was 2.95 ms
> worst latency was 34.96 ms, which is too much. Please check

... IIRC I had around 19 ms for the worst USB MIDI latency. The PCI card
should be tested tomorrow. Even if some had good latencies for USB too,
it seems to be gambling using USB MIDI devices. IIRC all PCI devices had
SUCCESS.

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Received on Mon Jul 5 04:15:02 2010