[[see also latency test results for USB 1.0 devices Emagic MT-4 and Edirol UM-2, below reply]]
On Wed, Jun 30, 2010 at 12:26 AM, Ralf Mardorf <[email protected]> wrote: > You say I can use my ElCheapo EWX 24/96 with another ElCheapo for audio, > by any other vendor, just by connecting S/PDIF to sync the channels? I don't think that is possible, except by luck. I meant two of the same brand/manufacturer cheapo cards with SPDIF ins, e.g. two or three Delta-66's (nb: no vt17212 midi), to or three Dmx6Fire's (one vt1712 real midi, one ttl midi), or Audiophile 24/96's (one vt1712 real midi).... It is possible that you could do this with multiple cards all using snd-ice1712 -- because anything's possible and you have the sourcecode to the drivers... :-) > FWIW, there aren't jumpers on the Terratec and I guess the used MPU by > the two provided by the EnvyChip is broken. For my old mobo's gameport I > soldered an adapter without TTLs and opto-couplers. This cable wasn't > fine for the Terratec, hence I took my BreadBoard and checked several > circuits, without TTLs, but opto-couplers. One big issue is that real MIDI is a current-loop interface, with the optocoupler allowing completely independent circuits to be connected w/o creating ground loops and less potential to induce noise from other connected machines. Devices expecting a current-loop are not going to function properly when given TTL levels. You could probably fake something up w/ TTL bus-drivers, but what's the point -- there's probably a zillion game cable ports available for sale uses.... ---------------------------------------------------------------------- FYI, regarding MIDI latency: some USB tests first (since the 1712-basedDMX6Fire is now waiting for a machine to house it). Note that each test doesn't have a lot of variation, but there are single outliers that indicate the potential for a very occasional few extra ms of jitter. Note that jitter is additive... in that if you're trying to come up with worst-case timing specifications, you need to add all the best cases observed to come up with the overall best case, and all the worst cases observed to come up with an overall worst case. As you add layers and multiple devices all "chained" you can end up with a massive "jitter multiplication effect" where you can't hear any of the individual worst cases, but they'll all manage to coalesce into the worst case -- usually just in time for an important demo/concert/software-release/etc. One of the other properties of jitter is that it likes to stay dormant until something really important is going to fail because you didn't take it into account. Trimming out jitter at the device or OS level is certainly worthwhile given jitter's additive properties. Add enough worst case hardware jitters, worst-case kernel latency and jitter, application level latency and jitter, and you could easily come up with a jitter value that is within human ranges of perception. The test confirms that Emagic's USB Midi devices work as well spec-wise as they do physically (a highly recommended USB MIDI box -- cost about $25.00 on e-bay, vs. $30.00 for the UM-2 with two fewer output ports). Using: > alsa-midi-latency-test 0.0.3 > set_realtime_priority(SCHED_FIFO, 99).. done. > clock resolution: 0.000000001 s On host using ASUS M4A78T-E motherboard and AMD Phenom-II processor running stock Fedora 12 kernel: > Linux gnulem 2.6.32.14-127.fc12.x86_64 #1 SMP Fri May 28 04:30:39 UTC 2010 > x86_64 x86_64 x86_64 GNU/Linux A) Edirol UM-2 ( http://qbik.ch/usb/devices/showdev.php?id=1244 ) (NB: tested using an illegally-long 30-foot USB cable -- that works fine with the UM-2 slow USB device). Device: 36:0 UM-2 UM-2 MIDI 1 Command: alsa-midi-latency-test -w -r -R -i 36:0 -o 36:0 Test1) ... 2.5 - 2.6 ms: 1 # ... 2.9 - 3.0 ms: 61 # 3.0 - 3.1 ms: 9938 ################################################## best latency was 2.46 ms worst latency was 3.03 ms, which is great. Test2) ... 2.9 - 3.0 ms: 61 # 3.0 - 3.1 ms: 9938 ################################################## ... 4.0 - 4.1 ms: 1 # best latency was 2.88 ms worst latency was 4.00 ms, which is great. Test3) ... 2.7 - 2.8 ms: 1 # ... 2.9 - 3.0 ms: 60 # 3.0 - 3.1 ms: 9938 ################################################## ... 4.0 - 4.1 ms: 1 # best latency was 2.69 ms worst latency was 4.00 ms, which is great. Test4) ... 2.7 - 2.8 ms: 1 # ... 2.9 - 3.0 ms: 60 # 3.0 - 3.1 ms: 9939 ################################################## best latency was 2.73 ms worst latency was 3.03 ms, which is great. ---------------------------------------------------------------------- B) Emagic MT-4 ( http://qbik.ch/usb/devices/showdev.php?id=3171 ) Device: 28:0 MT4 MT4 MIDI 1 Command: alsa-midi-latency-test -w -r -R -i 28:0 -o 28:0 Test1) ... 1.5 - 1.6 ms: 2 # ... 1.9 - 2.0 ms: 42 # 2.0 - 2.1 ms: 9953 ################################################## 2.1 - 2.2 ms: 1 # ... 2.6 - 2.7 ms: 1 # ... 2.9 - 3.0 ms: 1 # best latency was 1.50 ms worst latency was 2.88 ms, which is great. Test2) ... 1.9 - 2.0 ms: 41 # 2.0 - 2.1 ms: 9957 ################################################## ... 3.0 - 3.1 ms: 2 # best latency was 1.88 ms worst latency was 3.00 ms, which is great. Test3) ... 1.5 - 1.6 ms: 1 # ... 1.9 - 2.0 ms: 42 # 2.0 - 2.1 ms: 9956 ################################################## ... 3.0 - 3.1 ms: 1 # best latency was 1.45 ms worst latency was 2.99 ms, which is great. Test4) ... 1.9 - 2.0 ms: 41 # 2.0 - 2.1 ms: 9956 ################################################## 2.1 - 2.2 ms: 1 # 2.2 - 2.3 ms: 1 # ... 3.0 - 3.1 ms: 1 # best latency was 1.88 ms worst latency was 2.99 ms, which is great. -- Niels http://nielsmayer.com _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
