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Topic: Latency vs. Legato -- Important read for everyone

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  1. #1

    Exclamation Latency vs. Legato -- Important read for everyone

    I think I may have made an important discovery regarding GPO legato mode and latency settings in sequencers. Please note that I have not rigorously tested this, but early research suggests the below findings. I am using Sonar 5 Producer Edition, but I strongly suspect this will affect users of any sequencer.

    I at one point noticed that at very high latency settings, the legato function seems to not work. I am talking in the neighborhood of 150ms+. I rarely work with such high latencies, but if I'm editing a huge score and haven't frozen many tracks, I might bump it up temporarily. But now I think I've found a direct correlation between the latency setting and how legato functions.

    It seems that the time between a sustain-on message (ctrl#64=127) and the beginning of a note must be greater than the effective latency for legato to work.

    Let's take an example: Suppose you have a piece whose tempo is 120 bpm and you have a legato run of sixteenth notes. There will be about 125 ms between the beginning of each note. If you place a ctrl#64 message exactly between the first and second note, you have about a 62 ms "clearance" before the second note sounds. In this example, any latency setting above 62 will cause the legato to not function for the second note (though it seems to kick in for the third, if legato is held).

    Now 62 ms is pretty high, and most use a much lower setting. However, if the message had been placed closer to the second note, or if the tempo were faster, or if 32nd notes were used, your clearance would become much smaller. For very quick alternating tongued and slurred notes in a woodwind instrument, you will have to be very careful about controller placement, or the slurred notes will break apart, or even be lost all together.

    This problem can definitely be worked around, so I thought I'd spare folks a little grief if they are having trouble with legato. I'd be curious if anyone has anything to add to this experiment, conflicting or supporting.
    - Jamie Kowalski

    All Hands Music - Kowalski on the web
    The Ear Is Always Correct - Writings on composition

  2. #2

    Re: Latency vs. Legato -- Important read for everyone

    Jamie,
    For some reason, your observations caused me to remember
    this interesting, if terse, article about the affects of high latency...not that it explains your observations. This affect--jitter--can be reproduced at latency well below the 150ms level that you refer to. Perhaps the irregularity in the timing of the samples that can be introduced at high latency can affect the perception of the legato.
    Bill

  3. #3

    Re: Latency vs. Legato -- Important read for everyone

    Definitely an interesting read, but not likely a related problem.

    The legato layer engaging either works, or it doesn't. It's like a switch that fails if it is thown too late.
    - Jamie Kowalski

    All Hands Music - Kowalski on the web
    The Ear Is Always Correct - Writings on composition

  4. #4

    Re: Latency vs. Legato -- Important read for everyone

    Quote Originally Posted by Skysaw
    The legato layer engaging either works, or it doesn't.
    Jamie,
    This may interest you:




    NV Flute, 16th notes @ 120bpm; 960ticks/quarter
    No note overlap; legato engaged @103 ticks into the first note

    This is why I think it may be a matter of perception. The legato appears to be engaged judging from the appearance of the envelopes, but the gaps that appear between the notes due the truncation introduced by increased latency, cause the notes to sound separated and therefore not as legato.
    Bill

  5. #5

    Re: Latency vs. Legato -- Important read for everyone

    This is fascinating research, thanks Jamie and Bilip.
    I have often felt that the legato layer wasnt engaging on some of the faster runs, but wondered if I was just going stir-crazy.
    I quite often work with very high latency when I am not track laying, so perhaps this explains all.

    regards Joe

  6. #6

    Thumbs up Re: Latency vs. Legato -- Important read for everyone

    Thanks for help with the research, Bill. I think your visuals demonstrate pretty clearly the relationship between legato working and latency. It certainly seems to be able to fail in degrees. The fact that two of the legatos break in an even worse way in the last example is very interesting. It suggests that perhaps the difference between the latency and the controller-to-note-on could have a direct relation to the size of the gap of silence.

    I do still believe that you need my safe "clearance" number to get it to switch. It's just that the further off you are, the uglier things can get!
    - Jamie Kowalski

    All Hands Music - Kowalski on the web
    The Ear Is Always Correct - Writings on composition

  7. #7

    Re: Latency vs. Legato -- Important read for everyone

    I went back and did a more complete job on this, just for fun. I'm glad you raised this issue, Jamie. I've also noticed that legato didn't always sound so legato-ish and now we find that at even medium latencies, the legato feature can deteriorate.

    Bill

  8. #8

    Re: Latency vs. Legato -- Important read for everyone

    Nice work, Bill. Your work might be more helpful if you defined what a "tick" was in your samples. Is that a quarter-note division in your sequencer? If so, I've seen divisions at 240, 480, and 960, and the size of the tick varies with different tempi.
    - Jamie Kowalski

    All Hands Music - Kowalski on the web
    The Ear Is Always Correct - Writings on composition

  9. #9

    Re: Latency vs. Legato -- Important read for everyone

    NV Flute
    Five 16th notes (B5 A5 B5 A5 B5)
    @ 120bpm
    960ticks/quarter
    No note overlap
    Legato engaged @10, 103, and 230 ticks into the first 16th note

    A 16th note is 240 ticks, so the legato is triggered more or less:

    1. Just after the start of the first 16th note (10 ticks in)
    2. In the middle of the first 16th note (103 ticks in)
    3. Just before the end of the first 16th note (230 ticks in)

    Done with SONAR 5 PE
    Athlon 64 3200+
    EMU 1820 soundcard
    Win XP Pro dedicated DAW
    Bill

  10. #10

    Re: Latency vs. Legato -- Important read for everyone

    Ok, we're into math here, so correct me if you see something strange.

    One sixteenth note = 240 ticks = 120 ms

    10 ticks in = 230 ticks before note 2 = 115 ms "clearance"
    103 ticks in = 137 ticks before note 2 = 68 ms clearance
    240 ticks in = 10 ticks before note 2 = 5 ms clearance

    If my original assumption were correct, we would see legato function correctly only where the latency setting is less than the above clearance time. However, it appears that in your tests you had no difference when only the controller placement varied. It could be a direct relation to the length of the previous note.

    We have 120 ms between notes and a partial breakdown at 50ms latency. It looks like we need notes of more than twice the duration of the latency. If I get time, I'll start running some more tests as well. It would be nice to pinpoint exactly what is causing the breakdown.
    - Jamie Kowalski

    All Hands Music - Kowalski on the web
    The Ear Is Always Correct - Writings on composition

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