SAC Plugin Latency Question

Discussions about the use and operation of SAC (Software Audio Console)

SAC Plugin Latency Question

Postby Gil Navarro » Fri May 29, 2015 8:33 am

I've read that SAC won't allow plugins that produce latency. I have some waves plugs that I'd like to use that only produce 1 to 4 samples of latency, like some of the SSL stuff and the NLS Non Linear Summing plug. I don't know much 4 samples of latency is but I'm wondering if it would even cause any phasing issues if it were able to work in SAC? AMP is very very close to meeting all of my primary mixing needs so I'm on the cusp of not using SAC at all anymore, but I'm curious about this latency question.
Thanks.
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Re: SAC Plugin Latency Question

Postby BrentEvans » Fri May 29, 2015 9:48 am

It depends very much upon the type of plug and how much latency you already have. If they're reverbs or delays, you probably won't hear much phasing if you pass only a wet signal. If you're passing dry signal, or trying to do something like parralel compression with a plug like that where you're going to have unprocessed signal mixing with the output of the plug, you'll probably head the phasing.
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Re: SAC Plugin Latency Question

Postby Gil Navarro » Fri May 29, 2015 10:26 am

What I'm wondering is how much latency does it take to get phasing issues?
Example:
Lead vocal processed with an eq or compressor that has 4 samples of latency, then sent to a subgroup with the other vocals. Is 4 samples enough to cause an issue?
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Re: SAC Plugin Latency Question

Postby RBIngraham » Fri May 29, 2015 10:52 am

It depends on many factors. How much bleed from one mic to another, how much other instuments are picked up by the lead vocal, etc, etc, etc... In general, it probably wouldn't be an issue and 4 samples is a very tiny amount of delay. At 44.1 that would be 4/44100s of a second. I will let someone else do the math since I am on a tablet at the moment.

If you folow the 3 to 1 rule and your stage volume isn't out of control it would probably be fine. Easy way to find out... try it and then listen to the difference with a pair of headphones. That is where you most likely notice any difference. Then compare that to what you here in the PA. In the PA you likely wouldn't even notice.
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Re: SAC Plugin Latency Question

Postby jlepore » Fri May 29, 2015 1:18 pm

It wouldn't be a problem unless it met it's unprocessed signal at some point. Then it would.

A moot point anyway since Bob would never allow it (yes, there's third party workarounds, but really .. ).
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Re: SAC Plugin Latency Question

Postby BrentEvans » Fri May 29, 2015 7:44 pm

RBIngraham wrote:At 44.1 that would be 4/44100s of a second. I will let someone else do the math since I am on a tablet at the moment.


.1 ms at 4 samples
So, it's enough to create phasing issues. At 10khz, one cycle takes .1ms. so, for instance you would have significant cancellation at 5khz and 20khz, cycling toward perfect summing at 10khz. At 13.3khz and 6.7khz you'd have about a 90 degree phase angle, which is signal would essentially pass at unity gain.

Now... if you're doing this on outputs going directly to amps... no issue. If you're not blending in pre signal with post signal from this plugs... no issue... but big issue if you blend.

At 1 sample, the key frequency is 40khz, but that doesn't mean it wouldn't be audible, just a bit more complicated to predict.
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Re: SAC Plugin Latency Question

Postby RBIngraham » Fri May 29, 2015 8:41 pm

BrentEvans wrote:
RBIngraham wrote:At 44.1 that would be 4/44100s of a second. I will let someone else do the math since I am on a tablet at the moment.


.1 ms at 4 samples
So, it's enough to create phasing issues. At 10khz, one cycle takes .1ms. so, for instance you would have significant cancellation at 5khz and 20khz, cycling toward perfect summing at 10khz. At 13.3khz and 6.7khz you'd have about a 90 degree phase angle, which is signal would essentially pass at unity gain.

Now... if you're doing this on outputs going directly to amps... no issue. If you're not blending in pre signal with post signal from this plugs... no issue... but big issue if you blend.

At 1 sample, the key frequency is 40khz, but that doesn't mean it wouldn't be audible, just a bit more complicated to predict.


Yeah but in this case it doesn't sound like he is planning on mixing dry and wet signals together. Just processing a mic and then sending it to the outputs. So the only real issue is if there is enough stuff bleading into the processed mic that is not being delayed in an equal manner and then mixed together. But if this is a vocal mic we're talking about, if there is that much bleed in the mic that it's casuing audiable issues... he probably has bigger worries than this 4ms of latency.

But as Joe said.. it's a moot point. SAC doesn't allow a plug in to operate unless it either has no latency or it has to at least report back to the host that it doesn't.

And of course every reverb in the world is basically causing what you're describing. It's just doing it in an artful/pleasent way. :)
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Re: SAC Plugin Latency Question

Postby Gil Navarro » Sat May 30, 2015 7:57 am

Check my math here, but 1ms is a 1/1000 is a second. I'm only talking about 4 samples. At 41k wouldn't that only be 4/41000 of a second? Much less than a ms?
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Re: SAC Plugin Latency Question

Postby BrentEvans » Sat May 30, 2015 9:43 am

Gil Navarro wrote:Check my math here, but 1ms is a 1/1000 is a second. I'm only talking about 4 samples. At 41k wouldn't that only be 4/41000 of a second? Much less than a ms?


Yes. It's roughly 0.1ms, just like I said.
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Re: SAC Plugin Latency Question

Postby Gil Navarro » Sat May 30, 2015 11:53 am

Hey Brent, I didn't see your reply before I posted. Thanks for the info.
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