Understanding Latency Monitor

Hi so I’ve got latency monitor, and I run it and it tells me that my computer is suitable. However I guess I don’t really understand it enough to know how to compare one computer with another. What are the metrics that I should be looking for if I want to make sure I’ve got something that can really handle a heavy VST load going on at once? What is considered good, bad, acceptable , excellent, terrible, etc?

My current computer is not super high-powered and I can definitely choke it if I overload it. I just want to know what to look for if I get a new computer?

What does latency monitor show?
CPU Speed
RAM Speed
Disk Speed
Audio Interface Speed?

A fast SSD Disk
Enough RAM (>= 16GB)
A fast CPU
A good multi client ASIO Interface

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I think you are referring to latencymon?
This tool checks how long it takes for Windows to process items in the Deferred Procedure Calls queue.

Interrupt handling in Windows follows more or less this pattern:

  1. An interrupt occurs (beit a hardware or software interrupt, not completely sure about the last)
  2. The interrupt service routine (resides ‘in’ the os) for the interrupt starts. (Some of the) interrupts are disabled at this point. When it is a trivial job it might process the interrupt, otherwise, it creates a sort of ticket for deferred processing and adds that to the DPC queue. Interrupts are re-enabled
  3. Windows regularly processes all pending ‘tickets’ in the DPC queue

The problem with the DPC queue is, that when there is a ticket with processing that takes a while, all other tickets (including for example an io request for your audio module) after that have to wait. You can compare this to a street with a lot of small cars having to wait while a big truck is trying to pass.
Whether the items in the queue are of a long duration or not depends partially on the quality of the drivers, but ever so often a driver might have to interface with the hardware. Then also the firmware of the hardware gets in the loop. That’s where the hardware including the bios etc can have a lot of impact.

In the past some wifi drivers did the available networks scanning using a DPC. This could easily take 65 ms or more!

All this can lead up to a somewhat paradoxical conclusion: you can have a system with a rather slow cpu, but with drivers (software and firmware) that are very fast. The latency is then really low (but a medium cpu-consuming vst can bring the system to its knees)
It might also be the case that a system has a super duper fast cpu (I9 at lots of GHz’s), but with hardware/firmware that is not optimal. The latency is then very high, while the cpu is almost idling.

It is not possible to predict it. Only experience can tell (more or less). That’s why the list I saw some time ago on this forum is valuable.

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Thanks - what “list” are you referring to exactly?

I saw it recently on this forum, but I must admit that I’ve problems finding it again. I’ll come back to you about it.

I don’t remember whether it was this list or, not, but at least it is something:

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This was the topic, and yes, it was this list:

All - I don’t think I phrased my original question very well, so I’m going to try again. I am NOT trying to analyze my current computer, get general info about what makes a computer better, etc.

Let me try it this way. And perhaps what I’m hoping for is not possible. Let’s say I can try out multiple computers before buying. Let’s say I run Latency Monitor (latencymon) on them. They all might say “suitable for handling real time audio” but I’m assuming, some results are better than others.

Is there ANY WAY to tell from latencymon if my computer is “ok for small loads only” vs “should handle most normal medium complexity set-ups” vs “open 100 vsts at once and it will hardly blink”?

That’s what I’m looking for.

I was merely explaining the way it works, so I agree, my explanation did not answer your question. Sorry

Hey I appreciate your help! And thanks for that latency ranking.

In my opinion it will not:
it depends what you play - many notes, fast slow -
how scripting is involved, what samplerate you are using, what buffer size you are using.
There is no magic software which will tell you how good your machine will be.

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I’m afraid that’s the situation…

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This is an example of the famous “priority inversion” problem in hard real time systems. First identified in the Ph.D. thesis of an old friend of mine many years ago, it refers to the problem where a lower priority task can end up taking precedence over a higher priority task.

Ok - thanks - that might be the only answer.

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latencymon will tell you the longest DPC time. Lower is always better.

It won’t tell you is how much your PC can process in the “remaining” time. The “remaining” time is the time the CPU has to fill the audio buffer minus the time the DPC might take.

All else equal, a faster CPU will be better for a given DPC latency. More cores will also help, but generally less important than clock speed. RAM speed is going to make almost zero difference. “Disk speed” will mostly impact your Gig loading times. Use an SSD, not a spinning disk.

Once you have a system, setting the audio buffer larger will let you run more VSTs before glitching. If you’re trying to keep the buffer size low (to keep latency to a minimum) then the drivers start to matter.

If you’re buying a new laptop, look at that article linked in a prior post. Avoid notebooks on the high side of the list. Once you get into the lower half of the list I think you’re at a point where DPC latency is no longer likely to be your driving factor.

You also have to consider that these are DPC latency measures with a specific set of tests that aren’t generally going to be the same type of activity your PC will be doing while playing music. The worst culprits for high DPC latency in my experience have been network activity and video. The DPC tests in the article include playing a video at 4K resolution and opening 6 web browser tabs. Those are not things I typically expect to do while using GigPerformer, although I will note that the system I’m using right now will audio glitch if I do. I don’t use this system for GP anymore because of that. I found it rather annoying to get audio glitches when I went to guitartabs.com or something like that. Not a problem for live performance, but an irritant for the way I play at home in my leisure time.