Why Do We Have Latency?

[GTLazer]

More of a computery question, really, but I'm sure some of you will be able to help...

 

I understand what latency is and, for the most part, what causes it, but why do we have it?

 

For example, my HD 500 is quite happy to do A/D and D/A with a whole bunch of amp modelling and FX processing in between and with no latency, whereas my decent-spec laptop can't do anything without adding latency delay.

 

What's the difference? Why do computers always introduce latency?

[jandrio]

[joel_brown]

General purpose OS and CPU versus Realtime OS and very specific CPU.  It's like asking why my Toyota Camry doesn't go as fast as a Ferrari.  But try taking the Ferrai to the grocery store then taking your kids to soccer practice.

[Charlie_Watt]

The HD500 has latency - just not enough to notice.  It is designed to do Audio processing with minimum of latency.  A PC isn't designed to do real time processing - it's actually not very good at that.

[innovine]

What latency do you get from your laptop? It depends heavily on the drivers, and you can probably get below 10ms with the right setup. The latency is caused by many reasons, one main one is that the cpu is often needed for other tasks. So audio processing is suspended while the cpu goes and works on something else like your antivirus or drawing the screen or whatever. During this time, your soundcard is still receiving (and/or transmitting audio). the driver sets up a little buffer with the next few miliseconds of audio in it, so when the cpu is busy, you .on't run out of audio data to process. Then after a while the cpu gets back to dealing with your daw, and refills the buffer, and goes off to do other tasks again. Latency and this buffer are very closely linked. A small buffer means a smaller delay, but when it gets too low the buffer will empty before the cpu gets a chance to add more data, producing very nasty tearing and popping noises. You of course need such a buffer on the input (queue up incoming audio until cpu can deal with it) and on the output.

The OS is demanding enough, and general purpose enough so that the latency is noticable. Dedicated machines aren't dealing with a webbrowser or a usb bus or a wireless network or hard drive and hundreds more background tasks, meaning that there is much less competition for resources (though it is still there). The latency is low, but still there, only analog signal paths are latency free. The voltage in the analog signal chain rises and falls basically instantly through the whole signal chain, but digital gear has queues and buffers in many many places. Zero latency is impossible, just standing 2m from your speakers add ~6ms for the sound to travel to your ear. But if your fancy laptop is saying the latency is several times that, then you can probably adjust it down

[GTLazer]

These are all excellent answers, thank you. +1 for you all.

[spaceatl]

Well, once we get Quantum Computers working, then we will hear what we played before we played it and have the opposite problem.  :blink:

[joel_brown]

But just by observing the tone, it will change it.

[innovine]

Instead of dialing in your tone, you get all of them at once.

[bignath]

New product line.......The Line6 Delorian.

[panaman]

one thing Creamware recommends for their dsp pci cards is to switch off hyperthreading on the pc cpu.

while HT may be great for bit crunching tasks, where one algorhythm is applied to generate a fractal, convert video or whatever, it may introduce latency on the audio signal.

also make sure the cpu/energy settings are configured for optimal performance, not for optimal battery life, where cpu and bus are clocked down for energy saving.

disable all unused hardware like wlan, parallel and serial bus, webcams, firewire, touchscreen, cardreaders  in the bios, not in system-hardware.

try getting asio drivers for Your sound chip.

try a lower resolution (800x600 rather than full hd)

latency happens both on the input and output paths, try monitoring the pc input rather than the output, splitting up Your signal before it goes to pc. its a compromise, but will give You an instant response of your playing, the wet signal from pc can then be mixed in. (some effects take some time to build up anyway).

[cweeklund]

GTLaser - is your newer laptop using a 64-bit OS?  I had a really crappy laptop and recently  moved to a considerably newer one, and the latency is considerably more with the newer laptop.  I haven't tried to reinstall a 32-bit OS, but am wondering if the 64-bit-ness of my newer one is part of the issue.  I'm sure it could be the USB ports/drivers as well.

[rmaginnis]

I may not be on the right topic but maybe someone can guide me? I ran my laptop through the hd500 and then to my amp. My problem is this , when i play a song through Widows Media Player to the HD500 the sound /songs seem to stutter . Any ideas why this is happening?

[Charlie_Watt]

I do this by using the Headphone output into the CD Player input.  Works fine.  I wouldn't use with USB while also running Line6Edit