Sample rate and SIR CPU Hit

[jamie_drum]

I was just reading the Sound on Sound article about freeware music on the web.
The author mentions he used SIR at 44.1 KHz and it only took about a 4% of CPU with a system not dissimilar to my own (a P4 2.54 GHz and I have 768 RAM). I thought to myself--that seems a lot better than I am getting.

So I tried it out. If I use SIR at 16/44.1KHz I use about 5-8% CPU, but when I use it at 24/96 I am using over 20% CPU, with spikes of 40-50%! This is just sending two audio tracks to a single instance of SIR on an effects bus.

Is this normal performance? Does the sampling rate and bit depth affect the CPU usage that much? I looked at a few other plugins and the difference didn't seem nearly as great.

[moskus]

The CPU usage of SIR is dependent of the Impulse Response you use. The higher quality and length of the IR, the heavier CPU-load.

[jamie_drum]

Originally Posted by moskus

The CPU usage of SIR is dependent of the Impulse Response you use. The higher quality and length of the IR, the heavier CPU-load.

OK, I follow you. However, would the sample rate still make a difference? For instance, if I am using a 44.1 KHz impulse response, but the project is at 24/96, would that require more CPU than using the same IR at 16/44? I guess it must, but is the conversion responsible for the heavy CPU usage I am seeing? Would I be better off getting an IR at 24/96 for any projects at that bit rate and sample depth?

[moskus]

I haven't tested this (I only use 44.1 kHz), but in theory the samplerate and bitrate would make a difference on the CPU-load.

SIR uses convolution to make it's smooth reverb. For each sample in the IR, it will add the original sound... (well, this was poorly explaind). But when the bitrate and samplerate is rised, then the number of calculations is raised too.

[Qwerty]

See - jamie_drum, you now have the perfect excuse to use on your significant other as to why you DESPERATELY MUST HAVE the new 'Freeze' function only available in Sonar 4!

SIR is a dog on the CPU, but it's free and sounds nice so I just pat it on the head and baby it along... If the dude really does release his 'zero latency' version as a commercial product, (as he talks about on his website), then I will start getting antsy about this stuff.

Ciao,

Q.