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 Forum index » How-tos » Ambiophonic Sound Reproduction
CPU Usage oddity
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Shike



Joined: Dec 31, 2014
Posts: 4
Location: US

PostPosted: Sun Apr 10, 2016 1:40 pm    Post subject: CPU Usage oddity Reply with quote  Mark this post and the followings unread

Greetings,

When using AmbiophonicDSP I noticed an odd issue. If you are not feeding it any sound the CPU usage can skyrocket (from 7% utilization to 30% easy).

The only way I have found around this thus far is to feed a test signal at -191dB to both inputs of the DSP. Seems like when no sound is fed the DSP goes crazy?

I'm not too concerned since I did find a workaround and my application is largely overkill, but thought it was worth bringing up in the hopes that it may eventually get fixed.
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HrastProgrammer



Joined: Oct 16, 2008
Posts: 289
Location: CPU
Audio files: 64

PostPosted: Sat Apr 16, 2016 10:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't own this plugin, so I am just guessing, but it is most likely a denormals problem.

To the developers ...

If you are using SSE instructions then enable FTZ (Flush To Zero) and DAZ (Denormals are Zero) CPU flags:

https://software.intel.com/en-us/node/513376

Or just mix a small amount of white noise (below -120dB) at appropriate stages inside a signal chain - input, output, etc.

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mosc
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Joined: Jan 31, 2003
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PostPosted: Mon Apr 18, 2016 9:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for both posts. I'm on the verge of doing a complete rewrite of this plugin so it will run on both OSX and Windows.

I was unable to duplicate this CPU load on my machine. I wonder if there is something going on with particular VST hosts, or OS versions.

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HrastProgrammer



Joined: Oct 16, 2008
Posts: 289
Location: CPU
Audio files: 64

PostPosted: Mon Apr 18, 2016 9:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, it could be VST host related. I stumbled upon denormals problem during the development of my Tranzistow synthesizer. So, I turned on DAZ/FTZ flags (because my audio processing code is mostly SSE3 assembler) and mixed some very low amplitude white noise at the output stage, just in case. This is very cheap operation and couldn't hurt anything ...
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