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Author Topic: Smaart Delay Finder questions?  (Read 7844 times)

Peter Morris

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Re: Smaart Delay Finder questions?
« Reply #10 on: January 20, 2016, 08:25:17 pm »

Thx Peter,  the idea of aligning first arrivals via phase trace is getting more and more clear.
 
Phase alignment is what i have been trying to do all along, but i also want to understand how delay finder works, and what the terms such group delay, minimum phase, etc, all mean.

I can grasp that group delay is the derivative with respect to frequency, i was just have trouble picturing 'derivative at what frequency or frequency interval'.
Here's a pretty good link i found on that ...http://na.support.keysight.com/pxi/help/latest/Tutorials/Group_Delay6_5.htm

If you or others have further reading you've found that helps...much appreciated !!!!

Here is an example of the phase and group delay using a reflex speaker plot.

Have a look a the phase plot at 100Hz - draw a line tangent to it (red line) - its slope will be the derivative. 

Group delay is the -ve first derivative of phase.

Measure the slope/gradient using the points where the line intercepts 0 degrees and 180 degrees

This gives you a gradient of  .... 180 degrees / 280Hz - 18Hz =  180 degrees /262Hz

Now one cycle = 360 degrees so the equation becomes 180 degrees /(262 *360 degrees)/sec = 0.0019s or 1.9ms

i.e. the group delay @ 100Hz = 1.9ms ... Refer group delay plot at 100Hz = 1.9ms.

Note: be careful once you have phase wrap 
http://www.cjs-labs.com/sitebuildercontent/sitebuilderfiles/GroupDelay.pdf
« Last Edit: January 21, 2016, 09:50:52 am by Peter Morris »
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Mark Wilkinson

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Re: Smaart Delay Finder questions?
« Reply #11 on: January 22, 2016, 01:08:54 pm »

Here is an example of the phase and group delay using a reflex speaker plot.

Have a look a the phase plot at 100Hz - draw a line tangent to it (red line) - its slope will be the derivative. 

Group delay is the -ve first derivative of phase.

Measure the slope/gradient using the points where the line intercepts 0 degrees and 180 degrees

This gives you a gradient of  .... 180 degrees / 280Hz - 18Hz =  180 degrees /262Hz

Now one cycle = 360 degrees so the equation becomes 180 degrees /(262 *360 degrees)/sec = 0.0019s or 1.9ms

i.e. the group delay @ 100Hz = 1.9ms ... Refer group delay plot at 100Hz = 1.9ms.

Note: be careful once you have phase wrap 
http://www.cjs-labs.com/sitebuildercontent/sitebuilderfiles/GroupDelay.pdf

Peter, very helpful, many thanks!
Your example is very clear, and great link too..

The warning about phase wrap is half the reason I've been interested in how smaarts delay finder works....to understand how to use the delay finder and also make sure I get phase fully unwrapped


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ProSoundWeb Community

Re: Smaart Delay Finder questions?
« Reply #11 on: January 22, 2016, 01:08:54 pm »


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