HOLMImpulse: Measurements in practice

[Key]

Thanks for the help!

Well yeah it was a bit of a selfish experiment I admit haha. But you see if I could somehow put an allpass at key pressue points to somewhat linearize the output of my speakers this might help me "see into the recordings" better and therefore help me mix the song better. I could always take the de-emphasis out of the chain before the final mixdown/render.

The more I think about the idea the more it makes no sense in a real world haha. But it's one of those things I have seen people talk about trying with DSP that was not exactly possible without a great deal of effort and loss with analog means.

I have some maliable all pass dsp that I can mess around with and actually try the concept out. Most experiments that I have read about where they attempt this the results seem to prove that phase linearity is actually negligble at a certain point and that phase relationship of the drivers despite the linearity of the group delay is what is really important. I guess I was attempting to prove this to myself one way or the other.

[Ferrit37]

Hey Key,
This might be of some interest to you, Gunness Focus

http://www.eaw.com/info/EAW/Technica...Whitepaper.pdf

and this: http://www.eaw.com/technology/propri...nnessFocusing/

[Key]

Read the first one thanks. De ja vu though I may have read that one before but I think I read it more for the phase plug stuff the first time. Still helpful. Will have to take a look at the other one.
Thanks Ferrit37

[Key]

Okay so this is the closest I could get with my clunky improvised all-pass network.
http://img12.imageshack.us/i/spectruma.png/

It's like a rubix cube trying to get that crazy steep slope on both sides of the crossover with the network I am using.

I thought I was hearing a slightly extended transient response at first. I tried to ABX the two different versions twice and failed. Both times though on the first two choices I could hear the difference and the ABX said I got the answer correct. But both times by the time I got to the 3rd try with ABXing it became very difficult to distinguish a difference between the two and would resort to guessing and getting it wrong.

I would think that even though the filter is obviously not a perfect match for my crossover that I should still be able to tell a difference. But I will keep this idea in the back of my head until I come across a better convolution solution to maybe import the inverse impulse response into a VST. At this point it seems like it doesn't really make much of a difference from my perspective.

[Ferrit37]

Hey Key,
Here's a screenshot of a measurement of 6 x KF730 line array modules flown under 2 x SB730 at about 35 feet trim, measured about 50 feet back.
The top trace is the Phase response, the bottom trace is Magnitude, (red trace is coherence).

The interesting thing is Gunness focus has been applied from about 250Hz and up to limit latency and there is a passive crossover between the MF/HF around 1200Hz but the phase response is reasonably flat.

[IMG]<a href="http://s643.photobucket.com/albums/uu160/Ferrit37/?action=view&current=730.jpg" target="_blank"><img src="http://i643.photobucket.com/albums/uu160/Ferrit37/730.jpg" border="0" alt="730"></a>[/IMG]

[Key]

Yeah I am still kinda new to the impulse response thing so I don't know how to make an inverse all pass that closely matches my speakers and it's active crossover. I think I know some development tools for VST which might work but I have to buy them first.

I cheated a little and just ran the file through the all-pass in reverse for one of the steps so there wasn't a way I could just take the measurement of the whole chain in real time. That last pic was just the all-pass phase de-emphasis isolated and not added into the actual speakers' crossover.

I assume the curve should look a lot like Guness's logo where you have that vertical slope on the crossover point. This seemed to be beyond what I was capable of doing with my adjustable all-pass. I think the best I could hope for was an approximate slope around the 1.8kHz range. I was doing it all with trial and error so I couldn't tweak the filters in real time either. So yeah a lot of things working against me to where I basically need a better method or tools to properly experiment with the idea.

It just seemed like there was some shift though and that my brain was working to make the regular file match the one that had the phase de-emphasis or vice versa. But yeah I should do the experiment better before reaching any conclusions.

[Ferrit37]

Hey Key,
You might want to look into Convolution techniques, for instance Gratisvolver at: http://www.catt.se/download_area.htm (Scroll down) and there's a bunch of VST implementations out there.
If you get a good impulse response of your Speakers you could do an inverse.

[Key]

Thanks Ferrit37!

Downloaded it but haven't had a chance to mess with it yet.

[Ferrit37]

Hey Key,
Pat Brown at SYN-AUD-CON posted some interesting stuff on convolution let me know I could PM them.

[Key]

Cool, GO ahead and send them when you get a chance. I'm not doing anything. Thanks