HOLMImpulse: Measurements in practice

[askbojesen]

Hi Schauki an Klaus

Originally posted by KSTR
I had mentioned this also (in the other thread), seems to be related to screen resolution and/or a user specified font size...

(see attachment)

I tried a 120 dpi screen resolution and got the same problem as you. I beleive it is fixed now:

http://www.holmacoustics.com/downloa.../ChangeLog.txt

Version 1.1.5.4 (2009-06-13)
Bugfixes:
* DPI resolution other than 96 in Windows setting
* Improved scaling when using large fonts in Windows setting

Have a nice weekend!
I won't be here more this weekend

[KSTR]

Great, you fixed it, thanks!

[askbojesen]

Originally posted by panomaniac
My current setup is:
USB>M-Audio Duo>Spdif>DCX2496>amp>speaker
I calibrated the M-Audio card with line out patched back to line in. Very flat. But I think I need to go thru the DCX (all filters off- delays on) and into the mic input of the M-Audio (padded) to get a really good cal. Or do delays make any difference?
What do you think?

It could be very interesting to see the response of the outputs of the DCX2496 with your x-overs:

USB>M-Audio>Spdif>DCX2496->Analog->M-Audio

I mean you can direct verify the LP/HP/BP of the DCX2496
It is interesting to see the phase/impulse of the LP/HP/BP.
(Then you know what phase is from the DCX2496 and what is from your speaker)

If you want to calibrate (also for speaker mesurements) then I believe you should set DCX2496 in allpass mode and measure.

Waiting in excitement for you x-over response images

[Pano]

OK, good idea!

I have a few days of heavy video work ahead of me, but will try to takes some measurements in the evenings. Will post here.

[Pano]

I had a quick try at this - but got wierd results. LP filter was OK, HP very strange.

How should I post here? Just graphs - or can I export something and put it here for you?

Also, if I do a loop back calibration of the soundcard, then run a measurement of the sound card, shouldn't the measurement show flat? Shouldn't the calibration file cancel out any FR or phase errors? I don't see this happening in my measurements.

[askbojesen]

Originally posted by panomaniac
I had a quick try at this - but got wierd results. LP filter was OK, HP very strange.
How should I post here? Just graphs - or can I export something and put it here for you?

I think frequency- & Impulse-response graphs: File > "Save Frequency- & Impulse-Response
You have zoomed so we can see the impulse-response (The time window is not important when not making acoustic measurements, except, that it should be long enough)
Plot both gain and phase (not THD)

Remember then to give the measurement slots some names before saving the image. Legends will be written to the file.png when saved.

If something is really weird, then you can sent the measurement file (file.hlm) to support@holmacoustics.com, so I can load the file myself.

[Pano]

Here are 3 measurements for you.
Signal path = USB>M-Audio Duo>Spdif>DCX-M-Audio>USB

Calibrated on analog loop, but digital thru the DCX looks almost identical. tiny phase shift in the low end between analog and digital.

Here are some sample filters from a stock DCX2496. All from same channel (2). All at 1KHz.

First order below.

[Pano]

Here is Butterworth 18dB. Note dip caused by phase inversion.

[Pano]

And last a Linkwitz-Riley 48dB/octave

[askbojesen]

Thanks for the measurements

I see that Impulse peak time = 0 detect does not work for these IIR filters (I mostly tested on raw drivers or linear phase FIR)

From Measurement options you can adjust the time offset manually.

Two changes I'll implement to improve above measurements:
[list=1][*]I'll change the time = 0 strategy to a simple peak detect.[*]It would also be appropriate to disable gain normalization
(This is already a feature request)[/list=1]

I'll be back