HOLMImpulse: Measuring Frequency- & Impulse-Response

[askbojesen]

If:

A[f] = 1/H[f];
C[f] = Conj(H[f])/(Conj(H[f])H[f]+ε[f])

then C[f]=A[f]*B[f], where B[f] is the bandpass function

B[f] = 1/(1+ε[f]/|H[f]H[f]|)

Note that H[f] != 0 for the logsweep
(Also for the 32 bit float or 64 bit double)

[gedlee]

The impulse response data is written out in a form that makes it difficult to read back into another program. This is because it is in two different formats, integer and float on a single line. The integer values of the data are pretty much useless since they just increment by one from one line to the next, so why print them? Just put the starting value and the length in the header and let it go at that. Then just print one float value per line and any program could read in this data.

[KSTR]

Originally posted by askbojesen
Now please don't make this complicated

Seconded! And I really should read up on signal theory, I see!

Without µ[f] we would simply have: C[f] = 1/H[f]
Applying µ[f] is nothing else than a bandpass of the resulting response. Like when Klaus is sweeping from 1000 Hz, then he knows that the response below 1000 Hz is not valid.

That bandpass functionality is already there, for the result, in the options dialog, right?

I'm in doubt if I should adopt this bandpass for the log-sweep - If I did Klaus and Earl would require that it could be disabled, so they could get the raw impulse

From the practical standpoint this might nevertheless be a good idea, HF-limiting the stimulus (LF we have already). Like when I use high sample rates (96k++) to lessen the burden for both the DUT(+amplifier) and the imperfect ADC/DAC-chain, measuring DUTs with higher distortion ... but I better leave that decision to others/you, I think.

- Klaus

[askbojesen]

Version 1.1.5.0 (2009-06-09)

http://www.holmacoustics.com/holmimpulse.php

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

Features/Changes:
* File type *.hlm registered for HOLMImpulse (Double-click on file.hlm)
* Impulse-Graph improved graphics (Peak-To-Peak)
* Export impulse response: Sample number is optional (CheckBox)
* Max signal Length = 20 (Was 21, but crashed need to troubleshoot)
* New Icons

Bugfixes:
* Post-Time window to small (Increased by x10)
* Impulse-Graph x-axis-label postition
* Harmonic distortion: Only plotting at frequencies where data is available

Issues
http://www.holmacoustics.com/downloa...lse/Issues.txt

[KSTR]

^^^Now that was quick! Thanks!

[JohnPM]

Originally posted by askbojesen
I'm in doubt if I should adopt this bandpass for the log-sweep - If I did Klaus and Earl would require that it could be disabled, so they could get the raw impulse

If you don't do this (or something similar ) on a band-limited sweep then noise gets boosted where the stimulus energy is low and the quality of the impulse response can be severely degraded, it doesn't take a lot of LF noise to greatly change the appearance of the IR.

[askbojesen]

Originally posted by doug20
How about a HOLM for Dummies? (Me, I feel dummer by the day on this site!!).
I do not want to bog down this thread with really silly and probably easy to answer questions, could we create a HOLM for dummies thread?

Well now, I believe you are right, so I have started a new thread:

HOLMImpulse: Measurements in practice
http://www.diyaudio.com/forums/showthread.php?s=&postid=1851460


Now we will see if this new thread gets a life...

[askbojesen]

HOLMImpulse: Measurements in practice

HOLMImpulse: Measurements in practice


sorry

[David_Web]

Thought this fitted better here instead of the other thread.

Any way to disable auto detection?
The reflected sound when doing measurements close up will not affect things that much, and it is very annoying to disable it after every measurement.
If you measure at 80dB at 30cm and the closest reflection is at 1m.
The reflected sound will be -16.5dB down. That will add 0.1dB to the total sound. Well I'm not that good at sound theory so it might be wrong but still. When you want to see a trend in response ungated is needed.

Hmm. Any way to use a rollof for gating? Remove the HF part of the reflection and then leave the LF part to not mess up the shape of the response.

A little checkbox would be nice. I looked at everything but I could not find one. Sorry if I missed it.


Any news on IR export to wave?

[KSTR]

Suggestion for an additional display feature (say, for version 2.xxx), Arsinh scaling:
A novel mapping with natural transition from linear to logarithmic scaling

- Klaus