Why not IMD curves?

[GOULAS]

Hello friends.

I saw this. It was done a long time ago. Why could not we do the same measurements?

https://legacy.renkus-heinz.com/downloads/Loudspeaker_Components/Classic_RH_Drivers/SSD1801_data.pdf

 

[John Mulcahy]

Log sweep measurements can only discriminate harmonic distortion. FSAF measurements can determine total distortion, which is mainly the sum of harmonic and intermodulation distortion. Stepped measurements allow a choice of various fixed frequency IMD measures vs signal level. The graph image you showed would require a sort of IMD sweep, a two tone signal with a fixed offset between the tones and suitably synchronised processing of the captured signal to extract the IMD components.

 

[GOULAS]

Thank you, Mr. John. Don't you find these curves interesting? Since they are old IMD curves, I thought it might be possible to reproduce them today. Instead of harmonic distortions, which aren't representative of transients, perhaps you could offer us these curves from a new program, based on the two tones? In my opinion, this is a lead worth exploring. You and REW would then be the first to present an updated measurement. Only you could do that!

 

[dcibel]

FWIW This was discussed back in April 2024, here:

D

Thread 'Multitone distortion chart'

Apr 3, 2024

Hello,
More of a general inquiry / feature request. I am wondering if there is any plan to add a multitone distortion plot, similar to what Klippel shows here:

Multi-tone Distortion

www.klippel.de

Most of the functionality already exists in REW through the generator and RTA functions, I would think it's just a matter of integrating between the peaks of a multitone measurement to create the chart.

• dcibel
• Replies: 8
• Forum: Official REW (Room EQ Wizard) Support Forum

The above discussion occurred prior to REW incorporating FSAF, and REW is the first software to incorporate FSAF beyond it's original development in MATLAB. My thoughts today is that FSAF represents the modern advancement in audio distortion analysis, as time goes on we may see these individual IMD measurement or sweep become an "old, outdated, obsolete" method of analysis. It's time we start analysing audio with audio instead of synthetic tones