Something Cool I've Been Working On

Interesting comment of Jay Mitchell on the Gear Page on this subject

"Cliff is mistaking mathematical artifacts for acoustic ones. It's a very common mistake but a mistake nonetheless."

Here's the link:

The Gear Page - View Single Post - Future IR Technology from Fractalaudio?

There are obviously some intelligent people voicing opinions here. Unfortunately, intelligence is often accompanied by a defensive, " if I didn't think of it, it can't be right!", attitude.
I see it this way, I purchased the Axe II with FW5, and thought it was better than anything I'd ever played through. Now, with FW11, the improvements are nothing short of astonishing! With every FW, tweaks and advancements have made a product I thought couldn't get much better, get much better every time.
This isn't a lemming or fanboy response, just an honest assessment of the Axe II.
I don't care about the negativity, or pissing and moaning others do. I only care about the end result.
I know that Cliff and Fractal have demonstrated time and time again, that passion, dedication, and a willingness to think outside the box produces results that give me better tone.
I'll follow Cliff down any rabbit hole he wants to explore at this point.
He's earned my trust, because so far, trusting him has made my Strat sing!

Jay is an intelligent guy, but he should look at the technology and innovation that Cliff has introduced.

Whether he understands Cliff's idea, disagrees with it or whatever, he should let it play out, and give Cliff the respect he's earned.

IMHO, YMMV, etc....


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Yes, that's exactly the way to look at it. The problem is that human perception is logarithmic and IRs are a linear process. 48 Hz resolution is way more than necessary at, say, a few kHz but not nearly enough at low frequencies. The brute force solution is to use very long IRs, 8K or more. UltraRes solves this in a novel way that uses little to no extra processing power and no additional latency.

So you are basically using an adaptive technique that trades off higher frequency resolution for lower frequency resolution; I'm assuming you distribute the resolution non-linearly (logarithmically per octave maybe?). I'm not sure where the novel part comes from though, there's even a patent from the early 90's that describes similar behavior.
 
This is too cool! And Exiting! Can't wait to try it! I've thought the longer IR's were more detailed and accurate for quite some time, but kept my thoughts to myself for the most part because of the disagreements over this subject.
Cliff , you ROCK!!!
 
Windowing only smooths the response even more. This is basic FFT theory. The less time-domain information you have, the less frequency domain information you have and vice-versa. This is the uncertainty principle. I always window IRs with a Hann window.

@Cliff: I never use windows (i.e. I use a rectangular window, but no Hann, Hamming, etc.) due to following consideration:
Assume a sinusoidal signal with a freq. of 10Hz and an amplitude of 1.
When this signal is windowed with a 1 sec long rectangular window then the FFT will show a peak at 10Hz with an amplitude of 1. If a Hann window is applied the amplitude of the peak at 10Hz will be around 0.5.
How do you cope with this difference?
 
@Cliff: I never use windows (i.e. I use a rectangular window, but no Hann, Hamming, etc.) due to following consideration:
Assume a sinusoidal signal with a freq. of 10Hz and an amplitude of 1.
When this signal is windowed with a 1 sec long rectangular window then the FFT will show a peak at 10Hz with an amplitude of 1. If a Hann window is applied the amplitude of the peak at 10Hz will be around 0.5.
How do you cope with this difference?

Normalization is your friend. Rectangular windows are simply truncation and are generally regarded as bad practice due to extremely high sidelobe levels. The choice of window is subjective. I actually use my own custom window that is not really a Hann window but that's proprietary information. My window preserves more frequency detail while still suppressing Gibbs phenomenon. Windowing trades off frequency resolution for sidelobe suppression. My window is optimized for the unique statistics of IRs. For a random process I tend towards Bessel-Kaiser windows. IRs have unique statistics that aren't addressed by any of the standard textbook windows.
 
Normalization is your friend. Rectangular windows are simply truncation and are generally regarded as bad practice due to extremely high sidelobe levels. The choice of window is subjective. I actually use my own custom window that is not really a Hann window but that's proprietary information. My window preserves more frequency detail while still suppressing Gibbs phenomenon. Windowing trades off frequency resolution for sidelobe suppression. My window is optimized for the unique statistics of IRs. For a random process I tend towards Bessel-Kaiser windows. IRs have unique statistics that aren't addressed by any of the standard textbook windows.

Turns me on when I hear dirty talk like that!
 
Whenever I am feeling too smart for my own good I just check in to one of these discussions and instantly come back out humbled again. I have no idea how it is going to work but what my little brain is hearing is that the IR's will be better and for that I thank you.
 
It's not a mathematical mistake and nothing to do with windowing.

That peak in the bass response might be the speaker, it might be the room. Looking at the actual IR it appears to be the speaker as there are no discernible early reflections.

The frequency resolution of an IR is the sample rate divided by the number of samples in the IR. The window function has nothing to do with frequency resolution (except for making it even less). So a 1K IR at 48 kHz sample rate has a frequency resolution of roughly 48 Hz. If a speaker has a resonance (formant) at, say 80 Hz with a Q of, say, 3.0, then 48 Hz is insufficient to capture that resonance accurately. You need a frequency resolution of several Hz to accurately recreate that resonance. I chose 80 Hz and a Q of 3 because that's what that response looks like. The Q could even be higher than that.

It doesn't take much mental energy to realize that if you have a narrow formant at a low frequency then you need fine frequency resolution to reproduce that. An 80 Hz formant with a Q of 3 only spans about 25 Hz. Obviously a frequency resolution of 48 Hz is not going to be able to reproduce that.

Windowing only smooths the response even more. This is basic FFT theory. The less time-domain information you have, the less frequency domain information you have and vice-versa. This is the uncertainty principle. I always window IRs with a Hann window.

EDIT: I broke out my impedance measurements for that Vox cabinet and the speaker resonance is 80 Hz.

@ Cliff: I'm just wondering what you think about the resoance at around 35-40Hz. Could that be due to a room mode?
 
ITT:

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:D Can't wait to try the new IRs!
 
I think this sounds awesome and if Cliff says its better I believe him. I only hope when the Fractal cab utility is released we can blend our current ir's with the new format ir's , possibilities........ :)
 
FWIW, I like the sound of my RedWirez IR mix cut at 24ms as anything longer had too much room in it.
 
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