Something Cool I've Been Working On

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FractalAudio

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The problem with conventional IRs is that they are too short to capture the detail in the low frequencies. There are those that maintain 20 ms is the maximum length you need to fully replicate the speaker. This would be about 1000 samples at 48 kHz.

I disagree with this as I have many IRs here that exhibit significant energy beyond 20 ms. I believe the room has some influence as the low-frequency modes of the room will impact the resulting sound. The amount of this impact depends on the room, the mics, distance, etc., etc. Or perhaps certain speakers have particularly high Qs in the low frequencies. Regardless, it is my opinion that you need IRs much longer than 20 ms to fully capture the "mic'd amp in the studio" sound.

My tests show that IRs of 8000 samples are required to fully capture the low-frequency detail. Unfortunately to process an 8K IR in real-time require copious processing power...

Fortunately I have developed "UltraRes (TM)" cabinet modeling. UltraRes cabinet modeling provides the frequency detail of a very long IR with little or no added processing power requirements.

The following image depicts the response of UltraRes cabinet IR processing:
The blue trace is the frequency response of the original (long) IR. It is a Vox AC-30 cab.
The green trace is the frequency response of the same IR truncated to 1K samples. This is "normal resolution" in the Axe-Fx and 2-4 times longer than what other products use.
The red trace is the frequency response using UltraRes processing.

I’ve shifted each trace by 0.5 dB to make comparison easier.

ultra_res.jpg
 
So what would be the biggest audible difference with these IR's as opposed to the conventional smaller-sample IR? Would it mainly just be in the lower frequencies?
 
Progress is always cool Cliff! Does this make all the existing IRs useless or are they infact longer but simply not used for more than 20ms? There sure is happening a lot of stuff after 20ms when shooting IRs. You can at least see it in the waveform.
 
RedWirez guy told me that everything beyond 24ms in his IRs are room reflections, starting with the ceiling. Apparently the floor is not a factor with close mic'ed IRs.
 
And also one reason I still shoot my IRs with Voxengo is that I think a longer/slower sine wave gives me a more accurate low end and definition. The Axe-Fx inbuilt IR capture quick sines give me a very soft rounded IR in comparison. Have you experimented with this also?
 
judging from the waveforms, i would think that it would be an audible difference......enough to make the move to UltraRes IR's without question. sometimes, close-enough is just not close enough.
 
Clark Kent said:
Progress is always cool Cliff! Does this make all the existing IRs useless or are they infact longer but simply not used for more than 20ms? There sure is happening a lot of stuff after 20ms when shooting IRs. You can at least see it in the waveform.
Click to expand...

Existing IRs will still be processed as usual. UltraRes IRs will be tagged as such which will indicate to the processor to use the new processing algorithms. Note that UltraRes IR data is not conventional IR data.
 
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