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Old 11-21-2021, 01:34 PM
Cuki79 Cuki79 is offline
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Default IR experiments - Wetness, distant feel problem

Hi everyone,

Today I did a new signal processing experiment.

Here is the problem I want to address:

IR convolution (also known as FIR filtering) although enabling to have great mic-like tone sometimes lead to a "distant" or "wet" feel.

The problem comes from the fact tha IR convolution basically behaves as a "reverb", it adds a "reverb tail" to everything you play.

Contrary to reverb, the tail is very shot. Typically ~40ms (2000 pts IR).

If you look carefully at an IR file, it looks like that

The horizontal axis is time. You can clearly see it start as an impulse that damps in time forming a "tail".

The good: The tail actually accounts for the top reacting to the pluck. So it will feel more realistic compared to a dry undersaddle sound that feels very "direct".
The bad: In order to have good accuracy in the low frequency, the tail must be long... The result is a "wet"/"distant" feeling.

That is why from the very begining, Larry Fishman had the low end handled by biquad IIR filters (EQ). with the benefit that shorter IR convolution/FIR filter requires less DSP power.

So today experiment is too have most of the job done by EQ (IIR biquad filters) and just add a "touch" of IR convolution (FIR filtering) to add that "sens/feel" of top response.

The setup is shown below

* I use an Undersaddle transducer (Fishman Matrix)

* An Axoloti board in which I programmed a Highpass filter and 6 parametric EQs based on a FabFilter Pro Q EQ curve. Fabfilter Pro Q is a plugin that automatically compute an EQ curve to match two tracks. In this case, the plug-in tried to match the pickup with a SM57 take.

* After the EQ, I added a custom made IR convolution of only 64 pts (1.3ms). This very short. For example, on my website defaults IRs are 2048 pts (42ms). With such a short IR, there is no "wet/distant" feeling.
The IR is build to be mostly transparent. It's a straight impulse + a touch of noise above 900Hz.

Why did I do that?
1) The EQ curves basically models the low frequency resonant modes of the top.
2) At higher frequencies, there are so many modes, you can't model them with EQ... In this case random noise is actually a good approximation.
3) How will it affect to the sound? The big impulse at the begining, represents the unaffected tone. It's where most of the energy sits. the super low noisy tail means I am spreading some of the high end over 1.3ms. It means that all the high frequencies are not only dedicated to build the fast/sharp transient of the pluck attack but also to model the fast oscillations from the guitar top (however to a minor degree).
If you watch the last figure on the bottom right, one can see, the IR file does nearly no correction in the spectrum domain. It will just spread some of the high frequency over 1.3 ms.

Does it work? > I think it does

Can you hear it on a recording? > Probably not. (as I said the spectrum response is barely affected)

So why all the fuss?
Because when you play the guitar plugged in, you have that "soft touch response" without getting the distant feel.


1) 100% pickup
2) Pickup + EQ
3) Pickup + EQ + IR made of Impulse + noise above 900Hz

My 2 cents,
Cuki

PS: The goal in this experiment is NOT to get a mic-like tone. It's to get a dry, plugged-in tone with a "good feel" and less to no quack.
PS2: Such process is less demanding computing wise than Hard 2048pts IR convolution. It could be done with cheap pedals and probably even with onboard electronics. The whole process + footwsitch uses 14% of the Axoloti computing power. 1024pts IR in comparison alone uses 74% of the computing power. We are very very far from Tonedexter or HX stomp processing power.
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Last edited by Cuki79; 11-21-2021 at 01:46 PM.
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  #2  
Old 11-21-2021, 02:23 PM
SpruceTop SpruceTop is offline
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Thanks, Cuki! I prefer 3) Pickup + EQ + IR made of Impulse + noise above 900Hz. One of the reasons I used effects very sparingly was because they added that "distant" tone and feel to the amplified guitar tone. This would be especially noticeable as a solo act when stepping on a pedal to add an effect during a song. Although I played around with chorus, reverb, and delay on guitar, and used the MXR Pitch Transposer for a while for harmony on some vocals. I played mainly "bareback" back in the day, and if anything I used a little reverb on only my vocals.
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Last edited by SpruceTop; 11-22-2021 at 04:25 AM.
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Old 11-21-2021, 03:45 PM
jonfields45 jonfields45 is offline
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3 > 2 >1. I'm surprised that what I thought I heard I might not attribute to higher frequency tweaking that #3 presumably has over #2.

But I do think the IRs we've generated (no IIR), even at 2K points, are a better sounding solution than an Aura pedal with the nearest, even exact guitar and PuP, download from Fishman. However, not a test I did in any fair manner, just my recollection from owning several Aura pedals over the years.

I also prefer the longer IR when I've A-B 2K vs 1K points for a truncated version of the same IR. Again could be observer bias. Presumably the bass response is more important than the tail to my ears.
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Last edited by jonfields45; 11-21-2021 at 03:57 PM.
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  #4  
Old 11-22-2021, 12:05 AM
AeroUSA AeroUSA is offline
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When we I play my Matrix I think to myself. “If only the plastic artifacts were not there this would be perfect”. You are definitely on the right path.
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Old 11-22-2021, 12:18 AM
Peter Z Peter Z is offline
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Fantastic idea, Cuki! The distant sound was the reason, why I went away from IRs and bought Anthems.

3>2>1

This might be what we need. I think, the Anthem does the same trick via adding a UST to the mic. A nice AND direct sound.
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  #6  
Old 11-22-2021, 01:00 AM
Cuki79 Cuki79 is offline
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Quote:
Originally Posted by Peter Z View Post
I think, the Anthem does the same trick via adding a UST to the mic. A nice AND direct sound.
Hi Peter, Anthem is a different beast because the crossover separates completely the content at 250Hz.

The UST provides the low end and the mic provides the high end. With the Anthem, the mic can basically handle most of the signal. (Remember human ear is most sensitive at 1-2kHz)

In my case the IR convolution is just there to spread a tiny bit of content above 900Hz over 1.3ms. The core sound in my case is shaped by standard EQ.

However the goal is indeed the same: Improve the tone while keeping a direct sound
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Last edited by Cuki79; 11-22-2021 at 01:06 AM.
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Old 11-22-2021, 10:51 AM
JackB1 JackB1 is offline
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Quote:
Originally Posted by Peter Z View Post
Fantastic idea, Cuki! The distant sound was the reason, why I went away from IRs and bought Anthems.

3>2>1

This might be what we need. I think, the Anthem does the same trick via adding a UST to the mic. A nice AND direct sound.
Same here. Every IR I tried live, including the new Voiceprint, made my sound and attack more distant and air-y sounding and I while that may be good for recording, I don't like it for live play at gigs. The Fishman Aura pedal was good for live use because you can control how much image you blend in and if set properly you retain most of the immediacy of the sound/attack and lose some quack. I still can't believe at this point in time there haven't been better alternatives from Fishman, Baggs or anyone else. It's debatable that anything produced in the last century can beat any of the older solutions (Anthem, Aura, Cole Clark/Maton systems). I wish they would just somehow improve the piezo pickup and come up with a cost efficient standard for most electro/acoustic guitars so we could say a permanent goodbye and good ridance to the Sonitones out there!
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Old 11-22-2021, 12:24 PM
jonfields45 jonfields45 is offline
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Quote:
Originally Posted by JackB1 View Post
Same here. Every IR I tried live, including the new Voiceprint, made my sound and attack more distant and air-y sounding and I while that may be good for recording, I don't like it for live play at gigs. The Fishman Aura pedal was good for live use because you can control how much image you blend in and if set properly you retain most of the immediacy of the sound/attack and lose some quack. I still can't believe at this point in time there haven't been better alternatives from Fishman, Baggs or anyone else. It's debatable that anything produced in the last century can beat any of the older solutions (Anthem, Aura, Cole Clark/Maton systems). I wish they would just somehow improve the piezo pickup and come up with a cost efficient standard for most electro/acoustic guitars so we could say a permanent goodbye and good ridance to the Sonitones out there!
The ToneDexter Character knob, besides ultimately blending direct pickup into the output, also transitions from a phase accurate to a minimum phase IR. The minimum phase IR front loads the energy (effectively shortening the overall delay of the filter) while still retaining frequency response accuracy. Sounds like you've tried them all, but maybe should give that option another live eval.

In my own usage, I've not felt like I've ever noticed this "air-y" issue (my IRs, Cuki's, ToneDexter, Aura). I even tossed the minimum phase option out of my IR generator. Maybe I've got the wrong ears to judge.
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Last edited by jonfields45; 11-22-2021 at 05:53 PM.
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Old 11-22-2021, 12:45 PM
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Doug Young Doug Young is offline
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Quote:
Originally Posted by jonfields45 View Post

In my own usage, I've not felt like I've ever noticed this "air-y" issue (my IRs, Cuki's, ToneDexter, Aura). I even tosses the minimum phase option out of my IR generator. Maybe I've got the wrong ears to judge.
I've heard this "distance" thing with some IRs, but rarely with ToneDexter or Voiceprint. Usually, when it occurs, retraining with different mic placement fixes it, tho some pickups just seem to get it more than others. The character/blend control usually also fixes it.

But I use ToneDexter for live use with no problem. It probably helps that I blend in an internal mic, which bypasses the IRs, and maybe adds back any small sense of immediacy that is lost.
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Old 11-22-2021, 12:48 PM
Cuki79 Cuki79 is offline
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Quote:
Originally Posted by jonfields45 View Post
The ToneDexter Character knob, besides ultimately blending direct pickup into the output, also transitions from a phase accurate to a minimum phase IR. The minimum phase IR front loads the energy (effectively shortening the overall delay of the filter) while still retaining frequency response accuracy. Sounds like you've tried them all, but maybe should give that option another live eval.

In my own usage, I've not felt like I've ever noticed this "air-y" issue (my IRs, Cuki's, ToneDexter, Aura). I even tosses the minimum phase option out of my IR generator. Maybe I've got the wrong ears to judge.
Jon is right, the character pot in TD is one solution, however I already investigate this path and wanted something new and less computing power hungry.

As far as Jon’s recipe, it has a “built-in” blend “by nature”. It thus sounds more direct and pickup-like than my own process. Again, Jon’s IR are long IRs and are as computing power hungry than TD.
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Old 11-22-2021, 03:11 PM
JackB1 JackB1 is offline
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Quote:
Originally Posted by jonfields45 View Post
The ToneDexter Character knob, besides ultimately blending direct pickup into the output, also transitions from a phase accurate to a minimum phase IR. The minimum phase IR front loads the energy (effectively shortening the overall delay of the filter) while still retaining frequency response accuracy. Sounds like you've tried them all, but maybe should give that option another live eval.

In my own usage, I've not felt like I've ever noticed this "air-y" issue (my IRs, Cuki's, ToneDexter, Aura). I even tosses the minimum phase option out of my IR generator. Maybe I've got the wrong ears to judge.
Never tried the TD but probably won't due to it's cost. I'm pretty happy with my current sound which is a Anthem SL into a Acoustic Flyrig.
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Old 11-23-2021, 04:58 AM
Peter Z Peter Z is offline
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I had the TD for a while and couldn’t create an IR and setting the satisfied me in a live environment. And I tried my best with Neumanns mics and Neve, API and Millennia preamps.

I think it worked much better with fingerpicking than strumming or flatpicking. While I pingerpick 75% at home I only do that 15% live. That might be a point to consider.

I LOVE the idea and the efforts of the TD people, but while it’s almost there, it sadly didn’t work out right here. Went back to the Aura spectrum and soon later to Anthems or Anthem SLs. So far those are the best pickups I ever had in more than 40 years.

Something simple as the passive Schatten HFN (no superglue, nothing under the saddle, simple install) with a good working IR preamp would be a dream thou.
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Old 11-23-2021, 04:50 PM
JackB1 JackB1 is offline
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Quote:
Originally Posted by Peter Z View Post
I had the TD for a while and couldn’t create an IR and setting the satisfied me in a live environment. And I tried my best with Neumanns mics and Neve, API and Millennia preamps.

I LOVE the idea and the efforts of the TD people, but while it’s almost there, it sadly didn’t work out right here. Went back to the Aura spectrum and soon later to Anthems or Anthem SLs. So far those are the best pickups I ever had in more than 40 years.
Anthem (or Anthem SL) + Aura Spectrum is a great combo and tough to beat for live play.
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Old 11-24-2021, 05:17 PM
shufflebeat shufflebeat is offline
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Quote:
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...I tried my best with Neumanns mics and Neve, API and Millennia preamps.
Obviously our expectations and requirements are likely to be very different but all my "better" mics made less satisfying W/Ms, the most effective has been a humble sm57 at the neck join with the soundhole plugged during training.

My last mic purchase was a Slate ML2 which, on paper, is ideal for the job but still comes second to the '57.
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Old 11-24-2021, 07:36 PM
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Quote:
Originally Posted by shufflebeat View Post
Obviously our expectations and requirements are likely to be very different but all my "better" mics made less satisfying W/Ms, the most effective has been a humble sm57 at the neck join with the soundhole plugged during training.

My last mic purchase was a Slate ML2 which, on paper, is ideal for the job but still comes second to the '57.

Yep, my "best" mics did not do a better job than others, and not what I've ended up using.
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