IR loader pedals

[pilau]

Anyone here using an IR loader pedal? (Mooer Radar, Torpedo C.A.B. M, Nux SS-5, Hotone, Joyo, etc.)

Do you hear aliasing artifacts? That's the harmonic reflections that you can hear when playing through digital amps/sims (even hardware ones like Boss Katana or UA OX), for example, try playing double stop bends - your will hear a 3rd note sweeping down as you are bending up.

What is your experience? Thanks

[BlitBit]

I do not have an IR loader pedal but according to my theoretical knowledge they should not be susceptible to aliasing. The only place where aliasing could potentially occur is when the analog signal is converted into a digital one and vice versa. But this is a "problem" that all digital effects have and it should not really be a problem if the pedal has a good analog-to-digital converter. I assume that this should be the case for all modern pedals.

Applying the impulse response to the signal in the digital domain cannot introduce aliasing artifacts because it's an operation in a linear time-invariant system. These operations only act as filters on the signal. In the end what happens when you apply an impulse response to the signal coming from an amp or amp simulation is that you filter out certain frequencies. You can imagine an IR response as the application of a very complex static EQ curve to the signal. There are at least three elements that play a role in how that EQ curve looks: the speaker (although this might have non-linear elements in the case of speaker distortion), the cabinet and the microphone that was used to create the impulse response.

Aliasing mostly occurs when you apply a non-linear process to the signal, e.g. if you distort the signal. So aliasing is for example relevant if you use an amp simulation because it has to potentially simulate several distortion stages in the preamp and poweramp.

The tone that goes down when you do a double bend is not an effect of aliasing. In fact it also occurs if you play a double bend through an actual amp and speaker cabinet. It's caused by the time-varying modulation between the two notes that become more and more similar during the bend.

[CapnLockheed]

Not yet. But thanks for posting the question. I'm extremely interested in such a critter.
I have also noticed that there are also some amps being released with built in IR loaders.
A flat amp with a cab loader would, I think, make a nice complement to hardware modelers. Line 6's powercab plus amps have both onboard modeling and the ability to load your own IRS.

https://line6.com/powercab/

[imrae]

Some cab sim pedals (e.g. Radar, CAB M) include a power amp distortion stage which could alias. I wouldn't expect it to be that much of a problem compared to a high-gain preamp simulation, though.

The actual IR part won't alias, as BlitBit explained.

[pilau]

Thanks for the wonderful and detailed response. You covered all grounds basically!

The tone that goes down when you do a double bend is not an effect of aliasing. In fact it also occurs if you play a double bend through an actual amp and speaker cabinet. It's caused by the time-varying modulation between the two notes that become more and more similar during the bend.

Color me confused by I have never noticed that sweeping tone before on an analog amp. Do you maybe have a recording on hand showcasing that?

I am sure you know what you're talking about, but just to make sure we're on the same page, I am referring to aliasing as demonstrated here: https://www.youtube.com/watch?v=Ic4bVbXfdW4

[BlitBit]

Thanks for the wonderful and detailed response. You covered all grounds basically!

You're welcome!

The tone that goes down when you do a double bend is not an effect of aliasing. In fact it also occurs if you play a double bend through an actual amp and speaker cabinet. It's caused by the time-varying modulation between the two notes that become more and more similar during the bend.

Color me confused by I have never noticed that sweeping tone before on an analog amp. Do you maybe have a recording on hand showcasing that?

I have just recorded a short demo for that effect. I used my Hughes & Kettner Tube 50 that was recorded with a Shure SM57:
https://soundcloud.com/blitbit/double-s ... -goes-down
If you want to reproduce this effect I have used the following double stop here: 12th fret on the high E string and 15 fret on the B string with the B string bent one whole step.

I am sure you know what you're talking about, but just to make sure we're on the same page, I am referring to aliasing as demonstrated here: https://www.youtube.com/watch?v=Ic4bVbXfdW4

Yes, that's the type of aliasing that I was writing about. The video gives an example for the non-linear effects that are introduced by limiting. Compression and limiting are also a form a distortion and distortion introduces harmonics above the fundamental frequency. This is also what happens in a real amp by the way. The frequencies that are added by the distortion above the fundamental frequencies (harmonics) add "color" to the sound and are what makes the sound more interesting and more pleasant to listen to.

In a real amp there is no restriction where these harmonics can "go" because there is no sampling or sample rate involved. In a digital process with sampled data there is a sample rate and the Nyquist frequency (half the sample rate). All harmonics that would in reality go in places higher than the Nyquist frequency can't do so in the digital process and are folded back in the other direction towards the lower frequencies. If they reach the "left" end of the spectrum they are again folded back to the right and so on.

[pilau]

That's amazing of you to go to such lengths. Thank you.

I do understand the theory of it all, and listening to your recording I am quite shocked because I've always assumed this phenomenon exists only in amp sims.

Maybe you can tell me, however, why is the effect so profound in your recording, but not (for examples) in the videos below?

Multiple examples at the beginning:
https://www.youtube.com/watch?v=1MSnYiXMZ0g
And multiple examples at 1:23
https://youtu.be/JOJHXwN5O_E?t=83

[BlitBit]

[...]
Maybe you can tell me, however, why is the effect so profound in your recording, but not (for examples) in the videos below?

Multiple examples at the beginning:
https://www.youtube.com/watch?v=1MSnYiXMZ0g
And multiple examples at 1:23
https://youtu.be/JOJHXwN5O_E?t=83

I think there might be two factors at play here why it's profound in my recording but not in the two videos:

• The speed of the bend. If you perform the bend very fast like in the second video you won't be able to hear it very well because the two notes will become too even too fast. At the end of the bend their frequencies are very close to each other. This in turn means that the modulation frequency becomes very low and it will go below the hearing threshold of humans. If you listen to my bends they are done rather slow so that you can hear the tone in between the starting notes and end notes. But in the end of the bends it's also gone.
• The level of distortion also seems to play a role. For example if I do a bend with a clean amp I don't really hear much of the effect. However, as the distortion is increased it becomes more noticeable. My theory is that the third additional tone is quieter compared to the other two tones. However, as mentioned above compression is distortion and distortion is compression. I think that very high distortion compresses the signal so much that the third quieter tone becomes much more noticeable because it gets increased in volume a lot whereas the two louder tones cannot increase in volume as much as the quieter tone as they are already quite loud.

[imrae]

https://en.m.wikipedia.org/wiki/Intermodulation

It's the reason power chords sound amazing at high gain but complex chords sound noisy.