GUITAR CABINET IR'S - How long should they be to SOUND GREAT? 

you can also play the same signal through both IRs simultaneously with the phase flipped on one. If you hear silence, they are 100% the same

When emulating a larger cabinet like a 4x12, the longer IR helps capture the resonance within the cab, lasting longer than the original transient. To me the IR length under 50 sounds more like a close mic'd 1x12 or 2x12, the most noticeable effect of this of course being the changes in the low end, but without a doubt one of the biggest factors of a half stack's massive sound is that cab resonance.

Thank you so much for this video Pete! I'm doing my IRs this week and this video was really useful!

Great video Pete! Really interesting how much the IR can make a difference. Always learning when watching your videos. Thank you.

Thank you so much for this demo Pete! I had questions about this, and you've answered them. Much appreciated.

Thank you so very much Pete. I’m new to the use of IRs and I’ve been seeking out useful, practical information as well as sound theory to guide my understanding and use based on my comprehension. Most of the commercial IR creators seem to offer a mixture of marketing and voodoo. Not you Pete. Your pragmatic instruction and information is just what I seek. Again thank you sir.

Thanks Pete for an awesome video explaining the IR length issues. I started using IR's on my Helix very soon after I got it. One of the first things I learnt about them is they need a -18db value to make them sound real. I got that value buy luck zooming in on a value on a video. Never looked back after that and always use IR's. Again thanks for all you do for us guitarist. Cheers Mike

That's a ton of good useful information you've been sharing on RU-vid! This is the last thing I wanted to know but bought some Celestion IR's that come in 200 and 500ms so I had to see if I could find out what the hell the difference is and sure enough you had it. Thanks!

Finally a good video about this subject. Like you said we should use our ears... Good job Pete.

Thanks for this Pete, really found it interesting and learnt something useful too!

Killer tone Pete! I too can hear the difference personally like the 200ms it sounds more natural. I’ll have to buy those IRs they sound phenomenal. Thx for the video and BTW love Sunday simulcast. ✌🏻

Great video Pete! Very useful, informed comparison. Those super short IRs were reminiscent of the tones in my Digitech RP155 from when I first started playing guitar, lol.

Great tone experiment Pete! I noticed a difference at 7:32 on into the video...but yeah...couldn't really hear a differenc earlier on...in a car stereo system. Thanks for all you do!

Thanks so much for this, the times on the Celestron IRs confused the heck out of me!

black shuck is such an epic riff. I love it to. Great vid Pete thanks

That was a very cool comparison!! Thanks for another awesome video, kind sir.

Hi Pete. I know this post is a few years old but I wanted to thank you. Nothing sounded good enough for me on my Helix, virtual amps, etc. So I decided to download this Suhr 4x12 Greenback IR. I thought if Pete likes it it must be good , right? I'm so happy I did. I don't have money to buy a lot of IR's, but this one sounds great everywhere, cleans, low and high gain rock, metal, ACDC, Hendrix, Van Halen, Maiden, you name it. You gave new life to my Helix. So THANK YOU very much Pete.

I see new vid from PT - i hit the thumb. Nothing but evidence in simplicity. Great as always

The 200ms IR was more reverby, but I wouldn't have noticed in a mix. The difference between 50ms and 18.5ms was almost like the difference between pretty-good fret-hand muting and excellent fret-hand muting, but more as if you were muting reverb as opposed to actual strings, if that makes sense? 12ms was where it went from being acceptable to too short for me, but around 18-25ms seemed to be my favorite length... and over 50ms was almost to echoey. I would not have expected that specific of a preference, and for sure before this video I would have just assumed that the full, non-truncated length would have been my preference. Thanks for the awesome comparison. That PT15 sounds great!

Thanks Pete, great video. This answers the Helix question that 1024 is ok for IR sample rate.

Maestro PT - You make some of the most useful videos in the history of film. Thanks, big dawg.

Very informative! Thanks Pete!

This was so insightful! I know Strymon Iridium goes all the way up to 500ms in stereo. My Ownhammers are at 200ms. I thought that was just them going cheap. Turns out that’s so overkill. I could hear a little more in your midrange at about 50ms at the end, but in all, this was a solid comparison. Thanks Pete!

Really informative video as per usual thanks Pete. Will you be reviewing the Boss Waza Tube Amp Expander?

Awesome! Thanks Pete! I think the loss of bass probably at shorter milliseconds is possibly related to lower frequencies having longer waves (and so it takes a little longer to capture them) but I'm no physicist! I do love my Two Notes Torpedo Cab, bought in no small part thanks to your demo!

Great video Pete! You have very effectively addressed a debate which has raged through some guitar forums I frequent. However, I would like to add a note just for the sake of clarification. I know you mentioned this in passing at the beginning. But in the case of some IR's, the length is crucial to the overall sound. I am thinking specifically of room and ambient space IR's which are used in some convolution reverb plug-ins. I know that I have a collection of IR's in one of my Waves plug-ins which includes snapshots of some of the most famous studio drum rooms (as well as other acoustic spaces) in the world. And truncating those IR's would definitely have a detrimental effect on the sound, as the overall ambience is actually a very important part of the IR in itself. While 18-20 ms is probably more than enough to do justice to a close mic'ed guitar cab, it simply cannot capture the essence of, say, the Abbey Road main recording room or the Vienna Opera House. And in the case of at least SOME guitar cab IR's on the market these days, a well mic'ed room is actually part of the overall sound. Somewhat obvious, I realize. But an important distinction nonetheless.

As always Pete, a wealth of knowledge!!

Great vid!!!! This whole time, when I use Helix native I've been using 2048, but really there's no point.. thanks Pete. Great experiment

Thanks Pete - I was just googling this question when trying to decide between the Mooer RADAR or the Two Notes CAB-M. Incidentally, your old article on Premiere Guitar was an early hit on the Google, and here you are 7 years later with more good info.

Thanks! This is really helpful!

Woah, thanks for helping me understand how the IR length affects the overall picture

Pete thorn show is like sitting with a next door neighbor in a conversation! cheers Pete thorn.

Great video Sir

Big thanks for this video!

Good morning Pete! You are a great guitar player. Cheers! ☕

Great demo!

Awesome and interesting as usual, Pete. I had not seen the MixIR before by Redwirez so that was especially intriguing. Although I use Studio One and not Logic, I would be very interested in seeing how you set up your "signal chain" to run guitar straight into, say one of your Apollos, into Logic with whatever amp sim you are using as a plug-in, into MixIR. I don't think you said whether or not you are using the Big Box or only the MixIR. Anyway, just a somewhat quick demo of how you set up to do a pedal or other demo video, or even just to practice, using the MixIR. Kinda sounds like it would be an advert for them, ha ha ha! On another note, I had not heard of Transcribe! until you showed it recently in a video on how to learn songs quickly, and I demo'd that and am using it daily now. Great piece of software and very helpful! I hope they gave you a cut of sales after that video too! :+)

great video, i will test this with some 500ms IRs from OH.

Excellent demo Pete, very helpful. I can hear a difference, the 20.5 mS seems tighter and more focused. Due to slightly less low frequency response or addition of room reflections, who knows? These will be great for live use, and in a recording situation if a longer IR is needed, easy to use the DAW. Sound logic ; )

this is super interesting stuff for me. I just recently started to use some pretty good free IR's however I made the experience that some of them seemed a little to bass heavy for me. So judging from this video I might try to shorten some of the IR's to maybe get the low ends in check and try if it works for me.

Okay after listening about 20 times i think that I hear despite my bad ears (or maybe because of) I could hear a clear difference already in the first example between the PT and your computer (mix ir2 200 ms). It was definitely more dry in my ears. The question is how much it does matter in the mix, probably not at all with reverb and delay on. I can totally agree that 20-25 ms should be enough. As always a great video!

Thank you

Really interesting topic, I'm super fussy about my IR sounds so i found this really helpful. Thanks as always for your time.

I agree with you. That first Darkness album is fantastic. Below 11ms sounded like the point of loss.

From an IR producer's perspective I spend a lot of time getting clean captures all the way up to 500ms. I do agree with Pete that most of "the tone" will be the first 20.5ms but a big part of the low end resonance happens after that - this is why Cliff from Fractal Audio introduced the UltraRes format that goes up to 170ms. It's very clear if you use a low end heavy mic like a Royer R-121. With 500ms you're also capturing the room resonances and this will be much more realistic sounding if you capture it in the IR vs use a reverb effect afterwards. We're talking IR reverb vs algo. That being said it's a subtle difference that's inaudible in the mix.

Excellent info. Well done. Phil NYC Area

Thank you so much for this Video!

oh man! This is so helpful!

8:10 there is a noticable change in "room" sound, when the IR goes from 26 to 40ms. I think the room info might be an important part of the "realistic" feel of a Mic/room. But ofc it can also be disturbing...if you want a short and dry sound. Nice if you can just dial the length of the IR's. :)

Thanks Pete! Damn good info here.

That 18-20ms area is clearly a golden point, as it contains the best qualities of the wave, and not having "messy" reflections, that would be unwanted, especially in a mix.

A little late on watching this but right around twelve I noticed the bass drop!

Great demo Pete! I too use MixIR2 w/Celestion IRs and had no idea that lowering down that far from the 1800 ms max would still give a great sounding result. Any idea if this goes even further in reducing the already low latency? Thanks!

I noticed a noticable difference between the 200ms, vs 20.5. This was listened to with 10 driver in ears.

Sounds a bit thinner through the daw on first test. IR's from the amp are a bit fuller, a bit more lows and mids = more aggressive tone :) You rock Pete!

Can't tell the difference from 18ms-20.5ms. Could be the RU-vid compression. The new Axe FX III firmware update has added IR length controls so I'm gonna test it myself! Thanks Pete!!!

Excellent video as always. So if low end regularly gets filtered out on guitar recordings a 512 sample points IR (roughly 10 ms) would be sufficient ? Maybe not for bass guitar ? or I am oversimplifying ?

Excellent vid. I've been waiting for someone to test this in the real world for a while because, in your head you can't help but think "suhrely longer is better" (you see what I did there :O) but this proves that actually you only need about 20ms to get great results. It also reminded me that when I think of the price of the PT15, I always forget that you have the IRs AND a Reactive Load at that price. Keep up the great work, eh?

Very helpful video! Definitely clears up the forum BS thats all over the internet.

Pete rocking the scientific method! Great content as always.

Is this how I spent my life now? This is so stupid. I love it! Thx Pete

I completely agree with Pete- trust your ears and nothing else !

There WAS a volume difference between the two on the amp test but the tone itself was so close as to be negligable. On the shortening test, you got it right, 20ms is about right.

One thing I notice is that the Les Paul Custom always sounds fantastic for the rock riff parts you do lately. Bark and bite.

That riff is so badass.

When will you do the follow up to your studio tour showing us your cabinet room with iso boxes or whatever you do when you mic your cabs!

I'm assuming the loss of low end comes from the length of the low sine waves being cut off by the IR's decay at lower lengths?

I found the pt ir in the first example to sound right, where the full length from pc sounded stuffy like an old pod bean

Spot on man.

that black les paul custom is your most rock guitar!

To my ears 20 ms lost some top end and airyness compared to 200. Below 20 ms, you can hear the low end bleed off as well. Maybe the top end bleed off is desirable in some circumstances, and the low end roll off as well. After all, we often change mic positions to get similar end results. Anyways, this was very helpful, thanks for posting.

The IR hosted in the Suhr at 20.5 ms sounded noticeably clearer compared to IR hosted in computer at 200 ms.

Black Shuck is my sound check riff every time.

For me the 20.5ms sounded more in your face and like playing on a real cab. More responsive, but i don't know if i'm hearing it right with my headphones.

Losing some low end might not always be a bad thing... It all depends on the mix!

I doubt it really needs to be longer than 25 or 30ms. Low frequencies on guitar tracks will be cut out in mixing anyway.

Very cool and useful, thx! The difference between 20.5ms and 200ms was almost impossible to hear. In a studio-mix or even a live-setting it´s not noticable anyway. From 18.5 down to 10 it was still ok and usable, everything below 6ms was unbearable :D Or on the other hand useful for some psychedelic-post-punk-noise-rock guy :D

Excellent video. More science, less flaky “it’s the vibe of the thing” opinions. Nice.

Please demo a line 6 amplifi TT with an IR

It’s basically the same as sample rate. Higher sample rates can capture higher frequencies, and beyond a given point those frequencies are inaudible. The length of the IR sets how complex the frequency response can be. This doesn’t mean that a shorter IR can’t reproduce lower frequencies, just that it can’t shape them in a meaningful way. Physical speaker cabs do have fairly complex frequency responses, but just like with sample rate, there’s a point beyond which it doesn’t matter. I mostly agree that 18ish ms should be plenty, but it doesn’t hurt to have more!

I'm thinking of getting a "st.Rock React:IR" and the specs say Max:190msec. If I load a 200msec or 500msec file into it, will it work, or do I actually have to shrink the file below 190msec ????

Hey Pete - question about the PT15; have you & John planned for how owners of the PT15 update the onboard software needed for the IR technology?

Many of the Own Hammer (and other) IR packs have 200ms and 500ms options. Is there any reason/advantage to having 500ms?

History has shown, the longer the better. Not a debate any more.

Do you recommend a specific app to reduce the length of an IR? I just got a Sonicake ir loader and the Max length it accepts is 100ms. Just wondering if I buy a pack of IRs that are 200ms will they get auto truncated and will they sound bad. Thanks in advance for any help.

Brian Wampler just made a video on impulse response length, the title is "Impulse Response Cab Sims Explained Better", it looks a bit like an answer to this video. He claims longer IRs sound better.

I seemed to hear a little something happen when you got above 50ms but in what mix would it make any difference. I guess chances are that in the mix you will be doing some level of EQ'ing and effecting thus negating any difference straight away. I could almost see someone going down below 2ms and an effect (of course there's probably a better way to get there). Great video Pete!

I heard a change @ 12

What about room mics? Like a condenser 1-2 meters from the cab? Then it might start to make sense having longer IRs, right?

Like! having said that, let's watch the video...

If you were to create an IR for a distance mic how long should it be? I'm interested in using a Beatles style bass cab mic setup live. They would record a bass cab from like 8 feet back for a roomy sound. It can sound amazing, and to have that live would be a dream.

Hi Pete. Hope everything is going great with you. Thanks for doing this video. I just recently started researching IRs. I read that some IR Loaders are somehow better than others. I grabbed the free Loader from Nadir and the free IRs from REDWIREZ. I guess they're not terrible , but definitely don't think they sound as good as what you've just posted. If and when you have time could you share your opinion about this ? Thanks and have a great day. 🎸🎸🎸

I can hear the difference between the 200 and 20 but whether that is a good thing or not whatever haha. The really long irs give a little room flavor which can be cool too.

listening on a 5.1 surround and I thought the 20.5 second IR sounded punchier and added clarity...

Couldn’t you show the signal through some type of EQ to show the frequency loss across the spectrum as the IR length shortened

Black Shuck! All i know is your amp sounds awesome!

Hi pete...✌💞

I purchased some celestion IR's recently. I know I'm getting old, but I only expected a few files. Ended up with so many mic variations at so many sample rates and proximities. They all sound great to me. How do I even begin to choose what's best? So complicated.

Your friend is right! You don't need longer than 21ms and you can prove that with just simple math... 1024 samples at 48khz mono channel is 21.33ms... which includes bass below 50hz which you will cut out anyway in the mix on the guitars... why would anyone need or want a longer IR... all it does is consume computational resource.

I immediately felt the shorter was brighter