Roll Your Own Reverbs!
Simulate Spaces with Impulse Responses

Location, location, location: IR reverbs can make your guitar sound like it was recorded ANYWHERE!

Impulse response reverbs are one of the handiest tools in the digital-audio junk drawer. If you’re new to the concept, prepare to be amazed. (And if you’re familiar with the technology, jump to the end of this post to score some cool free reverb sounds.)

Impulse response reverbs, also known as IR or convolution reverbs, fake the sounds of genuine acoustic spaces. Say you want to be make your tracks sound as if they were recorded in a 12th-century dungeon: Just visit your nearest medieval castle and set up a small PA system in the dungeon. Next, play a test signal (usually a sine-wave sweep or a starter-pistol shot) and make a recording of it echoing in the space. Back at your studio, your IR software compares the new recording to the original test tone, and creates a reverb preset that you can apply to any audio source. Just slap it on a guitar track, say, and voilà — you’re rocking out in the dungeon, minus rats, mildew, and torture implements.

But wait, there’s more! You can use the same technology to mimic hardware effects and speakers. Just run the test signal through an amp or effect, and you’ll have a digital clone of the physical device. Here’s a brief video demonstrating the idea:

If you use amp modelers, there’s a good chance you already use impulse responses, since they are one method modelers use to mimic amps and speakers. But you need a dedicated impulse-response reverb plug-in to make and mutate your own IRs. In the video I used the one included with Apple’s Logic Pro, but there are number of free IR reverb plug-ins available for both Mac and PC.

Audio Ease's Altiverb includes an amazing IR library.

They all sound about the same — the key distinction between the freebies and the premium plug-ins is the quantity and quality of the included IR library. For example, Audio Ease’s Altiverb costs over 500 bucks, but includes an unrivaled collection of modeled spaces, including many of the world’s greatest concert stages and recording studios, plus fascinating stuff, like Wendy Carlos’s plate reverb and the Bill Putnam echo chamber used on a huge percentage of LA rock hits of the ’60s. (FYI, Audio Ease’s impulse responses are copy-protected, and can only be used in Altiverb.)

Another cool option for Mac users is Space Designer, which is included with Logic Pro, whose retail price has just been slashed to US$199. [DISCLOSURE: I’ve been a compensated contributor for both Altiverb and Logic Pro. Or to put it another way, if you buy either program, you get some cool IRs I’ve made. :smirk:]

(At this point, conniving minds may should be thinking: “Hmm — can I run a test signal through my friend’s Marshall plexi, and have an instant stack-in-the-box?” Sadly, no — IRs only capture static states, and can’t mimic anything as complex as an amp, whose tonal response varies dramatically according to the input signal. The responses of rooms, speakers, and effect hardware also change according to input, but much less obviously. Some listeners say they respond negatively to the static quality of IR reverbs, but I’m not one of them. Also, FYI, the latest version of Altiverb includes an LFO modulator that can add a lifelike touch of randomness.)

You can read more about impulse responses in this Wikipedia article about impulse responses, and this one about convolution reverb — all written by people who, unlike me, actually understand the math.

All I know is, IR reverbs are frickin’ cool. Have a few on me: Here are impulse responses for the three sounds heard in the demo video: the goopy Baldwin amp reverb, the claustrophobic styrofoam box, and the lush Real Tube stereo spring reverb. The zipped file includes both AIFF files for Mac geeks and WAVs for PC droids. Consult your plug-in documentation for installation instructions.

Free Tonefiend Impulse Responses (2.2MB download)

Kids, do try this at home. And be sure to share the results with your tonefiend.com classmates!

14 comments to Roll Your Own Reverbs!
Simulate Spaces with Impulse Responses

  • el reclusa

    Thanks Joe, and happy New Year!
    This is pretty exciting…I’m finally joining the modern world of recording into a computer via Reaper.  I need to get a suitable interface, but in the meantime, has anybody tried any of the freebie convo reverbs out there?  Looks like there are a few, and I’m way too broke to buy one at the moment, so if anyone has tried any of these and has found one to be more user friendly or better sounding than another, I’m all ears!
    There was an earlier thread where this came up, and I mentioned a modeling amp that does indeed do something like this, allowing you to digitally clone an amp in much the same fashion.  I couldn’t remember the name then, but apparently it’s called the Kemper Profiling Amp: http://www.sweetwater.com/store/detail/ProfilingAmp/
    (No affiliation with Sweetwater, they just happen to be whose catalog I saw it in)
    I haven’t checked this thing out at all yet, but it’s certainly an interesting idea!
     
     
     

  • joe

    Yeah, I saw the video of the Kemper from last year’s NAMM show. I’m going to the show this year, and I’ll try to check it out.

    A reader wrote and told me he had good results with SIR1: http://www.knufinke.de/sir/index.php

  • Mat

    Great article (and thanks for the IRs). I had no idea it was this easy!
    I’ve been using SIR1 for a couple of years and found the sound quality to be pretty decent… the interface is nice and simple too. Haven’t felt the need to upgrade yet!
    The only real issue is latency but most DAWs compensate for this (http://www.knufinke.de/sir/sir1.php#plc).
    Definitely worth a try!
     

  • el reclusa

    Thanks fellas!  I’m gonna try it out ASAP!

  • I have been playing with these since 2002 or so when I started using Sonic Foundry Acid and  Sound Forge (now owned by Sony but they didn’t manage to screw them up too badly). Acoustic Mirror and a bunch of impulse files were included with most releases of Sound Forge. I mostly used it on recordings to subtract small amounts of the file run thu the Acoustic Mirror from the original un-effected file by mixing in a phase inverted version of the Acoustic Mirrored file. When applied to loops I built with my Boomerang pedal, it gave them an eerie and sometimes uncomfortable edge, for me the key was using subtle amounts. I always viewed this as one of my “secret weapons” which obviously now wasn’t so secret as I thought. I also created some impulse files of my own by recording them in the basement equipment area of the university science building I worked in, which brought in all kinds of noises like air compressors, steam pipes, water pumps and sundry other building noises along with the reverb of the space. I also did some in an early token ring network hub area where the mic was picking up all kinds of digital noise from the network hardware. The best impulse file I had was recorded next to a RF data-link transmitting antenna linking network traffic between buildings that injected noise in the form of audio rectification by the cheap mic I was using the test tone was sent from an old PA horn. When that was applied to an audio  files it sounded like aliens were giving landing instructions to ufos. I lost that file in a hard drive crash but used it on one strange song that was also lost in the crash. Not really useful for anything but noise based multi-track improv recordings (but I am a strange musician at times). These strange impulse files always seemed to work best as a subtractive element for me at least, especially when you EQ-ed the resulting file to a reduced bandwidth (for example just bass or treble frequencies with the mid-range dialed out). I usually moved the tone source as far as possible from the mic for maximal weirdness. I also had a set of impulses I made from feeding the tone into a coil and recording it from  guitar pickups as well as blasting the tone from the speaker at a turntable with the stylus sitting on record in the runout groove area at the middle of the record and recording the output of the phono preamp. There was also a great impulse file created by a pair of users sending the signal from a old school phone in front of a speaker to a microphone in front of the receiving old school phone across country both in rural areas with primitive phone service giving some weird echo, noise and distortion. I am not sure where the impulse file went but it was pretty strange sounding when applied to a recording.
    There is IMHO no limit to these kinds of things after all the sound of the light sabers in Star Wars was recorded from the inside of an old tube tv set. The sizzling of the 20,000 volts at high voltage transformer and connections was the basis of the sound effect.  They then manipulated that a bit and played the resulting sound thru speakers and re-recorded it by moving a microphone in the room like the light saber moved in the films. I take a lot of cues from sound effects creators for my stranger recordings especially from the Old Time Radio sound effect guys who did amazing things with common objects and they usually did it LIVE!!

    • joe

      Wow — I gotta admit, that sounds right up my alley. Don’t suppose you feel like SHARING any of the IR files, do you?

      Ever play with Audio Ease’s Speakerphone? It’s basically an IR reverb with lots of samples of funky speakers, walkie-talkies, and so forth.

      • I have actually been looking for them to see if I have copies anywhere. I had a hard drive crash and lost the working files but I may have backups somewhere. I am rather ashamed of losing stuff in that crash since I was the admin and computer hardware guy (and electronicist, superconducting magnet nursemaid, designer, builder and left field idea man but not a chemist) at the university chemistry dept. I worked at for 15 years. I diligently backed up everybody’s data and files but my own apparently.  Anyhow I will keep looking for the IR files but they were for Windows based software tho’ it sounds like you can convert them. It seems to me that “old school phone to old school phone” IR files should be floating around the web somewhere (tho’ I got my copies along with some experimental sound manipulation software from a strange guy named Al I met when he played with Eugene Chadbourne back in the early 2000s).  I have a ton of CD-Roms to look thru for the IR files so it may be a while but if when I find them I will get them to you (I need to catalog and reorganize the stuff anyway).  I am looking forward to trying the files you posted as well. But you have also inspired me to crank up the Acoustic Mirror software and make some more weird IR files (I’ve got some great ideas). I tend to push things to and beyond the breaking point and use software and hardware in unintended manners which sometimes unnerves some (but not all) of the people I play music with.
        As for Audio Ease’s Speakerphone I have never used it. I went to the site and watched the demo it is very impressive, and I really want it!!! Speakerphone would be such a wonderful toy useful tool. I am assuming as a plugin I could use it with Sonic Foundry Sony Vegas (I really don’t need another excuse to buy a Mac). Speakerphone looks to be a very well designed software tool and the supplied IR’s and samples look very complete. I can see this making a hole in my wallet. Guess I’ll be looking in to it soon. I love and hate you for telling me about it if you know what I mean :-) .  Thanks for the site and your hard work in putting it all together for everyone’s use.

      • I just ordered SpeakerPhone and an iLok so I can move it around from my studio to the Boredroom  where I also record, mix and master (my bedroom with a computer duplicate of the studio as I spend a lot of time in bed due to “failed back syndrome” it keeps me relatively sane). I am looking forward to playing with using this software on my next W.T. Fits project (it’s an anagram for “What the F..K Is This S..t?) as well as other projects. Thanks for the recommendation I had never heard of it. I highly recommend everyone go watch the demo at:
        http://www.audioease.com/Pages/Speakerphone/speakerphone_themovie.html
        It will blow your mind but it is 22 minutes long. Be warned it may make a hole in your wallet!!

  • daveyohill

    Hey Joe, Nice article. The link for the impulse responses in the article seems to be dead though. By chance are the IR’s mentioned already included in the Logic/MainStage library?

  • CONfused

    Hi. I’m confused. In one paragraph you say “…You can use the same technology to mimic hardware effects and speakers. Just run the test signal through an amp or effect, and you’ll have a digital clone of the physical device…”

    But then in another paragraph you say…”(At this point, conniving minds may should be thinking: “Hmm — can I run a test signal through my friend’s Marshall plexi, and have an instant stack-in-the-box?” Sadly, no — IRs only capture static states, and can’t mimic anything as complex as an amp, whose tonal response varies dramatically according to the input signal.”

    Confused, thanks for elaborating if possible!

    • joe

      That’s a great question, and you’re right — it IS super-confusing.

      An impulse response is a snapshot, based on the way a test signal (such as a sine wave) sounds in an acoustic space or through an electronic signal chain. If you run that signal through our hypothetical Marshall plexi, you capture the sound of the amp in a single, frozen state, with one unvarying signal running through it. But in analog reality, the sound changes when you adjust the tone knobs. Or change the gain. Or lower your guitar volume. Or play a little harder or softer. Or switch to an instrument with a different type of pickups. Change one detail, and the overall sound changes. Impulse responses can’t do that.

      So in practice, you might get an interesting effect from the single Marshall plexi snapshot, but probably not anything that feels or sounds anything like the experience of playing through a responsive and volatile analog circuit such as a plexi.

      But the effect is much more convincing when working with acoustic spaces or simulated reverbs.

      • Bebah Palulah

        Impulse responses are entirely analogous to the frequency response as long as the system in question is linear (no distortion creating new harmonics) and constant (no LFO modulation).

        You may have heard of the mathematical wonder known as the FFT (Fast Fourier Transform). If you take the FFT of the impulse response you get the frequency response.

        You can certainly get an impulse response of a distorted amp with whooshy chorus going on, but it’s not going to be easy to predict what the result would be using this in a convolution pedal. Which isn’t to say it wouldn’t be useful. :beer:

        When it comes to reverbs we don’t usually talk about the frequency response, rather the time behavior. Nevertheless, any reverb (or real acoustical space) will have a frequency response, which you could plot point by point using a signal generator. You’d just have to let the signal settle down for awhile after changing the frequency to get the steady-state level.

  • ed sison

    Hey Joe! Great article, thanks. BTW, the link for the Tonefiend Impulse Responses doesn’t work. Is there a new link? Thanks again. Ed

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