Impulse Responses (IRs) - Do you download, buy, or DIY?

Question

A little background: I'm trying to expand my library of IRs. While I have access to TL Space, Waves IR-L, and Altiverb the most readily available (installed in the room I do most of my work in) is TL Space. So I have another question in a multiple parts:

Question #1

I poked around the internet trying to find new and interesting IRs and found a few resources.

• Avid's TL Space IR Library
• The Audio Ease IR Library
• Waves' acoustics.net
• irlibrary.org

What other websites do you find useful IRs on?

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Question #2

After reading Tim's "Why Use High Sample Rates?" post (a great read, btw) I realized that people are (have been) selling library collections of IRs also. It makes total sense, just never thought to look.

Are there any collections that you highly recommend? Do you run into issues with compatibility ie a library was created for Altiverb and as such won't load into TL Space or vice versa?

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Question #3

As I understand it, pretty much any audio file can become an IR but not every audio file makes a good IR. If I'm choosing sounds from my effects library are there characteristics that I should I look for? Or is it better to not limit myself and just see what works?

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Question #4

When going out and recording your own, what do you use? At the present my theoretical rig is an iPod line-out > Genelec 1029a and an NT4 > MixPre > M10. I haven't quite figured out the battery power yet, but at first I plan on sampling spaces with wall power. I'm expect that I'll lose some low end using the 1029a, but is there anything else that I should expect / look out for? Also, is there a benefit to recording IRs at higher sample rates? Can the plug-ins even read the files?

Answer 1

I don't have time to address all your questions, but here are a few observations.

I love Altiverb, not just the software, but the company. The crew in the Netherlands has been the leader in IR technology for quite some time now. The IRs they offer every few weeks or so are also top notch and cover so many needs (although I can always, always use more outdoor stuff). Their impulse responses are always top notch.

I'm not a big fan of a lot of the free impulses you can find on the web (been burned with some stinkers that introduce a ton of noise into the signal) with the exception of two collections.

Fokke Van Saane's collection:

http://www.xs4all.nl/~fokkie/IR.htm

And these samples from the wonderful hardware verb the Bricasti M7, which were generously made free to the public by Casey the co-owner of Bricasti:

http://www.samplicity.com/bricasti-m7-impulse-responses/

I wouldn't limit yourself when using sounds as impulse responses, but my observation is that shorter sounds with envelope that has an initial transient and a tail work best.

Answer 2

1. Here's some libraries for Space Designer: (I'm a Space Designer loving guy)

http://www.macosxaudio.com/forums/viewtopic.php?t=14100

1. I've actually never tried pulling IRs from one program to another. Interesting idea though. I believe most use proprietary IR files, but it might be possible. If not, you could always use one IR to sample the other one, which would be a bit silly, but it'd probably work...

2. I've had the best luck with files with a heavy transient and then a nice long tail. Those are the most similar to the way a manually sampled IR would be done.

3. When I've gone out to do IRs, I bring my laptop, Mbox, mics (setup depends on what IR setup I'm going for), and I use JBL Eons as my speakers. I've had some good luck with the setup so far. The Eons are nice and powerful enough to "energize" big rooms.

Answer 3

Q1: I have only downloaded free IRs and swapped with other audio folks. Big fan of sharing!

Q2: I really have not used IRs so much to justify buying an entire library. The best use I've found is when I'm doing on-set recording to go ahead and get some IRs for the space I record in so the post audio folks will have something useful for that they can apply to dry effects, ADR, etc. I'm also curious to see responses to this question.

Q3: Best (purest?) IRs come from a sound that excites every frequency. I generally start with a 4 second burst that sweeps from 10Hz to somewhere around 24kHz. I've also heard a lot of folks like to pop a balloon, shoot a starter pistol, etc - key is to have an impulse that hits every frequency and has some time to decay in the space. Once you have that down, you can really do anything - hit a cymbol, scream, play back a lion's roar. It will all create something interesting and keep the essence of the impulse.

Q4: Sounds good, except I would use a single measurement mic (flat EQ, omni) or a pair of them. I have two Behringer ECM8000's that work great and they're generally about $50. You can spend more, if you like, but these do just fine. The other thing that is key - you MUST record at the same sample rate that you are outputting. I use files that are 48k and record at 16 bit. 24bit and above just bog down your processing. This is realted to deconvolving only, I'm not trying to get into a 96k vs 48k argument.

I HIGHLY recommend using Praxis's impulse files and deconvolver (web site here). The files automatically line up and it streamlines the process. Give the info pdf a read and let me know if you have questions on how it works. I've done a number of these now and it's very simple to create quality IRs. Also, it's free!

NOTE: I am fairly new to making IRs. I've been doing a lot on my own and learned a lot, but I'm by no means an expert.

Answer 4

re Q2 and Q3, it depends on what you want to achieve Are you wanting to add 'natural' acoustics to a sound ie reverb or delays Are you wanting to alter the sound in un-natural ways?

I've bought a bunch of IRs - the IR folder on my Mac is just over 10GB Its shared by Altiverb, TL Space & Waves - some work with all, others don't

The IR libraries I've bought & like are:

• Sanitarium (good twisted textures!) http://www.spiritcanyonaudio.com/

• Eventide H8000 http://www.kineticsoundprism.com

Can't remember where I got it but one IR I love is called MARs IR - someone made it for a space doco they were working on, basically a 90 second reverb on an expensive Lexicon = lovely soft textural verb... There are a lot of free IRs around the interwebs if you want to spend time searching... I have more than a few different collections from high end outboard devices...

re Q3 Its worth listening to raw impulses (I enjoy listening to delay ones as it reminds me raster noton music releases ;) But its especially interesting listening to more textural ones (eg the Sanitarium IRs) as it gives you ideas about sounds that could be useful to try when creating your own IRs... I dropped my whole IR folder into a seperate SoundMiner database - makes for fun listening!

I've said it before on this site so do a search, but the thing with convolution is that it reinforces common frequencies between the two sounds. So if you put a bass sound through a violin IR you wont get much. This also explains why when it comes to textural IRs the 'noisy' (ie full spectrum) ones are so useful...

I went through a phase a while ago making my own IRs - not with sines although I did a few with starter pistol - but using sounds. I have some useful ones of a group of people whispering (good to convolve with wind), tibetan monks, various animals, screams etc.. it is so easy to do there is no harm in just experimenting!

Answer 5

TLSpace imports the Waves Libraries

Answer 6

HISS from IRCAM is a good toolkit to do DIY Impulse Response. http://www.openairlib.net/ is a good resource for certain places and are free.

www.sound.codes is another good resource for the responses of certain Indian sounds.