Impulse response and room tone

Question

Hi,

What is the main purpose of recording an impulse response?

Is it just to have an idea of the kind of reflections of the room you're recording on?

When to do it in a production?

Thanks.

Answer 1

an impulse response perfectly describes how an impulse behaves in a room.

if you know how an impulse behaves in a room you can accurately describe the behavioral of any sound in that space, using a technique called convolution.

http://www.audioease.com/Pages/Altiverb/sampling.php this is a really great video for explaining the basics.

the main purpose of recording an impulse response to is be able to simulate the acoustics of a space on another sound (either from somewhere you've been, or somewhere someone else has been).

impulse responses don't just have to be taken in rooms. any system (where you can record the difference between the input and output) can produce an impulse response, like a filter for example.

http://en.wikipedia.org/wiki/Impulse_response

http://en.wikipedia.org/wiki/Convolution_reverb

http://freeverb3.sourceforge.net/

http://www.audioease.com/Pages/Altiverb/index.php

http://www.waves.com/Content.aspx?id=250

as for when to do it during the course of a production, i can't really comment from a professional point of view. however, it is my understand that it is common practice to record impulse responses of any space where production sound is recorded.

Answer 2

Does anyone have any advice on recording impulse responses from their own experiences?

Answer 3

@Gaz

A tool like Apple's IR Utility included with Logic actually does most of the work for you. It assists you with the setup and where to place your mics, you feed it the information and measurements and provide it with a short sound like a whip crack or starter pistol or sine sweep and it deconvolves it all for you. Check out this link below for a little more info. It talks speciifically about space designer, but the method is really the same. IR Utility manual

Answer 4

I have the waves plugin IR-1 Convolution Reverb. They have a frequency sweep file on their website too that you can download along with instructions on how to do everything.

http://waves.com/content.aspx?id=96 > At the bottom of the page, you have to make an account to download it though.

Answer 5

I have done some IR's in the past couple of months. In my experience, it would be used mainly for production (matching ADR to production sound).

If you are on a production set and want to record some IR's, there are several ways to do it.

1. Using the sweep file (varying lengths) and recording the sweep tone in the environment (most accurate)
2. Recording the slate clap

Since production sets are kind of chaotic, setting up a speaker and recording the sweep may not always be a viable option. The easier solution would be to use the sound of the slate clap. However, this may not be as accurate as recording the sweep.