Room Impulse Response

Room Impulse Responses (abbreviated as RIRs) are time-domain signals of frequency distribution, and amplitude decay as measured in a room during Room Acoustics Measurements. Impulse responses characterize a room between two given physical locations, assuming that the room is a stable, causal LTI (linear, time-invariant) system.

Room impulse responses have the following components:

• Propagation delay

the length in time the sound travels from the source to the listener

• Direct sound

in the line of sight, the direct sound is a peak corresponding to the shortest travel path

• Early reflections part
  • First reflection (usually the reflection from the ground)
  • Second and other reflections

more reflections still clearly distinguishable

• Reverberation Tail part

this is the stochastic part of the reverberation where so many reflections are present that they cannot be separated any more.

The Initial Time Delay Gap (ITDG) is the time between the direct sound and the first reflection, but sometimes it is defined as the time delay between the direct sound and the first reflection that is not a ground reflection, in the room impulse response. Pre-delay is usually meant as the ITDG.

Other representations of the room impulse response

Room impulse responses are always causal, therefore the following representations are equivalent:

• Time domain
  • impulse response (IR, RIR)
  • step response, obtained by integration of the impulse response
• Frequency-domain
  • frequency respone function (FRF), obtained by Fourier-transforming the IR
    • Absolute value of the frequency response: magnitude response
    • Angle of the frequency response: phase response
• Complex frequency domain
  • transfer function (TF), obtained by Laplace-transforming the IR