What is an impulse response?

An impulse response (IR) is a measurement of how a system or device responds to a sudden, short-duration input signal, known as an impulse. In the context of audio engineering, an IR is often used to capture the response of a physical space, such as a room or a guitar cabinet, to an impulse signal. The impulse response can then be used to simulate the sound of that space in a digital audio system, such as a reverb plugin. IRs can also be used to model the response of other types of audio equipment, such as microphones, speakers, and guitar amplifiers.

The best way to capture an impulse response of a guitar cabinet is to use a high quality microphone and a device called an impulse response (IR) loader. Place the microphone in front of the speaker and play a recorded impulse signal through the cabinet. The impulse response is then recorded by the microphone and can be loaded into an IR loader to be used in digital modeling software. It is important to use a high quality microphone, such as a condenser microphone, to ensure accurate capture of the impulse response. Additionally, it is best to capture the impulse response in a treated or anechoic room to minimize any reflections or ambient noise. 

What is the step by step process in capturing an IR?

1. Prepare the impulse signal: An impulse signal is a short, sharp sound that is used to excite the system or device you want to measure. A common impulse signal is a sine wave sweep that spans the entire audio frequency range.
2. Position the microphone: Place a high-quality microphone in front of the guitar cabinet, making sure that it is pointed directly at the speaker.
3. Play the impulse signal: Play the impulse signal through the guitar cabinet, while the microphone is recording.
4. Record the impulse response: The microphone will capture the impulse response, which is the way the guitar cabinet responds to the impulse signal.
5. Import the impulse response into an IR loader: Use software such as an impulse response loader to import the impulse response.
6. Adjust and process the IR: You may need to adjust or process the IR to remove any unwanted noise or to change its characteristics.
7. Save and use the IR: Once you are happy with the IR, save it in a format that can be used in digital audio software, such as a convolution reverb plugin. The IR can then be applied to audio recordings to simulate the sound of the guitar cabinet in a digital audio system.

To create an impulse response, a short burst of sound (the impulse) is played in a physical space, and the resulting reverberation is recorded. The recording is then analyzed to generate a mathematical model of the space’s acoustic properties. This mathematical model is the impulse response.

Impulse responses are typically created using a technique called convolution, which involves applying the impulse response to an audio signal to simulate the effect of the physical space or system. For example, convolution reverb applies an impulse response of a particular space, such as a concert hall or a church, to an audio signal to make it sound like it was recorded in that space.

Impulse responses are also used in other areas of audio engineering, such as acoustic modeling, which involves creating virtual acoustic spaces for sound design and production.