System Measurement

Introduction

This user guide section is entirely dedicated to the “System Tuning” layouts of the MiRA::Live version.

These layouts consists of a multi-channel “FFT” analyzer. It aims to analyze an audio system, more specifically a linear and time-invariant 1 one. One channel serves as a reference, while the others are compared to it.

In live system tuning, we usually excite the sound system with a known signal, such as pink noise or a logarithmic sweep. The reference is the signal itself, while the other channels receive the input from different microphones placed in the venue we want to measure. The multi-channel FFT then provides us with the transfer functions and the impulse responses of each channel.

The transfer function provides two key pieces of information:

  • The magnitude curve, which describes how the system amplifies or attenuates frequencies.
  • The phase response curve, which describes how the system delays frequencies.

The impulse response describes how the system reacts to an ideal impulse. An ideal impulse is also known as a Dirac impulse. This representation allows us to visualize the time of arrival of the different signals.

The following sections will provide detailed information on how to set up for the best possible results.

The behavior of the session system will be explained in order to help you organize your work, and how the IO relates to this specific layout.

Then, we will discuss the two main scopes used in the layout: the transfer function and the impulse response.

Of course, we will also explain the structure of the user interface and how to work efficiently inside this system tuning page.

  1. A linear and time-invariant system must meet two criteria: the processing of signals x and y must be the same as the sum of their individual processing (linearity), and the processing of a signal at any given time must always produce the same output (time invariance). Rooms, reverb units and speakers generally function linearly. However, compressors, saturators and limiters do not. Chorus, tremolo, vibrato, and modulation effects are not time-invariant. See more.↩︎