Sessions & Captures System

Introduction

MiRA:: has a very complete system for managing all the measurements done by the user. Inside the application, a measure is called a capture. A capture contains the channel’s spectrum, transfer function and impulse response. Captures are organized per session. Each session is materialized by a .fcap file inside the following folders:

  • ~/Library/Application Support/FLUX/MiRA/Captures on macOS
  • C:\User\/...\AppData\Local\FLUX\Captures on Windows.

A session can serve to multiple purposes. It can represent the measures of the sound system of a venue or of a specific audio equipment. It can also serve to store calibration files or target curves.

Note

MiRA:: can import a wide variety of calibration and measure files from other manufacturers.

For system tuning, the main workflow strategy of MiRA:: is to allow very quick system measurement while giving you all the tools to work and recompute offline.

To accomplish the on-site measurement, you can use pink noise to calibrate the delay finder algorithm, then use a few sweeps to measure what you need to measure (heads, subs, front-fields, etc.). Note that MiRA:: has its own signal generator to simplify the process.

Once the captures are acquired, MiRA:: can recompute delays, average, acoustic sums and so on without having to keep playing sounds through the sound system

Quick start to captures

I/O setup

The first step of any capture process is to make sure that the I/O is correctly configured. Go to the IO menu, by reaching either the info header, or to the top menu Mira>IO settings on macOS, or Files>IO settings on Windows.

Make sure to select the right input and output audio interface. Then, you must configure the different input channels of the capture system. In the case of this example, the number of microphones is set to one, then the first line of the table is set to input channel one and as the transfer function reference. The second line of the table is set to input channel two and as a microphone input.

With these settings, our reference signal will be detected on input channel one and our measurement will come in input channel two.

We also need to make sure that the signal generator is correctly patched. In our example, we want the signal generator to output on channels one and two. Same signal is outputted on both channels, it simply makes the next part of the routing easier. The output 1 of our audio interface is looped back to input 1. The output 2 goes to our system, and the output of the system goes to input 2 of our audio interface.

At this point, our whole routing is set up.

Creating a session

The very first step is to create a new session to store our captures. Simply click on the “new session” button. A popup appears to ask you to name the session. Name it accordingly and press OK.

Checking for delay offset

It is absolutely crucial to make sure that all your microphone inputs are properly aligned with the reference signal. In MiRA::, the recommended method is to set the signal generator to a pink noise and start it. If our previous routing is good, we should now see some time offset appearing in the \(\delta\) column of the system.

You can apply these delays by clicking on the button.

Acquiring the capture

It is of first importance to understand that there are two main ways to create captures:

  • You can send any signal into the system to measure, then create a capture when the curves have stabilized.
  • You can automate the capture to the emition of a sweep tone.

Most of the time, it is preferred to use an automated sweep tone to realize the measure. In MiRA:: we simply have to click on the icon. Each time, MiRA:: will ask you to name the capture.

Repeat the process for each measure that you need to create (different loudspeakers, heads, subs, front field, etc.).

Capturing online, processing offline

In the previous section, we have seen many parameters related to the different input channels. It is very important to understand that none of them are permanently bound to the measure itself. You can always modify the applied delay, capture & target curves, microphone pairing and gain.

The computation curve itself is automatically regenerated based on the modification made to the captures. The main idea is, as stated above, to captures online and to process offline. In other words, most of the system tuning job can be done without being tied to the PA system itself.

Offline settings

Captures menu

Captures menu

All the offline adjustments and settings are done in the capture menu. Because they are identical to the System Setup menu settings, please refer to this part of the user documentation.

Computation curve and sessions

A session can have as many captures as the user want, but only one computation curve. It is because the computation curve is dynamic, depending on which captures are affected to it, the time alignment between them, and so on.

Still, it is possible to store the current state of the computation curve to a new capture, to keep track of your improvement, to access quickly to different computations or to store them as target curves. To capture the computation curve, click on the Capture Computation Curve button.

Changing capture settings

By default, newly created captures follow the settings of the transfer function. If you want to change the spectrum type, block size or time averaging afterward, you can use the “Update capture setting” option in the “Capture” menu in the top menu of the application.