Bottling Air: Genelec and The Art of the Impulse Response

Blog Post by Sound Engineer Kyle Pyke

If there is one thing I’ve learned on this trip, it’s that the proprietors of religious spaces love the sound of their hall. It doesn’t matter if it’s an ornate Gothic cathedral, or a dilapidated Romanesque parish-- for those charged with preserving their edifice, it’s an everlasting source of pride.

The reflections and resonances of each space are as unique and beautiful as the adornments within, and fundamentally what we try to capture during each recording. While there is no way to take the venue with us when we leave, we have a way to save its essence. If we measure, at every frequency in the spectrum of human hearing, how a hall reacts to a stimulus, we can digitally recreate that space. The result of this test is called an impulse response (IR).


I’ve commented before on the necessity of accuracy in the recordings we do, and this is no different. If a stray signal (a dog bark, footsteps, a clock chime, etc.) makes it into our measurement, the digital model of the space is no longer viable. Similarly, if the measurement signal is not reproduced accurately, certain sonic frequencies may be over or under represented as a natural limitation of the equipment.

Knowing that we were recording in spaces we might never see again, I wanted to make sure we had an impulse response of as many of the venues as possible. Genelec was my first choice and contact. Their loudspeakers can be found in nearly every recording studio worldwide, and are the standard for the measuring impulse responses.

Genelec was kind enough to lend us two 1037C loudspeakers (pictured above), which contain three amplifiers- one each for low, medium, and high frequencies. Since a high frequency has completely different energy requirements to a low frequency, having a separate amplifier for each range makes for a very clean measurement. Additionally, these speakers have excellent projection to the sides. Many of our sessions are in very wide spaces, and making sure that we’re able to record the measurement from all angles creates a more natural impulse response, when we recreate the space later.

Here is a demo of the IRs we've been making. Below is the beginning of the familiar G-major prelude, completely dry with no room-sound whatsoever.

Here is the exact same audio recreated in La Iglesia San Martin in Fròmista, using an IR we sampled from the hall:

Toward the end of this trip, we will be releasing an application that will allow you to listen to the suites in any of the halls where we have taken IR measurements.

Happy Trails!