Simulating Space – Part 1: Analogue

As long as music has been recorded, musicians and producers have been trying to put the space back into recordings, and in this series of posts I will discuss how music makers have tried to recreate the reverberant properties of a space and how we are now able to model the acoustic properties of spaces which sadly no longer exist.

reverb1
Rough diagram demonstrating how reverberation is made up of acoustic reflections

First things first though, I should talk about how reverberation works in a space. Sound waves travel through a space and are reflected back to the listener’s ears. The first few times this happens the individual echoes are distinct but subsequently they begin to blend together, with different frequencies reinforcing and cancelling out each other to create the timbre of the reverb.

reverberation
Idealised diagram showing the decay of reverberation over time. I promise this will get more interesting in the future

The first attempts, in the age of the gramophone were in many ways the simplest and most obvious: Build a very very reflective room, put a speaker at one end and a microphone at the other and record the sound you got. It’s not hard to see how this wasn’t a great solution, the sound quality is capped by the poor fidelity of speakers at the time and all the recordings treated this way will tend to sound like they were all performed in the same bathroom.

In 1935 Laurens Hammond, at the same time as inventing the first reliable electro-mechanical organ, developed a device to try and give a sense of ambience to the living rooms and small churches his new invention found itself in. In this method an electrical signal hits a transducer that sends actual sound down a series of springs and into a second transducer to turn the sound back into an electrical signal. This signal is then mixed back into the original sound to create the complete effect. A similar technique uses a bloody great sheet of metal to produce the reverberation effect and is known as Plate Reverb. Crucially, neither of these techniques need a dedicated room for their ambience and so tended to be more popular in newly built studios.

The commercial development of magnetic tape in the late 1940’s; as well as just being generally transformative of the recording of music and enabling everything from overdubbing, editing, sampling, retaking bad performances and backmasking to hide the satanic messages that are in all the best pop music; using the same method to permanently record music to play back sounds just a few hundred milliseconds after it was recorded to produce a discrete echo sound before erasing the tape sound in preparation for new sound to be recorded on to the same tape. Listen to any early Elvis song and you can hear the quick “slap-back” echo developed at Sun Records. Later devices would use multiple playback heads to attain a more reverb-like effect. A combination of these techniques, tape providing the pre-delay and spring or plate providing the later reflections formed the first simulations of room sounds.

diagram
Simplified diagram of tape recorder. The pale blue circle is a permanent magnet that erases the sound stored on the tape

So that would be the end of it, right? Of course not, of course it’s more complicated than that. Because it turns out that reverberation is also frequency dependent as well, with higher frequencies tending to tail off faster than the low-midrange frequencies. Except when they don’t, because the materials of the spaces are dense and highly reflective. There is no way to build an electro-mechanical delay line where you are able to tailor the frequency response without a separate delay line for each frequency band. Not only that, but every one of these electro-mechanical methods have their own frequency responses that must be taken into account when playing the sound back. The mathematics that govern how sound waves interact are hugely complicated and it would take a specially designed machine to calculate everything needed to approach the actual sound of a place.

Fortunately in 1943 a chap called Tommy Flowers designed a machine that was very good at doing hugely complicated maths and over the next 40 years engineers managed to make it smaller than a bus. Now producers were able to digitally emulate all of the above techniques for producing ambience as well as beginning to model the response of spaces to various sounds.

NB: Further backing up David Byrne’s characterisation of recorded music as its own space that shapes sounds artists have taken these methods and used them as interesting sounds in their own right. Entire genres from dub to surf rock to ambient electronica have been built around these techniques. Some people have even made an entire career out of these artificial echoes.

Further listening:

Mystery Train – Elvis Presley. One of the first examples of magnetic tape to produce an artificial echo.

Miserlou – Dick Dale. I could have chosen almost any surf rock song to show the sound of spring reverb. Not many of them are also a middle eastern folk song though.

The Supernatural  – John Mayall’s Bluesbreakers. Would you believe this wasn’t recorded in a really big room? Probably. Still, it’s a good example of the sound of a plate reverb.