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Sound Perception and Acoustics

12/03/2018, Author: Audio Academy

In discussions among most sound enthusiasts on the various ways to improve the quality of audio production and audio mixes, the focus tends to be on the gear and process. However, it is just as important if not more to consider the conditions under which sound is perceived by the average listener.
These conditions are:

REVERBERATION

Reverberation refers to the time it takes for the sound to die down after the source of the sound has stopped. Reverberation is crucial to giving the listener a sense of space and localising sound. When a sound wave meets a new surface boundary of a material, some energy is absorbed and some is reflected. The material’s surface structure impacts the absorption as well as direction or angle of the reflection. The more reflective the surface walls of a room, the more reverberant the space will be, as the reflections bounce off the wall until their energy is eventually absorbed. Sound will reflect off the surfaces, and with each reflection there is a change in timbre and amplitude (as some frequencies are absorbed and others are reflected).

A room can be treated with a combination of absorbent and reflective materials based on their absorption coefficient. This allows for a more honest listening experience that favours critical mixing decisions for an engineer.For the average listener, a treated room will give them the experience of listening to a mix in the most balanced way.

An engineer, by using reverberation effects on sounds,can simulate the effect of being in a real space such as a concert hall, an underground bunker or an empty garage.This can greatly enhance the experience of listening to a mix.

STANDING WAVES

For people who love singing in the bathroom, you might have had the experience of certain notes making the whole room resonate. This note is probably one of the room’s standing waves. A standing wave is a low frequency resonance that is created between two parallel walls as the reflected wave interferes constructively with the incident wave. The resonant frequency depends on the distance between the two parallel walls.

These standing waves can alter the perception of sound often creating an imbalance by overemphasising certain frequencies in the mix that match the dimensions of the room.Such resonances cannot be absorbed. A listening environment with little to no parallel surface can mitigate unwanted resonances in a room.

LOUDNESS

A little know but very important factor that can drastically affect perception is the loudness level of the playback system. As evidenced by the Fletcher-Munson curve or the Equal Loudness Contours, when we listen to sound at a low volume our ears favour mid frequencies. This makes them seem louder in comparison to high, as well as low frequencies. At louder volumes our perception tends to be less skewed. This does not mean that we should listen at the highest level possible, doing that can lead to long term hearing damage.

What we can infer from the curves is that an average listening level of 85 dBSPL measured with a C weighting curve is the apt loudness level for a reasonably balanced listening experience. This level would be just slightly louder than conversational level which is about 70-80 dbSPL.

Factors such as room resonance,reverb and the listening level need to be addressed first before trying to judge the effectiveness of any piece of audio gear or approach to a mix.The have a undeniably significant impact on the way we hear but are often taken for granted.

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