Sound, PA systems and acoustics are a huge subject. For those out there who are interested in furthering their knowledge, here are a few pages that may encourage or help. They are targeted at those with intermediate knowledge or beginners. For those wishing to go further, we highly recommend The Sound Reinforcement Handbook. You can purchase the book by clicking the link. Or you can search for other books about sound engineering.
Click on the headings below to expand each article.
Perception of loudness is a complicated subject. Every person will perceive loudness differently, as everyone’s ears are different. In fact, everyone’s ears have a slightly different frequency response.
This is why, in sound engineering circles, there is a need to quantify sound pressure levels to define what is loud, and what is quiet. Or perhaps that should be; what is too loud and what is too quiet. The unit of measurement is the dB SPL (decibel). There are also more accurate measurements of loudness called phons, and subjective loudness, called sones, but these are rarely used and are outside the scope of this course!
For convenience we normally measure dB SPL from the mix position, but it can be useful to measure from other areas such as the front row and the stage.
For those new to dB SPL here is an idea of how different sounds compare in level:-
|Recording studio||30dB SPL|
|Conversational speech||60dB SPL|
|Noisy office||80dB SPL|
|Church concert (contempory worship)||95dB SPL|
|Loud rock concert, front row||120dB SPL|
|Threshold of pain, average young person||130dB SPL|
|Concord take-off from runway side||140dB SPL|
|.357 Magnum handgun, (peak impulse)||165dB SPL|
|Under a Saturn 5 Rocket on take-off!||194dB SPL|
To make things more complicated, perceived loudness varies with frequency – a low frequency sound of the same measured intensity will sound quieter than a mid-range frequency sound. The dB SPL (A) weighted scale is designed to help compensate for this.
Running a successful sound check is mostly about proper preparation. If you have a similar band and a similar set-up in the same venue each week, you are fortunate, you have all the time in the world!
A sound check is 80% getting the stage sound right for the band, and 20% getting it right for the front of house. Front of house mixing is much quicker and easier, as you only have one mix and only your own ears to please (for now), but the band could have 4 or more mixes and all kinds of preferences.
We get asked this all the time, and we're afraid that there is no very short answer (other than “turn it down!”). However, there are steps that can be taken to greatly reduce the risk of feedback. Reduce the risk almost to zero in some circumstances.
Compression is an essential tool in modern sound engineering. Most commercial recordings will have compression on just about every instrument. In the world of live sound, many amateurs do not correctly understand the best use for compression.
Compression should be used in the first instance to help achieve a sound without harsh or unexpected peaks that cut though and ‘grate’ on ones ears. The human ear is actually more sensitive to these mid-range frequencies. The main culprit here are vocals. This is because vocals have a lot of mid-range frequency content, and because singers (even good singers) often unintentionally vary the distance from their mouth to the microphone, effectively giving their voice even greater dynamic range.
Adding compression limits the dynamic range, evens out the small variation in microphone position, and provides a smoother sound for the audience. You can achieve a similar effect by ‘riding’ the fader on the vocals and listening, but it’s pretty hard work, and the singer can catch you out.
It’s important to remember that using a compressor on an insert will affect the signal sent to the monitors as well. Too much vocal compression may be annoying for an experienced vocalist who expects the monitor to get louder as they approach the mic. Although, in the case of an experienced vocalist, less compression (lower ratio) is normally needed to reign in the sound!
Use of the attack and release controls can change the way the compression behaves. It takes a while to become familiar with the effect of the controls, and with what works and what doesn’t. In most cases, a fairly fast attack and a medium or slow release is the way to go. We would suggest you leave your compressor set on auto if it has this feature, and if not, leave the controls at 12 o’clock!!
Compressors can be used for a variety of other applications, even across a whole mix. This can have un predictable effects – in general it’s best to restrict the use of compression to a few key channels, unless you really know what you’re doing!
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