Digital Sound & Music: Concepts, Applications, & Science, Chapter 4, last updated 6/25/2013
noise into the room. The commercially available portable isolation booths typically have
ventilation systems available that do not compromise the isolation and noise level for the booth.
If you're putting in a ventilation system for a large studio, be prepared to spend a lot of money
and hire an expert to design a system that meets your requirements. In the worst-case scenario,
you may need to shut off the ventilation system while recording if the system is creating too
much noise in the room.
There are differing opinions on acoustical treatment for the studio. In the room where the
actual performing happens, some like a completely acoustically dead room, while others want to
have a little bit of natural reverberation. Most studios have some combination of acoustic
absorption treatment and some diffusion treatment on the room surfaces. The best approach is to
have flexible acoustic treatment on the walls. This can take the form of reversible panels on the
wall that have absorption material on one side and diffusion panels on the other side. This way
you can customize the acoustics of the room as needed for each recording.
In the control room where the mixing happens, you don’t necessarily want a completely
dead room. You do want a quiet room, and you want to remove any destructive early reflections
that arrive at the mixing position. Other than that, you generally want to try to mimic the
environment in which the listener will ultimately experience the sound. For film, you would want
to mimic the acoustics of a screening room. For music, you may want to mimic the acoustics of a
living room or similar listening space. This way you're mixing the sound in an acoustic
environment that allows you to hear the problems that will be audible by the consumer. As a rule
of thumb, you should design the acoustics of the room for the best case listening scenario for the
consumer. Then test your mix in less desirable listening environments once you have something
that sounds good in the studio.
4.3 Science, Mathematics, and Algorithms
4.3.1 Deriving Power and Voltage Changes in Decibels
Let's turn now to explore more of the mathematics of concepts related to acoustics.
In Section 2, Table 4.2 lists some general guidelines regarding sound perception, and
Table 4.5 gives some rules of thumb regarding power or voltage changes converted to decibels.
We can’t mathematically prove the relationships in Table 4.2 because they’re based on
subjective human perception, but we can prove the relationships in Table 4.5.
First let’s prove that if we double the power in watts, we get a 3 dB increase. As you
work through this example, you see that you don’t always use decibels related to the reference
points in Table 4.3. (That is, the standard reference point is not always the value in the
denominator.) Sometimes you compare one wattage level to another, or one voltage level to
another, or one sound pressure level to another, wanting to know the difference between the two
in decibels. In those cases, the answer represents a difference in two wattage, voltage, or sound
pressure levels, and it is measured in dB.
In general, to compare two power levels, we use the following:
( *
Equation 4.15
If then we have
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