Equalization

One of the most powerful tools for increasing the potential acoustic gain of a sound amplification system is the production of a "mirror image" filter to level the frequency response of the system. The process of equalizing an auditorium also improves the fidelity of the sound. The process of leveling out the frequency response of the sound system removes the peaks which will ring the system before sufficient gain is achieved.

Equalization Process

The basic idea of room equalization is for the sound system to produce in the room exactly the same signal which is put into the system. So if you put pink noise in and get pink noise out, you are close to that goal. A real-time analyzer can be set so that a pink noise input produces a straight horizontal line on its display. With pink noise input, the equalizer is then adjusted to get a straight line output. The sound system is then equalized to the room.

White Noise

For processes of testing and equalizing rooms and auditoriums, it is convenient to have broad-band noise signals. Typically, white noise or pink noise is used. 对于房间和礼堂的测试和平衡过程，使用宽带噪声信号是方便的。通常使用白噪声或粉噪声。

Representing the differences between white and pink noise in dB makes the difference seem less drastic. 用分贝表示白噪声和粉噪声的差异，会使这种差异显得不那么剧烈。

Pink Noise

Pink noise, rather than white noise, is often the choice for testing and equalizing rooms and auditoriums. Broad-band noise signals are desirable for such testing. 粉红噪声，而不是白噪声，常被用于测试和校准房间和礼堂。宽频带噪声信号对于此类测试是理想的。

Whereas white noise is defined as sound with equal power per Hz in frequency, pink noise is filtered to give equal power per octave or equal power per 1/3 octave. Since the number of Hz in each successive octave increases by two, this means the power of pink noise per Hz of bandwidth decreases by a factor of two or 3 decibels per octave.

Since pink noise has relatively more bass than white noise, it sounds more like the roar of a waterfall than like the higher hissing sound of white noise.

When pink noise is chosen for equalizing auditoriums, real-time analyzers can be set up so that they display a straight horizontal line when they receive pink noise. With pink noise input to the sound system, the response curve can be adjusted to produce pink noise in the auditorium as measured by the real-time analyzer. This provides optimum fidelity as well as increases the potential acoustic gain of the sound amplification system.

With pink noise, the intensity is filtered to drop 30 dB over the 10 octave audible frequency range. 在粉红噪声中，强度被滤波处理，使其在10个 octave的可听频率范围内降低30 dB。

The difference between pink noise and white noise is exaggerated in the top illustration by the process of making the vertical axis linear with intensity. The reason is that the ear is definitely not linear in its response to sound. The sound intensity of pink noise drops by a factor of 1000 over the audible frequency range, and that sounds very drastic. That drop should be considered in light of the "rule of thumb" for loudness perception: the fact that dropping the sound intensity by a factor of 10 or 10dB results in a sound that is perceived to be half as loud to the human ear. If each 10dB of drop results in a sound half as loud, then a 30dB drop will result in a sound perceived as 1/8 as loud - significantly less, to be sure, but not as drastic as the factor of 1/1000 in intensity would imply.