Specifications

EAW Smaart 6 Operation Manual Concepts, Glossary, and Bibliography

• At frequencies where the measurement signal has more energy than the reference

signal, the transfer function is a positive dB value; when the measurement signal

has less energy, the value is negative.

• With respect to the input level meters and the default Full-Scale calibration

reference, 0 dB (or 0 dBFS) means the maximum possible output of the A/D

converter on the selected input device. All lesser amplitude/magnitude values

are displayed as n dB down from this maximum.

2.1.2 Fast Fourier Transform

The Fast Fourier Transform (FFT) is a special case of Discrete Fourier Transform

(DFT), a mathematical technique used to calculate the frequency-domain representation

of a finite length, time-domain data series. The output of a Fourier Transform is a set of

complex numbers representing the frequency and phase of the original time series. An

FFT is referred to as a Fast Fourier Transform because it uses mathematical shortcuts

to greatly reduce the computation time required to calculate a DFT. This technique requires

that the time-domain data series used in the FFT contain a power of two number of sam-

ples (i.e., 2

samples, where n is an integer). All Smaart 6 frequency transformations

are FFTs that require the time record to be 2

samples in length.

Table 2-2 Powers of 2

NOTE: It is certainly possible to calculate the Fourier Transform of a time record with

an arbitrary number of samples. However, when the number of samples is not

a power of 2, the additional calculations required on a PC can become very

large, sometimes resulting in a very slow Fourier Transform.

256

9512

10 1024

11 2048

12 4096