Specifications

EAW Smaart 6 Operation Manual Concepts, Glossary, and Bibliography
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2.1.3 Averaging
When using asynchronous test signals such as music or random noise in FFT measure-
ments, it is often beneficial to average data from a number of FFT frames. Averaging
over a number of FFT frames:
• increases the likelihood of having sufficient energy at all frequencies for a
meaningful measurement (particularly with music);
• makes the overall frequency content of a dynamic signal easier to see;
• helps minimize the influence of possible sources of error that might affect a
single FFT measurement.
Nearly all Smaart averaging is based on RMS averaging, aggregated either linearly (all
frames contribute equally to the averaged result), or exponentially (more weight given to
the most recent, than to older data). Linear averaging is also sometimes referred to as
artithmetic averaging. Smaart offers linear averaging options from 1 (no averaging) to 128
frames. There is also a linear infinite averaging option that keeps a running average while
the analyzer runs (or until you Reseed the averaging buffer). The Fast and Slow aver-
aging options, available for Spectrum and SPL measurements, are exponential averages.
2.1.4 Sampling Rate
The sampling rate is the number of amplitude samples taken per second from an analog
audio signal to create a digital waveform. The most important thing to remember about
sampling rate is that it limits the highest measurable frequency. The highest frequency
that can be accurately represented in a digital waveform is equal to half of the sampling
rate. This limit is often referred to as the Nyquist frequency, after Harry Nyquist who
first proved its existence in the course of his work on improving the speed and carrying
capacity of telegraph and teletype systems in the early 20th century.
If frequencies in excess of the Nyquist frequency are present in a signal when it is digitized,
they become aliased or wrapped around and incorrectly added in at lower frequencies.
For this reason, a high-order low pass filter with its corner frequency near the Nyquist
limit is normally applied to audio signals before they pass through an A/D converter.
The practical implication of this anti-aliasing filter is that it further limits the highest
measurable frequency at a given sampling rate, typically to about 90% of the Nyquist
frequency.
Compact discs run at a standard sampling rate of 44.1 kHz. Professional digital audio
recording machines sample in the range 48-96 kHz. Computer sound cards commonly
have several user-selectable sampling rates such as 48, 44.1, 22.05, or 11.025 kHz.
Smaart 6 determines the available sampling rates by polling your computer’s sound
hardware each time it launches. The fastest sampling rate supported by Smaart 6 is
currently 96 kHz.