Specifications

EAW Smaart 6 Operation Manual Analysis Modes and Display Types

Smoothing

Smoothing, an averaging technique available only for Frequency Response measurements,

can reduce the jaggedness of the Magnitude trace, making trends in the system response

easier to see. Smoothing averages each data point with a number of adjacent points on

either side of it determined by the Smooth setting below the Freq. Resp. button. The

Smooth settings available from the drop-list are none, 3, 5, 7, 9.

For example, if Smooth = 3, each data point represents the value of that point averaged

with the next higher and next lower points on the trace. If Smooth = 5, each data point

represents the value of that point averaged with the two higher and two lower points on

the trace. In other words, you are averaging across frequencies, effectively increasing

the bandwidth of each frequency data point rather than over time as in the case of RMS

and Vector averaging.

3.2.7 Coherence and Coherence Blanking

Coherence Overview

Coherence is an indication of the linearity between two signals in a Frequency Response

measurement. The Coherence function basically asks “What are the chances that the

signal that went into the system became the output signal that we got back as a result of

a linear process?” The answer is returned in the form of a probability value between 0

(no confidence) and 1 (perfect certainty) for each frequency data point. Smaart converts

coherence values to percentages for display purposes, where 100% = perfect coherence.

Although values closer to 100% generally mean higher linearity and better data, it is

important to note that low coherence values do not necessarily mean the data is untrust-

worthy. For example, making acoustic measurements in noisy environments requires

significant averaging, which naturally decreases coherence. Since some of the same

factors that encourage using more averaging, such as ambient noise, also lower coherence,

these factors have a combined effect.

In real-world measurement situations, good coherence can be relative, so it is often

more useful to look for overall trends in the coherence of a measurement than for specific

coherence values. If some frequencies have much lower coherence values than most

other frequencies, you should be skeptical of these results and more confident of the

frequencies closer to the general trend line.

Additional factors that can adversely affect the coherence of Frequency Response data

include: delay between the two signals, insufficient energy in the reference signal at a

given frequency, acoustical influences (i.e., reflections, modes and reverberation), and

ambient or electrical noise. Nonlinear processors such as compressors and limiters in

the measurement signal path can also have a negative influence on coherence and

should be bypassed for Frequency Response and Impulse Response measurements.