Monitor Audio ASW100 User Manual download pdf (Page 187)

Audio Analyzer

AM700 Audio Measurement Set User Manual

4-75

Input Filtering

The AM700 provides several weighting and bandwidth limiting filters. Weighting

filters are designed to provide measurements that correlate better with human

perception than do unweighted measurements (not only is human ear sensitivity not

flat with frequency, but human ear frequency response varies with the amplitude of

the sound level). Not all weighting filters are identical. Each filter is an approxima-

tion to the sensitivity curve of the ear under certain conditions. Filter characteristics

are defined by various audio standards organizations. Refer to documentation

provided by these organizations for more information on use of a particular

weighting filter.

While bandwidth-limiting filters have flat frequency response over the center part of

the audio band between their lower and upper roll-off frequencies, weighting filters

have no flat-response characteristics. AM700 filter selections are: CCIR468, CCIR

ARM, A Weighting, F Weighting, B Weighting, C Message, C Weighting, 15 kHz

Low-Pass, 20 kHz Low Pass, 22 kHz Low Pass, and 400 Hz High-Pass. Curves for

these filters are illustrated in Figures 4-33, 4-34, and 4-35. The curves for the 15, 20

and 22 kHz Low Pass filters are similar; the only difference is the location of the

–3 dB roll off frequency.

The most common bandwidth for noise measurements in professional audio,

broadcasting, and consumer audio applications is 20 Hz to 20 kHz (or 22 Hz to

22 kHz, as specified in CCIR 468). Certain communications applications typically

specify a narrower bandwidth for communications-quality voice: 300 Hz to 3.5 kHz.

The various weighting filters produce the require response curves for noise testing in

these specialized bandwidths.

To specify an input filter do the following:

H Press and hold the Filter button to display the Filter menu. In this menu you can

choose an input filter for either input channel from a pop-up list.

H Touch the Channel 1 or Channel 2 soft key to bring up the pop-up list of filters

for that channel as shown in Figure 4-32. (Touch the Filter front panel button to

permit access to the soft keys if they are grayed out.)

H Turn the control knob to select the desired filter (or choose None to choose no

filter).

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Monitor Audio ASW100 User Manual Page 187