09 - Sound Level Meters Flashcards
Do you need a coupler when measuring a sound field?
No - measure using the appropriate microphone
What are some important components of the SLM?
Weighting networks (A, B or C)
Filters (frequency specific SPLs)
RMS Detector
dB RMS = _____% of the peak amplitude
70.7
The dB RMS makes all values of a waveform _______ (positive/negative)
Positive
A SLM measures dB RMS either fast or slow. State the rate for each
Slow: RMS measured every 1 second
Fast: RMS measured every 1/8th second
Why might we measure a sound (using an SLM) to be 90 dB, but perceive it to be quieter?
Our ears are more sensitive to some sounds than others
-> Equal loudness curve (shows what dB is needed to perceive each frequency the same)
True or false: Weighted filters on an SLM are applied to make a sound more perceptually relevant
True
If a weighted filter was used, how do we write the recorded sound?
x dBA (where A is the class of filter) *do not write SPL
Which class of weighted filters shows more attenuation (less gain) in the low frequencies?
A-weighted filter
Which class of weighted filters shows the least amount of attenuation (gain closest to 0)?
C-weighted filter
True or false: filter bank analysis allows us to get to know the sound in a frequency specific manner
True
What are the two most common types of filterbanks?
Octave and 1/3 octave
What defines a constant percentage bandwidth filterbank?
The bandwidth of the filterbank is a constant percentage of the centre frequency
(e.g. octave filter bank bandwidth is 70% of central frequency, 1/3 octave is 23-24%)
What equation do we use to find the lower frequency cutoff?
F(L) = F(C) / 2^(1/2N)
What equation do we use to find the upper frequency cutoff?
F(U) = F(C) x 2^(1/2N)
