SP395 SoundPro Audio Integrator
Form7492
Operation Manual
35
FFT Analyzer
The SP395 FFT Analyzer function processes the audio received at the microphone or left line
input through three cascaded FFT stages that resolve the audio spectrum into octave, 1/3, 1/6, or
1/12 octave bands. Compared to the filter-based RTA (above), this function is slower to update,
but has much finer frequency resolution.
Each band is graphed as a vertical bar, with the height representing the SPL level of the
individual octave or sub-octave bands within the audio spectrum. The graph displays either a 30
dB or a 15 dB range. The display is updated approximately twice per second, with selectable
signal averaging times from 1 to 60 seconds.
The internal signal generator can be used
to provide pink noise while using the
FFT Analyzer function. FFT Analyzer
graphs can be stored and recalled for
viewing and analyzing at a later time,
and the data can also be sent to a
computer.
Use the SP395 FFT Analyzer function to
analyze the frequency response of audio
systems and listening rooms, and to
monitor the results as you re-position
speakers, adjust room treatments, and
change equalizer settings for the most
acceptable response.
FFT Analyzing Test Screen
FFT Display and Control Fields:
1.
Test Function
- Identifies the test function (FFT)
2.
This field is empty on the FFT screen. No selection
3.
Graph
Resolution
- Click the dB number at the top of the left graph axis to change the
vertical graph resolution between 1 dB/pixel (30 dB range) to 0.5 dB/pixel (15 dB range).
The resolution number changes to be either 30 or 15 dB higher than the range number at
the bottom of the axis.
4.
Run/Pause –
Start the FFT or pause it by clicking the Run/Pause
field. Pause the test to
"freeze" the displayed FFT graph so that you can easier make cursor measurements or
store the graph to memory.
5.
Octave Mode –
Select octave or sub-octave band. Select octave, 1/3 octave, 1/6 octave,
or 1/12 octave bands, as indicated by Oct, 1/3, 1/6, or 1/12.
6.
Averaging –
Select an exponential decay averaging mode with a time constant of 1, 3, 6,
10, 30 or 60 seconds; a mode that averages equally over time (cumulative); or peak hold
mode. A numeric value indicates an exponential decay mode, with a time-constant equal
to the value. Exponential decay averaging means that more recent sounds have more
bearing in the displayed average. A longer time constant produces a more stable display,
but a slower response to changing sounds. Cumulative average mode is indicated by
AVG. Peak hold mode is indicated by HLD.
7.
Overlay Test Filter
– Select Flat response (normal), the A or C weighting curve, or the
difference (Diff). Note that these overlay filters actually modify the data on the screen,
