Teac GX-1, Инструкция по эксплуатации

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Amplifiers
4-21
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Analog Playback
In reproduction using the analog output amp AR-GXAO, the
instantaneous value input is output as the instantaneous value
without change. ±100% of the input for the selected input
range is output by the voltage selected in Output Range.
Example
When you set 1.0 V in Output Range of the analog output amp,
±100% of the input, using instantaneous values, for the selected
input range (by using the AD conversion value, ±25000) is gen-
erated by ±1 V.
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Waveform Display Window
In the waveform display window, the instantaneous value
(peak-to-peak) is displayed. The upper and lower two grids
correspond to ±100% of the input, using instantaneous values,
for the selected input range. The display range is ±131%.
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FFT Window
With 0 dB as the scale of the Y axis on the FFT window,
±100% of the input, using instantaneous values, for the selected
input range is displayed.
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To Convert Data to RMS Values
Sound is a compressional wave, and microphone output is a
plus value in a dense location, and a minus value in a sparse
location. Data recorded to GX-1 is unchanged instantaneous
values.
A recorded AD conversion value is an integer from –32768 to
+32767. ±100% of the input, using instantaneous values (peak-
to-peak), for the selected input range is converted to an AD
value of ±25000. To convert this AD conversion value to a
physical quantity, you multiply the AD conversion value by the
SLOPE value of the header file.
To convert an AD value to the instantaneous sound pressure
value in Pa units, use the following formula:
Instantaneous sound pressure (Pa)
= AD conversion value x SLOPE
To express this instantaneous sound pressure as an absolute
value in dB units:
From 20 µPa = 0 dB,
Sound pressure (dB absolute value)
= 20 log (
|
instantaneous sound pressure value (Pa)
|
/ 0.00002)
To convert the instantaneous sound pressure to rms (root-mean-
square) values in dB units, use the following formula:
Sound pressure (dB rms value)
= 20 log [(square root of the one-cycle average of squared
individual instantaneous sound pressures) / 0.00002]
While treating the waveform of one cycle as a sine wave, to
perform a quick conversion of instantaneous sound pressure to
an rms value in dB units, use the following formula:
Sound pressure (dB rms value)
= 20 log (
|
instantaneous sound pressure value (Pa)
|
x 0.707 / 0.00002)
Example
For this example in which recording used an input range of 120
dB, we want to calculate the number of dBs for the rms value
for ±100% of the input, using instantaneous values, for the
range. When the input range is set to 120 dB, the SLOPE value
of the header file becomes 0.0008. ±100% of the input is con-
verted to an AD value of 25000.
The instantaneous sound pressure value (Pa) is the AD value
multiplied by the SLOPE, so the result is:
|
±25000
|
x 0.0008 = 20 (Pa)
If you express the above as an absolute value in dB units, the
result is:
20 log (20 / 0.00002) = 120 (dB)
If you perform a quick conversion of the instantaneous sound
pressure to an rms value in dB units, the result is:
20 log (20 x 0.707 / 0.00002) = 117 (dB)