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Microphone Preamplifier
type PA14
For use with a multimedia computer
using a SoundBlaster compatible soundboard, e. g. a SoundBlaster
Live! Player 5.1 board, and software for speech and voice analysis.
Hardware:
The preamplifier PA14 is low-cost high-quality
general-purpose preamplifier intended for use in speech analysis
in connection with a standard multimedia computer or a computer
equipped with a standard sound board with loud speakers.
Normally, a multimedia computer is supplied
with both a microphone and a line input. How-ever, the sensitive
microphone circuit picks up noise from the computer because the
electrical noise level inside a computer is very high. Therefore,
it is not recommended to use a microphone connected to the microphone
input. Instead, always use the line input. However, as the sensitivity
of the line input is less than the sensitivity of the microphone
input, it is necessary to amplify the microphone signal. Therefore,
an external microphone preamplifier is necessary. Because of the
reduced noise level, when using a preamplifier, the dynamic range
will be increased with 15 dB in most computers.
The preamplifier PA14 takes advantage
of the fact that the soundboards mentioned are intended for stereo
sound recording, thus having two independent channels. In this
way it is possible to record, sample, and store two simultaneously
recorded signals in the computer. The preamplifier uses the left
channel for the microphone input and the right channel for an
analyzer input which could be e.g. an electroglottographic or
airflow recording. In this way it is possible, simultane-ously,
to have both an acoustic registration and a physiological registration
of voice and speech.
The human voice covers a great dynamic
range from about 35 to 125 dB SPL. This range is greater than
the normal dynamic range of electronic amplifiers, tape recorders,
sound boards etc. Therefore, the preamplifier PA14 has six overlapping
dynamic ranges 0, 10, 20, 30, 40, and 50 dB SPL. The ranges are
selected by a rotary switch. The amplifier is supplied with a
semi-variable gain control used for presetting the microphone
gain over a 20 dB range (preset at delivery to 14 dB). PA14 is
well-suited for use in connection with software for phonetography.
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| Specifications for type PA14
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| Microphone: |
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| Recommended microphone: |
AKG type D190E (dynamic cardioid microphone).
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| Microphone sensitivity: |
0.23 mV/µB at 1000 Hz. |
| Max. sound pressure level: |
500 µB (128 dB SPL= 115 mV). |
| Microphone impedance: |
Low impedance of 200 ohms. |
| Frequency range: |
30 Hz -12.000 Hz (-6dB points). |
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| Analyzers available: |
Portable Electroglottograph EG90 (see
separate homepage).
Power is supplied from the PC. Max. 1 mA is used for the opto-coupler
which isolates the patient from the computer.
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| Amplifier: |
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| Operational amplifier: |
A dual operational amplifier
type LMC 662. |
| Amplification: |
First stage: 0 - 20 dB semi-adjustable for
calibration.
Second stage: 0, 10, 20, 30, 40, 50 dB |
| Dynamic ranges: |
25-80, 35-90,45-100,55-110, 65-120,75-130
dB. |
| Signal-to-noise ratio: |
PA14 Increases the S/N ratio of the Sound
Card with 12-15 dB. |
| Frequency range: |
30-12000 Hz (-3dB points). |
| Input sockets: |
(1) Microphone input via 3-pole Mini-Din
socket (left channel),
(2) Analyzer input via 4-pole Mini-Din socket (switchable between
right channel and left channel).
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| Max. microphone input level: |
115 mV corresponds to 128 dB SPL in the
microphone. |
| Max line input level: |
975 mV RMS. |
| Max. output level: |
Distortion starts at 1.2 volts RMS. |
| Power supply: |
0.76 mA is drawn from the SoundBlaster
+5 volt supply, 1.2 mA is drawn from buttons 6 and 7. |
| Output cables: |
Two cables, one for power (15
pin D-connector) and one for signal out (mini- stereo jack).
Both are supplied with the PA14 amplifier. |
| Size: |
120 x 64 x 39 mm. |
| CE marking: |
PA14 are certified according
to the directive EN 60950 "Safety of information technology
equipment. |
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