MED Associates ANL-940-1 User manual

instrumentation and software for research
ULTRASONIC MICROPHONE AND
AMPLIFIER
ANL-940-1
USER’S MANUAL
DOC-262
Rev. 1.2
Copyright ©2014
All Rights Reserved
Med Associates Inc.
P.O. Box 319
St. Albans, Vermont 05478
Phone: [phone]
Fax: [phone]
www.med-associates.com

ANL-940-1 Ultrasonic Microphone and Amplifier
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DOC-262 Rev 1.2 Copyright © 2014
MED Associates, Inc.
notes

ANL-940-1 Ultrasonic Microphone and Amplifier
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DOC-262 Rev 1.2 Copyright © 2014
MED Associates, Inc.
Table of Contents
Chapter 1 | Introduction ........................................................................................................1
Specifications................................................................................................................................... 1
Notes ............................................................................................................................................... 1
Requirements .................................................................................................................................. 1
Chapter 2 | Hardware ............................................................................................................2
Chapter 3 | Operation............................................................................................................3
Appendix A ............................................................................................................................6
Quantitative Analysis of Sound Pressure Levels .......................................................................... 6
Appendix B | Contact Information..........................................................................................9

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CHAPTER 1 | INTRODUCTION
The ANL-940-1 Ultrasonic Microphone and Amplifier accurately measures both the amplitude
and frequency of ultrasonic vocalizations emitted by laboratory rodents. This device is suitable
for measuring motivational behavior in drug addiction studies, mother-pup separation, isolation
stress, social interactions, sexual encounters, and many other paradigms. The instrument
produces an analog voltage output (BNC Connector) that is proportional to sound pressure level.
The analog output can be connected to third party data acquisition systems. (e.g. National
Instruments)
Spec ifications
The frequency response of the ANL-940-1 is linear (+/- 4 dB) up to 100 kHz.
The analog output is +\- 14 Volts.
The ANL-940-1 microphone and preamplifier combination are calibrated to provide 1 volt peak
output into a high impedance load when excited with a 50 kHz ultrasound sine wave with a peak
pressure level of 1 Pa, or Lp= +94 dB SPL (20 µPa = 0 dB). Peak levels were selected for ease of
setting up associated A-to-D converters, as the peak value could be easily related to the full-
scale count of the converter. This calibration is independent of distance from the sound source
and reflects the actual sound pressure at the face of the microphone.
The output impedance of the ANL-940-1 amplifier is 50 Ohms and must be considered when
connecting the unit to other measurement equipment.
Notes
1. The high impedance load assumed for calibration is high relative to 50 Ohms and the
loading effect of low impedances must be considered. For example, 500 Ohm load has
an error of less than 1 dB, while a 10000 Ohm load has an error of less than 0.05 dB.
2. If the A-to-D has 50 Ohm load, the sensitivity is reduced to 0.5 V peak due to the drop
across the ANL-940-1 internal impedance. Many instruments have a fixed 50 Ohm input
impedance, so the input impedance of your recording hardware should be determined if
your goal is to make quantitative measurements of vocalization amplitudes (in dB).
Requir ements
- Third party data collection hardware and software

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CHAPTER 2 | HARDWARE
The ANL-940-1 includes a Microphone and an Amplifier. A power supply is also included, which
provides a minimum of 12V, 500mA. The brand and type of power supply depends on the user’s
country.
The ANL-940-1 Ultrasonic Microphone (Figure 2.1) is designed for sound waves in the 500Hz to
100KHz range.
Figure 2.1 –ANL-940-1 Microphone with Exploded Views of Connector and Microphone
The amplifier on the ANL-940-1 is calibrated to provide a relatively flat frequency response for
the microphone (+/-4 dB from 500 Hz through 100KHz). It uses a 12V 500mA DC power and
outputs the signal to a BNC port.
Figure 2.2 –ANL-940-1 Microphone Amplifier

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CHAPTER 3 | OPERATION
Two output settings are available ‘DIRECT’ and ‘LPF’. LPF applies a low-pass filter to the output
signal with a cutoff frequency of 100 KHz for use as an anti-aliasing filter. The front panel has an
access for the calibration screw marked ‘CAL.’ This calibration screw adjusts the overall gain of
the amplifier. The ANL-940-1 has been pre-calibrated at the factory. Do not adjust the
instrument gain if you will be using the ANL-940-1 to quantify the actual amplitude (dB) of
rodent vocalization. Refer to Appendix A for more information regarding measurement of
sound pressure level amplitudes.
1. Place the microphone over the chamber
The microphone should be centered over desired location, and pointing at the subject of
interest. The picture in Figure 3.1 shows a typical setup for mouse open field ultrasonic
vocalization.
Figure 3.1 –Microphone Placed Over Cage (Microphone Support Not Included)

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2. Attach microphone to amplifier
The microphone jack is ‘keyed’ and only fits one way. Rotate until it slides in. Screw the outer
sleeve to the jack to prevent accidental disconnection.
Figure 3.2 –Microphone Connected to Amplifier
3. Connect amplifier to Data Acquisition Device (DAQ) using BNC cable
Med Associates, Inc. recommends using a National Instruments DAQ device, such as the myDAQ
or ELVIS. The ANL-940-1 has been tested with this equipment. For connection from the ANL-
940-1 BNC connector to the National Instruments DAQ device, the center and ground can be
screwed into the terminals. Alternately, Med Associates makes an ANL-940-DA-1 BNC adapter
for the myDAQ to interface with a National Instruments myDAQ device.
Figure 3.3 –Connect National Instruments myDAQ (shown with BNC Adapter) to ANL -940-1

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4. Plug in power supply and turn on amplifier
The power supply has a 2.1mm connector and supplies 12V, 500mA. Insert the connector into
the port on the back of the Amplifier and flip on the power switch.
Figure 3.4 - Back View of ANL-940-1 Microphone Amplifier
5. Select “LPF” or “Direct”
“Direct” passes the microphone input directly to the DAQ. “LPF” applies a low-pass filter to the
signal. The LPF is an anti-aliasing filter that attenuates signals above 100KHz. The “LPF” setting
is recommended.
Figure 3.5 –Location of Direct/LPF Switch
Direct/LPF
Switch
Insert power supply
connector to Power
Input port

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APPENDIX A
Quantitative Analysis of Sound Pressure Levels
Unlike many instruments on the market, the ANL-940-1 Ultrasonic Microphone and Amplifier is
a specialized device that is calibrated to produce a defined signal amplitude in response to a
standard sound pressure level. Thus, it is useful not only for recording the frequency profile of
rodent vocalizations, but also it can provide an accurate measure of the amplitude, or Sound
Pressure Level, of the vocalizations. For researchers interested in quantifying the amplitude of
vocalizations, special consideration should be given to the calibration specifications of the ANL-
940-1 instrument, as well as the physical layout of the recording environment, particularly the
distance between the microphone and the test subject.
To report standard Sound Pressure Levels (Lp), the level should be reported at a distance of 1
meter between the microphone and test subject. However, it is often inconvenient to configure
an arrangement in the lab where the microphone is at a distance of 1 meter from the test
subject. Thus, it is necessary to convert measurements obtained a distance of less than one
meter to the equivalent measure that would be obtained at a distance of 1 meter.
Calculating the 1 meter equivalent sound pressure level depends on the expression of the initial
measurement. If the microphone output is recorded as a voltage, the voltage expected at a
distance of one-meter is obtained by multiplying the measured voltage by the measurement
distance in meters.
Example: If a microphone placed 0.25 m (or 1/4 m) from the source produces a sound
pressure level of 30 mV (0.03V), the equivalent pressure at 1 m would be 30 mV * 0.25 = 7.5
mV ( or 30mV / 4). Recall that the ANL-940-1 has a calibration scaling of 1 Pa/V. Thus, the
equivalent sound pressure level at 1 m would be 0.0075 V * 1 Pa/V = 0.0075 Pa.
Considering the large variation of sound pressure levels typically encountered and the need to
multiply or divide to obtain sound pressure in Pa at one-meter, it is usually easier to calculate
sound pressure using logarithms. A standard system has been developed (ANSI S1.1-1994)1to
yield a logarithmic measure of the effective sound pressure level of one sound relative to a
reference value. Thus, effective sound pressure levels are measured in decibels (dB) above a
standard reference value.
Sound Pressure Level (SPL), or sound level (Lp), is defined in ANSI S1.1-1994 as1
Where pref is a sound pressure level reference value, and prms is the root mean squared (rms)
value of the sound pressure level for the measured signal.

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NOTE: Sound Pressure Level is often abbreviated simply as SPL. Sometimes variants of the
actual measurement unit are used, such as dB (SPL), dBSPL, or dBSPL. These variants are not
recognized as units in the ANSI standard. The unit dB (SPL) is sometimes abbreviated to just
"dB", which can give the erroneous impression that a dB is an absolute unit by itself. Keep in
mind that SPL measures (Lp) are not absolute measures in and of themselves. They are
expressing one sound pressure relative to a reference sound pressure.
The commonly used reference sound pressure level (pref) in air is 20 µPa (rms), which is usually
considered the threshold of human hearing (roughly the sound of a mosquito flying 3 m away)1.
Most sound pressure level measurements will be made relative to this level, meaning 1 Pa will
equal a SPL of 94 dB (20 log(1 Pa/0.00002 Pa) = 94 dB).
If a sound pressure p1, is measured at a distance r1, one can calculate the sound pressure p2at
another position r2using the following equation:
Converting the resulting pressure to Sound Pressure Level (in dB) allows the correction for
distance to be accomplished by simply adding logarithms.
20 log(p2) = 20 log(p1*r1/r2) = 20 log(p1) + 20 log(r1) - 20 log(r2)
In the case where r2= 1 meter,
Lp@1 meter = Lp@r1+ 20 log(r1)
Figure A.1 - Graph of 20 log(r1) for distances less than 1 meter

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Figure A.1 shows a plot illustrating the correction factor (in dB) that should be subtracted from
SPL measurements taken at distances less than 1 meter to scale them to the equivalent SPL that
would be obtained at 1 meter. Some commonly used measurement distances are indicated. To
obtain the correction factor for any distance less than one meter, simply take the logarithm of
the distance and multiply by 20. Subtract this value from the SPL you measured and this will
give you the equivalent SPL at 1 meter. It is convention to express SPL measurements at a
distance of 1 meter. However, always be sure to state the distance used in your measurements
when publishing papers. This will aid other readers in interpreting your data, and represents
good scientific practice.
Example: Setting up to make measurements that reflect expected pressure levels at one-meter.
1. Determine the distance from the sound source to the microphone, e.g., 0.25 meters.
2. If possible, set the A-to-D converter gain such that the largest expected analog signal
provides a digital output slightly smaller than the maximum converter output count.
3. If possible, adjust the scaling factor of the display software such that the peak value of a
1 volt 50 kHz sine-wave input produces a reading of
94 dB + 20 log(distance)
which for a distance of 0.25 m yields
94 dB + 20 log(0.25 m) = 94 dB –12 dB = 82 dB
The above scaling may be accomplished by either using the known gain factor for the A-to-D
converter and the display software, or by applying a 1 volt peak (0.707 V rms) 50 kHz signal to
the converter input using a signal generator. The test generator output level may be
determined either by direct measurement, or, if the generator provides a calibrated output, by
using the set value directly. If it is not possible to scale your A-to-D recording hardware and
software, you will need to do post hoc scaling of your recording signals using some other data
processing method (e.g. export data from your recording system to an Excel spreadsheet).
NOTE: if the signal generator output is set using the generator's output level control, be sure to
load the generator output with the proper load. For example, if the generator output
impedance is 50 Ohms, the output must be loaded with 50 Ohms. In the case where the A-to-D
being used has a high input impedance, the stated generator output voltage must be doubled
(i.e., a setting of 0.5 V peak will produce a 1 V peak signal into a high impedance load). Finally, if
a test signal of 1 V peak causes the output of the A-to-D to saturate, reduce the amplitude of the
test signal by a factor of ten to 0.1 V peak and replace the factor of +94 dB with +74 to
compensate for the reduced signal level.

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A note on rms values
Expressing signal levels in rms equivalent values assumes an averaging over either time or space,
and is usually used to express the spread of a measurement. The rms value of a single
measurement is the measured value. In the case of a pure sine-wave, the measurement is
assumed to be averaged over a full cycle and is typically used to calculate the power of the
signal. For example, a sine-wave with an amplitude of 1 V peak measured across a 1 Ohm
resistor will cause 0.707 Watts to be dissipated in the resistor, as the rms voltage of a 1 V peak
sine-wave is 0.707 V. For more complex signals, such as a rodent vocalization, the rms value
must be computed by averaging the square of the vocalization over a selected duration, and
then taking the square-root of the result, if indeed the energy put into the vocalization is of
interest.
References:
1http://en.wikipedia.org/wiki/Sound_pressure#Sound_pressure_level
APPENDIX B | CONTACT INFORMATION
Please contact MED Associates, Inc. for information regarding any of our products.
Visit our website at www.med-associates.com for contact information.
For technical questions, email [email protected].