This sequence follows the test standard detailed in EN50332-1 (2013) for measuring the maximum sound pressure for portable music players and the earphones/headphones they are bundled with. The test involves loading a weighted pink noise stimulus file (as specified by IEC 268) onto the portable device and playing it through the earphones at the player’s maximum volume.
This sequence performs two of the measurements from the ANSI hearing aid test standard S3.22-1996. The first part, in accordance with section 6.7 of the standard, helps the user set the reference test gain for the hearing aid, which is used for multiple measurements in the standard. The second part, from section 6.12, tests the equivalent input noise (EIN) of the device.
The Hearing Aid Standard suite of sequences contains all the major tests from ANSI S3.22 and IEC 60318-7, as well as some of the additional ‘Annex C’ sequences from the 2003 ANSI standard. Each test, as outlined in the standards, is contained in a single test sequence. These sequences can each be run independently. There are also several full test sequences, which call up the required individual tests to run a complete standard test suite.
These two test sequences are designed to test the hearing aid compatibility of a telephone according to the TIA 1083 and FCC Part 68.316 standards. These sequences, which rely on the user having radial and axial HAC probes, play the appropriate test signals, measure the response and compare them to the limits in the standard. These pre-written sequences enable the user to immediately test to the relevant standards, and can be fully modified to meet any custom testing needs if desired.
This test sequence implements all the electroacoustic tests required by TIA-470.110-C, outputting the results as a report or writing to a database. Future releases of this sequence are planned to cover headset and speakerphone testing, and will be developed when the relevant subsections of TIA-470 are approved. The test sequence contains all the major clauses of TIA470C, and also includes calibration sequences and sub-sequences. The test sequences can be used as they are to test to the standard, or modified by the user for custom in-house tests based on the standard.
The first measures the frequency and sensitivity and displays two graphs: absolute level in dBFS, and the same response curve but normalized to 0 dB at 1 kHz.
The second sequence uses the substitution method to test a digital MEMS microphone frequency response with a source speaker that is not or cannot be equalized. The MEMS microphone is simultaneously measuring with a reference microphone , and by subtracting the response of the reference microphone from the DUT microphone the response and sensitivity of the device under test is revealed.
Measuring Digital Microphone PSR (Power Supply Rejection)
The third sequence demonstrates a method for measuring a digital MEMS microphone’s power supply rejection performance (PSR). This sequence measures PSR at 217 Hz (the 217 Hz GSM TDM pulse often of concern) but is easy to modify to test at any frequency. A DC supply with a calibrated AC signal, simulating electrical interference is applied to the MEMS microphone. SoundCheck then records the audio from the DUT, analyzes it with a spectrum analyzer and extracts the RMS energy at the specific frequency of the simulated electrical interference and returns the PSR value. The setting of frequency, waveform type and amplitude of the simulated electrical interference is controlled entirely from within SoundCheck.
This sequence measures the directional response of a microphone and graphs the result as a polar plot. A log sweep stimulus is played from 100 Hz to 10 kHz at each angular increment, and the acquired waveform is analyzed using the Time Selective Response algorithm. This method allows the test to be performed in a non-anechoic environment by placing a window around the direct signal, eliminating the influence of reflections. Commands are sent automatically to the LT360 turntable via an RS-232 connection, instructing it to move in 10 degree increments after each measurement. The sequence measures the response every 10 degrees from 0 to 180 and mirrors the polar image, simulating a full 360 degree test while saving time. The response at each angular increment is compared against the on-axis response to create a normalized curve. This removes the influence of the device’s frequency response and sensitivity, such that the polar plot only shows the directional response. The final display also contains a graph of the directivity index in decibels versus frequency.
This sequence measures the self noise of a condenser microphone, using a spectrum analysis step and a power sum calculation to derive an RMS rating for the unit under test.
The sequence has several parts (some optional). The sequence intitally determines whether or not you have a high enough signal (signal being your microphone’s self noise) to noise ratio to accurately measure your microphone. It then takes a measurement from your microphone, creates a spectrum, accounts for the preamp gain, applies an A-weighting, and finally calculates the power sum. You are then prompted to enter the sensitivity of the microphone if it is known. The resulting display provides you with the equivalent input noise of your preamp, the self noise of your microphone in dBV, and also a result in dB(A) after factoring in the microphone’s sensitivity. You’re also provided with the waveform, a maximum voltage level, and the crest factor to check for sharp transients.
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