The IntegraTEST HearMaster 3.0 Test System is a complete solution for production testing and characterization of hearing aid devices and loadspeakers. It combines a flexible measurement system with the capability of high throughput which makes it the ideal solution for all types of testing. The test system is VXI based, using a high performance PC as Slot 0 controller, hosting many of the measurement functions, and controlled from a standard PC running a LabVIEW® application. The application program is a stand-alone program that does not require any knowledge of LabVIEW to use, but can be programmed only by means of filling out standard menus. In this way complicated test programs can be implemented fast and efficiently without being an expert programmer, still it is possible for the experienced user to extend the program by adding test modules written in LabVIEW or if necessary in C. The test system provides a unique architecture to improve performance. In contrary to the way normal LabVIEW program generate instrument commands, the HearMaster test system has the option to pre-generate the commands, this significantly speed up execution time for production testing where the same tests are repeated over and over again.

The system features advanced signal generating capabilities of an audio generator combined with measurement /analysis capabilities of a digital signal processing based audio analyzer. A number of highly efficient DSP processing features is available for mixed signal test. Using industry standard concepts such as VXIbus instrumentation, LabVIEW, SCPI commands, MS-Windows provides an open, user friendly approach which improves return on investment and easy upgrading of a given system

Modes

Frequency Sweep

This mode is used for fast and comprehensive measurement of a given steady state, pure-tone response. Built-in adaptive filtering and use of statistical methods provide a selective measurement of each excitation frequency, offering user defined accuracy without sacrificing throughput.

Flexible settings of sweep frequency and amplitude features an optimized overall measurement time to reduce throughput. This obtained by differentiating the frequency density over the frequency range, for instance providing high density for resonance peak only.

Distortion measurement such as: Harmonic, intermodulation, and Difference Frequency Distortion are facilitated.

Amplitude Sweep

The purpose of the Amplitude Sweep is to measure the steady-state input/output relationship for an excitation signal having fixed frequency and variable (stepped) amplitude.

Two types of distortion measurement are available in this mode: Harmonic and intermodulation.

Multi-tone

In this mode, the multi-tone excitation signal is used to optimize the execution speed of the steady state frequency response measurement. The multi-tone stimuli can be programmed to comprise a sequence of multi-tone signals, each such multi-tone signal containing a sequence of multi-tones. A given signal of multi-tones may contain an arbitrary number of tones, including the start and stop frequency, as well as the frequency step type (linear or logarithmic). Programming of user defined, arbitrarily distributed frequencies, is supported.

High speed and high signal-to-noise ratio can be obtained simultaneously, by dividing the multi-tone into separate excitation signals. The separate responses are subsequently combined to obtain the final frequency response curve. The phase of each tone in a given signal is randomly selected, thereby lowering the crest-factor of the signal and preventing phase shift in the signal path to cause unexpected overloads.

The multi-tone signal can be highly complex and must be created carefully. The following issues must be taken into account:

1. The crest factor of the signal is important. The crest-factor is the relation between the peak value and the RMS value of the time signal.
2. The amplitude of each tone in relation to the final signal. If many tones are used in the multi-tone signal then each of the tones must have a smaller amplitude, which means a poorer signal to noise ratio.

Because of the need to measure performance at different frequencies, conventional testing uses a stepped frequency signal to measure frequency response, distortion and noise at many frequency points. However a different class of test signals well suited for this application is the multi-tone signal. Because all data points for all measurements are acquired simultaneously, the test speed is increased dramatically. Other benefits are that the multi-tone signal is a more realistic stimuli than the pure sine wave.

Programming of user defined, arbitrarily distributed frequencies is supported. High speed and high signal-to-noise ratio can be obtained simultaneously, by dividing the multi-tone into separate excitation signals. The separate responses are subsequently combined to obtain the final frequency response curve. The multi-tone stimuli can be programmed to comprise a sequence of multi-tone signals, each such multi-tone signal containing a sequence of multi-tones. A given signal of multi-tones may contain an arbitrary number of tones, including the start and stop frequency, as well as the frequency step type (linear or logarithmic). The phase of each tone in a given signal is randomly selected, thereby lowering the crest-factor of the signal and thus preventing phase shift in the signal path to cause unexpected overloads.

The creation of a multi-tone signal can be rather time consuming and depends on the complexity of the defined signal. To improve the speed the system includes a cash function that stores up to 10 generated signals. A control called index is used for specifying where to store the signal. The function works automatically so before generating the signal it checks if the signal already exist in the cash. Therefore it can also be noticed that the first time the test is performed, it can take several seconds before the actually measurement starts, this is the time used for calculating the signal. The following executions then runs at full speed.

The multi-tone signal can be calibrated to the stored calibration curve. This is selected under the Output group of parameters.

To minimize the effect of intermodulation distortion and other unwanted results, the multi-tone test mode has the feature of automatically dividing the signal into separate signals that later will be combined into a single results. This means that it is hidden for the user that the measurement actually is a result of several separate measurements. This is controlled by the Signals control on the front panel, where it is defined how many groups the signal should be split into. Setting Signals to one is the same as disable this feature. How the signal actually is split is controlled by the Audio Subsystem and optimized with some advanced algorithms.

Impulse Response

This mode is used to estimate a systems impulse response by measurement of both the input signal and the output signal. Three excitation signals are available: Impulse, MLS, and Multi-tone.

Nth Octave Analysis

In this mode the instrument can used to measure the internal noise generated in the hearing aid, as recommended in the IEC std. 118-0 (1983). The instrument uses FFT-techniques to synthesize an A-weighted third-octave noise spectrum. The number of octave bands is programmable and only limited by the upper measurement bandwidth. It is possible to bypass the A-weighting of the signal. By using the flexible post-processing facilities the Equivalent Input Noise Spectrum can easily be obtained by subtracting a predetermined pure-tone–gain response from the measured third-octave spectrum.

AGC-dynamic

This mode is designed especially for testing Hearing aids with automatic gain controls circuits according to IEC Standard 118-2. The purpose is to determine the dynamic input/output characteristic. This is carried out in three steps. First, the response to a sine wave modulated by a square pulse is measured. Then the envelope to the response is calculated by applying a RMS detector, which converts each sample points in the response to a RMS value. Finally, attack and release time (or recovery time) is detected by using the following technique: A reference level is calculated as the mean value for the 10 rightmost points in the attack or release RMS response. The attack or release time is then found at the first sample point - searching from right to left, which deviate more than a specified number of dB from the reference level.

AGC-steady

This mode is used to measure the steady-state behavior of hearing aids with automatic gain controls, as recommended in IEC std. 118-2 (1983). The instrument uses a single tone with programmable frequency and amplitude sweep as excitation. Bandpass filtering and statistical methods are used to ensure high accuracy and steady-state conditions. The measurement result are: Steady-state input/output characteristic (AGC-curve) and AGC-limit (alternatively known as AGC-threshold).

Specification for this mode is the same as for the Amplitude Sweep mode.

Level

In Level mode, the instrument continuously measures the output response for one or more input excitation signals, each with programmable frequency and amplitude. Bandpass filtering of the separate tones is used to ensure high accuracy by excluding the distortion products. This mode can be used to adjust (or test) the gain control position.

Specification for this mode is the same as for the Multi-tone.

Spectrum Analyzer

This versatile mode is intended to be used as an oscilloscope for monitoring a captured signal in time and/or frequency domain. A single tone generator with programmable amplitude and frequency is available as excitation signal. The delay from start of signal generation to signal capture is also programmable, and so is the sampling frequency and the number of samples to be captured.

The following measurement results are available: Time signal, RMS Spectrum, Nth Octave Spectrum, THD, SNR, Total RMS, Distortion, Noise

Battery Supply Current

Example on setting up the current measurement.

Post Processing

A wide range of general-purpose post-processing facilities is available in the Audio Analyzer. When a measurement is completed, the result is passed from the Audio Analyzer to the Vector subsystem where it can be stored for later use, or scalar measurement result can be derived from the primary result vector. The Vector subsystem sends measurement data to the Calculate subsystem, which facilitates a smoothing subsystem, an advanced limiter subsystem, and a transformation subsystem (spectrum or histogram).

HI-PRO

The system has full support for programming the HI-PRO box.