Overview
IEC 60118-15:2012 is an international standard developed by the International Electrotechnical Commission (IEC) for the characterization of signal processing in air-conduction hearing aids using a speech-like test signal. This standard introduces and specifies the International Speech Test Signal (ISTS), a signal designed to closely represent characteristics of real speech. The procedures outlined in IEC 60118-15 enable consistent, reproducible measurements of hearing aid performance across different devices and testing facilities, supporting reliable product assessment for production, supply, and delivery.
The standard is especially relevant for manufacturers, audiologists, and laboratories engaged in hearing aid development and quality assurance, aiming to ensure uniform measurement results by relying on methods that use speech-like signals and equipment conforming to international requirements.
Key Topics
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International Speech Test Signal (ISTS): The standard establishes ISTS as the preferred test signal, which mimics the spectral and dynamic features of normal speech. ISTS is composed of recordings from female speakers in multiple languages, providing a reliable reference for realistic speech testing.
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Estimated Insertion Gain (EIG): Procedures for deriving EIG using ISTS, measured through either an occluded ear simulator or a standardized coupler, allow estimation of the average real-ear gain provided by a hearing aid.
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Coupler Gain Measurement: The standard details how to determine coupler gain using a 2 cm³ coupler (in line with IEC 60318-5), which is commonly used in hearing aid manufacturing and supply chains.
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Measurement Consistency: By standardizing the test environment-including equipment, calibration requirements, and input levels-IEC 60118-15 ensures that results are highly repeatable, regardless of where the tests are conducted.
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Test Signal Bandwidth and Levels: The ISTS used in these procedures covers a wide frequency range (250 Hz to 6,300 Hz for key measurements), and is calibrated to a long-term average speech level of 65 dB SPL to simulate typical conversational speech.
Applications
IEC 60118-15:2012 is applicable for:
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Hearing Aid Manufacturers: Ensures consistent performance characterization during development and quality assurance. Helps verify that products meet international expectations for signal processing behavior using a speech-representative test.
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Independent Test Laboratories: Provides procedures and requirements to conduct standardized performance tests across various hearing aid models for reliable inter-laboratory comparison.
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Procurement & Delivery: Supports transparent specification and supply processes, allowing buyers to compare hearing aids based on standardized EIG and coupler gain measurements.
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Research & Product Development: Facilitates data-driven improvements in hearing aid algorithms and acoustic design by enabling precise signal processing assessments using the ISTS.
It is important to note that this standard focuses on laboratory-based technical measurements and does not address real-ear measurements that account for individual anatomical variations.
Related Standards
For comprehensive hearing aid testing and performance evaluation, IEC 60118-15:2012 is used in conjunction with several related international standards:
- IEC 60118-7: Measurement of performance characteristics of hearing aids for production, supply, and delivery quality assurance purposes.
- IEC 60318-4 & IEC 60318-5: Define the requirements for occluded ear simulators and 2 cm³ couplers used in hearing aid and earphone testing.
- IEC 61260: Specifies performance requirements for octave-band and fraction-octave-band filters, essential for the analysis of frequency response in ISTS measurements.
- IEC 60118-8: Addresses methods of measurement of performance characteristics of hearing aids under simulated in situ working conditions.
By adhering to IEC 60118-15:2012 and its related standards, stakeholders in the hearing aid industry can achieve robust, standardized assessment of electroacoustic performance, fostering confidence and comparability in hearing aid technologies worldwide.
Open preview (PDF)Electroacoustics - Hearing aids - Part 15: Methods for characterising signal processing in hearing aids with a speech-like signal
