IEC 60118-15-2012 pdf free.Electroacoustics – Hearing aids – Part 15: Methods for characterising signal processing in hearing alds with a speech-like signal.
The procedure uses a speech-like test signal and the hearing aid settings are set to those programmed for an individual end-user or those recommended by the manufacturer for a typical end-user for a range of flat, moderately sloping or steep sloping audiograms, so that the measured characteristics are comparable to those which may be obtained by a wearer at typical user settings.
The purpose of this standard is to ensure that the same measurements made on a hearing aid following the procedures described, and using equipment complying with these requirements, give substantially the same results.
Measurements of the characteristics of signal processing in hearing aids which apply nonlinear processing techniques are valid only for the test signal used. Measurements which require a different test signal or test conditions are outside the scope of this standard.
Conformance to the specifications in this standard is demonstrated only when the result of a measurement, extended by the actual expanded uncertainty of measurement of the testing laboratory, lies fully within the tolerances specified in this standard as given by the values given in 6.1.
Measurement methods that take into account the acoustic coupling of a hearing aid to the individual ear and the acoustic influence of the individual anatomical variations of an end-user on the acoustical performance of the hearing aid, known as real-ear measurements, are outside the scope of this particular standard.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60118-7, Electroacoustics — Hearing aids — Part 7: Measurement of the performance characteristics of hearing aids for production, supply and delivery quality assurance purposes
IEC 60118-8:2005, Electroacoustics — Hearing aids — Part 8: Methods of measurement of performance characteristics of hearing aids under simulated in situ working conditions
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply:
3.1 sound pressure level
all sound pressure levels specified are measured in decibels (dB) referenced to 20 pPa
3.2 percentile sound pressure level
sound pressure level, in dB, below which a certain percentage of the measured sound pressure levels fall, measured in a 125 ms time interval, over a stated measurement period
Note I to entry: As an example: The 30th percenhile Sound pressure level is the sound pressure level below which 30 % of the measured sound pressure levels are found, and the remaining 70 % of the measured Sound pressure levels are higher.
Note 2 to entry: The 99th percentile may be interpreted as a peak sound pressure level indicator.
Note 3 to entry: The definition of percentile used here is according to general statistics. This definition may differ from other sciences such as acoustics.
3.3 International speech test signal ISTS speech-like test signal as defined in this standard
3.4 long term average speech spectrum LTASS sound pressure level measured in onethird-octave bands averaged over a long time period of speech
Note 1 to entry: For this standard a time period of 45 s is chosen.
3.5 occluded ear simulator OES ear simulator as defined in lEG 60318-4
3.6 estimated insertion gain of a hearing aid EIG estimate of the real-ear insertion gain as may be obtained across a group of persons
4 Limitations
This standard provides a technical characterisation of hearing aids and is not defining a clinical procedure for insertion gain measurements. However, results are shown as estimated insertion gain in order to improve the understanding of the results in relation to in situ conditions.
The estimated insertion gain may differ substantially from in situ results obtained on an individual person, due to differences between in situ conditions and the use of ear simulator or coupler as well as anatomical variation of head, torso, pinna, ear canal, and eardrum. Care should be taken when interpreting the results.
5 Setup
5.1 System overview
The goal of the test method is to provide an estimate of the insertion gain as may be obtained across a group of persons. For the purpose of characterizing a hearing aid for production, supply and delivery also the coupler gain on a 2 cm3 coupler as defined in IEC 60318-5 is provided.
This standard employs the international speech test signal (ISTS) for the measurement of hearing aid gain in one-third-octave bands and introduces the concept of gain for the long term average speech spectrum (LTASS gain) and the concept of time-aligned gain for a given percentile of the distribution of one-third-octave band sound pressure level of the ISTS (percentile gain) in 125 ms sections. Within each band, the LTASS gain is the gain averaged over the test duration. Within each band, the percentile gain for a given percentile is determined for each 125 ms section in the ISTS distribution which has the sound pressure level of the given percentile, and these gains are averaged over the duration of the test.
The methods of this standard yield an estimated insertion gain (EIG) (preferred) and a 2 cm3 coupler gain (optional) for the LTASS and the 30th, 65th and 99H percentiles of the ISTS.
For the EIG measurement, the ISTS is spectrally shaped by the tree-field to the hearing-aid- microphone transformation for the type of hearing aid being tested. The output of the hearing aid is preferably measured in an occluded ear simulator but may also be estimated from 2 cm3 coupler sound pressure level by adding the occluded ear simulator to 2 cm3 coupler difference. The EIG (calculated as the LTASS gain or as the speech gain at various percentile sound pressure levels) is derived by subtracting the relevant ISTS band level and the manikin unoccluded ear gain (IEC 60118-8:2005, Annex B) from the hearing aid output band level.
For the 2 cm3 coupler gain measurements, the input to the hearing aid is the ISTS and its output is the 2 cm3 coupler Sound pressure level.IEC 60118-15 pdf free download.