3 - AS 60118.2-2007 Hearing aids Part 2: Hearing aids with automatic gain control circuits
4 - PREFACE
5 - CONTENTS
7 - 1 Scope
7 - 2 Object
8 - 3 Conditions
8 - 3.1 General conditions
8 - 4 Explanation of terms
8 - 4.1 Automatic gain control ( AGC)
8 - 4.2 Steady- state input/ output graph
8 - 4.3 Lower AGC limit or AGC threshold
8 - 4.4 Compression ratio ( between specified input sound pressure level values)
8 - 4.5 Dynamic output characteristics
8 - 4.6 Attack time
8 - 4.6.1 Attack time for the normal dynamic range of speech
9 - 4.6.2 High level attack time
9 - 4.7 Recovery time
9 - 4.7.1 Recovery time for the normal dynamic range of speech
9 - 4.7.2 High level recovery time
9 - 4.8 AGC activated frequency response
9 - 4.9 Operating frequency range of the AGC
9 - 4.10 Overall root- mean- square sound pressure level ( overall r. m. s. SPL)
9 - 4.11 One- third- octave band level
9 - 4.12 Auto- spectrum ( power spectrum)
9 - 4.13 Cross- spectrum ( GAB)
10 - 4.14 Coherence
10 - 4.15 Synchronous analysis
10 - 5 Steady- state input/ output graph
10 - 5.1
10 - 5.2 Methods of measurement
10 - 6 Dynamic output characteristics
10 - 6.1 Characteristics to be measured
11 - 6.2 Methods of measurement
11 - 6.2.1 Dynamic output characteristics for speech levels
11 - 6.2.2 Dynamic output characteristics for high level input
11 - 7 Non- linear distortion
11 - 7.1 Transients
11 - 7.2 Harmonic distortion
11 - 7.2.1 Characteristics to be specified
11 - 7.2.2 Methods of measurement
12 - 7.3 Intermodulation distortion
12 - 8 Effect on steady- state and dynamic performance with respect to variation in battery or supply voltage
12 - 9 AGC activated frequency response of hearing aids with a single channel
12 - 9.1 Introduction
12 - 9.2 General conditions
12 - 9.3 Test equipment
13 - 9.4 Test conditions
13 - 9.5 Measurement
13 - 9.5.1 Determination of the operating range of the AGC
13 - 9.5.2 Measurement of the AGC activated frequency response
14 - 9.6 Frequency response recording chart
14 - 10 Frequency response of hearing aids with AGC circuits in operation
14 - 10.1 General
15 - 10.2 Test enclosure
15 - 10.3 Test conditions
15 - 10.3.1 Noise input signal
16 - 10.4 Test equipment
17 - 10.5 Measurements of frequency responses
17 - 10.5.1 Comprehensive frequency responses and basic frequency response ( acoustic gain)
17 - 10.5.1.1 Cross- spectrum method
17 - 10.5.1.2 Auto- spectrum method
18 - 10.5.1.3 Swept filter method
18 - 10.6 Frequency response recording chart
19 - Annex A (informative) Examples of measuring systems
22 - Annex B (informative) Smoothed data presentation
23 - Annex C (informative) Bibliography