HP RM500SL manual Loud Vocal Effort Effect re nominal band SPL

digitized speech passages and the single-talker ICRA distorted speech are provided. Each has a duration of 10 – 15 seconds and may be presented as a single passage or in a continuous loop. In order to provide a repeatable speech signal to the device under test, the signal path must be equalized prior to the presentation of the speech signal. This is accomplished by presenting a 896 ms pink noise burst at the selected speech level, 256 ms prior to the start of each speech passage and adjusting a digital filter to provide a flat response at the reference microphone.

The two “Speech-std” signals are by the same male talker, filtered to provide the long-term average speech spectrum (LTASS) recommended by Cox & Moore (1988) for average vocal effort. This is the LTASS assumed in the Desired Sensation Level (DSL) method of hearing aid fitting. The “female” and “child” signals have been chosen to provide a range of spectra and are presented “as recorded” without any processing. Overall SPLs of 50, 55, 60, 65, 70 and 75 dB (at the reference microphone) are available. Soft and Average levels (50 - 70 dB SPL) have the same spectrum. A Loud vocal effort filter is applied to the 75 dB level signals. This is shown in Figure 2.

The ICRA distorted speech signal is a recording of an English-speaking talker that has been digitally modified to make the speech largely unintelligible. The resultant signal has many of the properties of real speech but has a harsh sound and lacks harmonic structure. The latter may be significant for hearing aids which use this property of speech to control noise reduction schemes. The LTASS is similar to the “Speech-std” signals up to 5 kHz.

The test systems provide a simulated real-ear mode (S-REM) in which measurements made in the 2 cc coupler in the test chamber are converted to estimated real ear SPL. In this mode, the effects of hearing aid microphone location need to be included in the test signals so spectra are further altered to include the microphone location effects shown in Figure 3.

LOUD VOCAL EFFORT EFFECT re nominal band SPL

	20.00
	15.00
SPL (dB re NOMINAL)	10.00
	5.00
BAND
	0.00
	-5.00
	200	250	315	400	500	630	800	1000	1250	1600	2000	2500	3150	4000	5000	6300	8000

BAND CENTER FREQUENCY (Hz)

Figure 2: Loud vocal effort effect in dB re nominal band levels. Nominal band levels are band levels for an overall SPL of 65 dB. This shaping is applied to the 75 dB SPL speech and ICRA signals.

In addition to these well-controlled and repeatable signals, live speech may be used as a test signal. It will, of course, be unequalized and at an uncontrolled level.

07/05/06	© Etymonic Design Incorporated, 41 Byron Ave., Dorchester, ON, Canada N0L 1G0	Page 3
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