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(see AUDIO FILES for information on the *.wav files)
Ripple Noise and Iterated Rippled Noise (IRN) are generated as described in Figure 1. A sound source (usually a broadband noise) is delayed and added back to itself. The delayed noise may also be attenuated before being added back. As such the network shown at the top of Figure 1 is a description of a sound and its delayed and attenuated echo being added together as they would in the real world. The network may be cascaded or iterated in the two ways shown in Figure 1. In one case (ADD-ORIGINAL circuit), IRN is referred to as IRNO(d,g,n), where the O refers to original because the delayed noise is added back to the original noise, d is the delay in ms, g is between -1 and 1, and n is the number of stages of iteration (n=2 in Figure 1). In the other case (ADD-SAME circuit), IRN is referred to as IRNS(d,g,n), where S stands for same because the delayed noise is added back to the same added noise that occurred after the previous addition. This set of audio demonstrations indicates the effect of d (delay), g (gain or its inverse attenuation), n (number of stages of iteration), and the two types of networks (ADD-ORIGINAL and ADD-SAME) have on the perceived quality of a broadband noise source. Change in Delay (d). IRNO(d,1,4) stimulus is generated with d changing from 1, 2, 3, 4, 5, 8, 10, 16 ms.
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You should hear the pitch of the noise decrease from a pitch near 500 Hz to one near 100 Hz. In fact, in this case the perceived pitch is equal to the reciprocal of the delay.
Change in Number of Iterations (n). IRNO(4,1,n) stimulus is generated with n changing from 1, 2, 4, 6, 8, 16, 32, 64, 128 iterations.
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You should hear the strength or saliency of the pitch quality increase and that of the noisy quality decrease as the number of iterations increases. Change in the Gain (n). IRNO(4,g,6) stimulus is generated with g changing from 0.10, 0.25, 0.50, 0.75, 0.80, 0.75, 0.90, 0.95, 1.0.
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You should hear the strength or saliency of the pitch quality increase and that of the noisy quality decrease as g increases toward one.
Change between Positive
and Negative Gain, g=1 and g=-1. IRNO(4,1.0,3) vs.
IRNO(4,-1.0,3). When g=-1 it is the same as subtracting the
delayed noise rather than adding the delayed noise to the
undelayed noise. The first part of the stimulus is produced with
g=1.0 and the second part with g=-1.0. You should hear a pitch
change and perhaps a sight change in pitch saliency.
Change between IRNO
and IRNS. IRNO(4,1,3) vs. IRNS(4,1,3). The first part of the
stimulus is produced with the ADD-ORIGINAL circuit and the second
part with the ADD-SAME circuit. You will probably not hear any
change at all. This comparison is discussed in more detail in the
other ripple noise section (Why Iterated
Rippled Noise may be Temporally Processed). This section will
also describe some of the spectral and temporal properties of IRN
stimuli.
Suggested References:
Yost, William A., Hill, Richard, and Perez-Falcon, Tony, Pitch and Pitch Discrimination of Broadband Signals with Rippled Power Spectra, Journal of the Acoustical Society of America, 63, 1166-1173, 1978
Yost, William A., Patterson, R.D., and Sheft, S. A Time Domain Description for the Pitch Strength of Iterated Ripple Noise, Journal of the Acoustical Society of America 99, 1066-1078, 1996
Yost, William A., The Pitch of Iterated Rippled Noise, Journal of the Acoustical Society of America, Journal of the Acoustical Society of America 100, 511-518, 1996