lenswaard,28 and the recommendations embodied in AES11-199129 all quote similar values. Are these lower limits reasonable? How audible is jitter
25 T. Shelton, "Synchronization of Digital Audio,"
Proceedings of the ALS 7th International Conference: Audio
in Digital Times (Toronto, Ontario, Canada,
1989).
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when its level is at the quantization noisefloor? An attractive approach to answering these questions is to model the hearing process itself, ie, find out whether a given jitter error is below the masked threshold due to the jittered audio signal - a method adopted by Julian Dunn.30 Correspondingly, a simple hearing model was developed in order to assess the audibility of jitter in a band-limited interface. Our model assumes that the error due to jitter is inaudible if it is below the threshold of hearing ('minimally audible field) at all frequencies. This approach will yield pessimistic results as far as error audibility is concerned, since the additional masking effect of signal tones is not considered, although masking of low-frequency noise by high-frequency tones is minimal. Recent work by Bob Stuart31 suggests that the audibility of errors in isolation may well be of higher significance than has previously been thought. We define the threshold of hearing in the frequency domain by Passing a cubic spline through the threshold data of ISO22632 and scaling by the gain of a typical audio system under critical listening conditions such that "0dB" refers to a sound-pressure level of 112dB at 1m per speaker.33 The error signal is then integrated at each frequency bin across a bandwidth defined by the equivalent rectangular noise
30 J. Dunn, "Considerations for Interfacing Digital Audio
Equipment to the Standards AES3, AES5 and AES11,"
Proceedings of the AES 10th International Conference:
Images of Audio (London
1991).
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