Showing papers by "AG Armin Kohlrausch published in 1994"

Effect of masker level on overshoot in running‐ and frozen‐noise maskers

Abstract: Masked thresholds were measured with running‐ and frozen‐noise maskers. The 5‐kHz signal was 2 ms in duration. The masker was low‐pass noise (20 Hz–10 kHz); its total duration was 300 ms. The overall level of the masker was 30, 50, or 70 dB SPL. The onset of the signal was delayed by 0, 3, 8, 18, 198, or 278 ms relative to the onset of the masker. In all frozen‐noise measurements, the signal was added to the same fine structure of the noise. Overshoot in frozen noise was measured for two starting phases of the signal that led to a 10‐dB difference for large signal‐onset delays. In all three configurations (running noise and frozen noise with two different signal phases) masker level had a similar influence on overshoot. At the intermediate masker level (50 dB SPL), a significant amount of overshoot (up to 15 dB) was observed in all three conditions. At the low and the high masker levels, overshoot was very much reduced, and even became negative in most conditions for the 30‐dB‐SPL masker. For the 50‐dB frozen‐noise masker, the total variation of thresholds with signal phase was 8 to 11 dB for long signal‐onset delays, but only 3 to 6 dB for short delays. For the low‐ and high‐level maskers, where only a small overshoot was observed, the threshold variation with phase for a signal at masker onset was the same as that for the long‐delay condition. An explanation for the variation of signal detectability with masker level is proposed that refers explicitly to the compressive input–output characteristic of the basilar membrane at intermediate levels.

Bit-Rate Saving in Multichannel Sound: Using a Band-Limited Channel to Transmit the Center Signal

Abstract: A method is proposed to achieve full-frequency-range three-channel (left, right, and center) sound reproduction in systems that have only two full-range sound channels and some band-limited commentary channels. The low-frequency part of the center signal, which matches the bandwidth of the commentary channels, is added to the (multilingual) speech signals in each of the commentary channels. The remaining high-frequency part is added in the left and right channels as in conventional mixdowns. Sound reproduction of this signal by a conventional two-channel receiver remains unaltered. The low-frequency part of the center signal is mixed to the left and right signals together with the speech once the user has selected a commentary channel. Three-channel reproduction is obtained by routing the selected commentary channel to a central loudspeaker. Listening tests revealed that sound reproduction according to the proposed scheme could not be distinguished from original three-channel reproduction. This scheme can be applied to proposed standards such as D2MAC and MPEG2.