The Importance of Early Sound for Recording and Reproduction-Is the Quality of Digital Sound Transmission Sufficient?
The direct sound package DSP which arrives at the microphone, consists of the direct sound itself and very early reflections from nearly reflecting areas. This applies for speech and music. Musical instruments show a decay of around 1, 8 dB/ms, when erected by an impulse or measured with Time Delay Spectrometry (TDS). In a control room this DSP should be audible and should not be disturbed by parasitical reflections which may occur at reflecting surfaces. In a listening test the question had to be answered which level of reflections could be allowed. A V-criteria was defined which follows the threshold of any change of perception. With a limit of approx. -27 dB a V-criteria gap of 15ms was found. As long as the reproduction of sound is poor due to monitoring speakers with an insufficient impulse response characteristic the DSP can not be fully reproduced. Instead a loudspeaker sound package LSP arrives., consisting of some delayed sound pressure fronts in the range of 0 to 1,5 ms. Well designed testloudspeakers or good headphones present the adequate response. The other question is whether the transmission line is good enough. The microphone can convert the signal to a maximal amplitude with 0,008 ms. These aspects of early sound will be discussed in the paper.
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