Electrical audio signal processing systems and devices – Including amplitude or volume control – Automatic
Patent
1988-10-27
1990-08-07
Isen, Forester W.
Electrical audio signal processing systems and devices
Including amplitude or volume control
Automatic
381119, H03G 300
Patent
active
049474405
ABSTRACT:
Shaping of automatic audio crossfade is accomplished by adding a shaping function to the theoretical logarithmic crossfade function to decrease the rate of gain change at the limit of audibility. The gain change at each sample time within a crossfade interval is computed as a logarithmic function of the fractional part of the crossfade interval completed and the gain differential between the sources. The shaping function may be in the form of a cosine function that can be accessed with a look-up table that is added to the fractional part of the crossfade interval so that the gain change is expressed by:
ti G.sub.delta =20*log{(k-s(k))*10.sup.(G.sbsp.1.sup.-G.sbsp.2.sup.)/10 }
where S(k) is the shaping function, k is the fractional part complete and G.sub.1 -G.sub.2 is the gain differential between sources. The gain change is added to the current gain for the particular audio source and applied to a variable gain element for that source. The outputs of the variable gain elements are summed to produce the resulting output audio mix.
REFERENCES:
patent: 3020343 (1962-02-01), Aldridge, Jr.
patent: 3647928 (1972-03-01), Turner
patent: 3868585 (1975-02-01), Richmond
patent: 4306114 (1981-12-01), Callahan
patent: 4706537 (1987-11-01), Oguri
Auto Cross-Fader, David Edwards, Electronics Australia, Jan. 1978, vol. 39, No. 10, pp 48-51.
Bateman Robert
Christensen Donald R.
Gray Francis I.
Isen Forester W.
The Grass Valley Group Inc.
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