Mixing, coding and decoding devices and methods

DETAILED DESCRIPTION It is therefore a primary object of the present invention to provide a mixing device and a mixing method which are capable of mixing bitstream data without having to convert the data into analog representation, as well as coding and decoding devices and methods employing such a mixing device or method.
It is a second object of the present invention to provide an audio signal interface device which is simple in construction and yet permits appropriate input of analog audio signals of plural channels.
It is a third object of the present invention to provide a mixing device which can perform high-quality mixing at low cost with minimized influence of noises and signal deterioration, as well as an audio system employing such a mixing device.
In order to accomplish the above-mentioned objects, the present invention provides a mixing device for mixing plural bitstream data, which comprises: a weighting circuit that weights a plurality of bitstream data for conversion thereof into respective plural-bit digital data; an adder circuit that adds together the respective plural-bit digital data outputted from the weighting circuit, so as to output added digital data; and a converter circuit that converts the added digital data into bitstream data.
The "bitstream data" is pulse-density-modulated (PDM) data and has a logical value "1" or "0" at each of time slots corresponding to a predetermined bit rate.
A plurality of bitstream data to be mixed are weighted for conversion into respective plural-bit digital data.
That is, by being weighted with plural-bit digital coefficients of optionally selected values, the bitstream data to be mixed are converted into respective plural-bit digital data, i.
e.
, data in PCM representation (pulse-code-modulated data).
The weighting digital coefficients perform not only a function of converting the bitstream data into PCM data but also a function of setting a desired mixing ratio.
Thus, the weighting degrees for the individual bitstream data may be variably set as desired