In audio-decoder apparatus, a circuit substrate common to a 2-channel model
and a 5.1-channel model, on which a decoder and a D/A converter with
built-in PLL are installed, and which has installing portions and for
enabling installation of D/A converters without built-in PLL. The line
connection modes of signal lines connecting the output terminal of the
decoder to the input terminals of each D/A converter can be changed by a
switching apparatus, corresponding to the channel model, thus it becomes
possible to realize D/A converters without built-in PLL having better
audio performance under a line connection mode desired for an improved
audio performance. Therefore, a good audio performance can be secured,
while a common circuit substrate can be used for a variety of channel
models, which is advantageous in view of fabrication cost.