behavior difference for opus-tools and opus_demo

[wl3b10s]

i encode and decode a wav or pcm file with 16khz sample rate.

the result pcm of opus_demo binary by opus source code contains all frequency information between 0-8khz.

the result wav of opusenc opusdec binary by opus-tool contains frequency information between about 0-7.5khz.

why there is difference for the output audio's frequency information ?

thanks.