HI use BASSmix
ExampleAdd a channel to a mixer, delaying the start by 1 second and limiting the duration to 2 seconds.
QWORD start=BASS_ChannelSeconds2Bytes(mixer, 1); // delay
QWORD length=BASS_ChannelSeconds2Bytes(mixer, 2); // duration
BASS_Mixer_StreamAddChannelEx(mixer, channel, 0, start, length); // add the channel