how can I confirm 24 bits is being played and not down sampled 16 bits?
in Playback>Output, Output format data is still 16 bit and it can not be changed as it is grayed out. […] How can I confirm 24 bits is being played and not down sampled 16 bits?
Bit depth is 32bit - as handled by DirectSound in Windows 7. Foobar sends 24 bit data to DirectSound engine of your OS and everything there is handled by DS/device drivers with 32bit precision or lower (like 24bit), accordingly to your soundcard specification and capabilities. Assuming you are using DirectSound output of course
@ Kohlrabi: If he has "16 bit" that is selected but grayed out it may mean that he really has output fixed at 16 bit. Additionally "Always dither" checkbox is unchecked and grayed out here, on mine PC.
He has 24 bit file and 24 bit capable soundcard - why "degrade" it to 16 bit if it can be played with full available quality?
A] You must set the digital volume slider in FOOBAR to -100DB.
If you select your soundcard which as you say has ASIO drivers, foobar2000 negotiates with the ASIO drivers and uses the bit-depth they report. Bit depth has to be configured in your ASIO configuration panel.
Actually if you use the Digital volume control inside Foobar then the ASIO driver gets less then 24Bit.