no, its not
if so 24 bit files would be 256 times larger than a 16-bit recording
its really (for 48K audio)
16 bit: 48000 samples/sec x 2 channels x 16 bits/sample = about 1.5 Mbits/sec
24 bit: 48000 samples/sec x 2 channels x 24 bits/sample = about 2.3 Mbits/sec
the advantage is of course increased headroom, each bit is 6 dB or resolution
16 bit = 96 dB of dynamic range
24 bit = 144 dB of dynamic range.
The best gear out there tops out at about 120 dB of dynamic range, which means that:
a) you cant capture all of the sound in 16 bits.
b) you can capture all of the sound in 24 bits, even if your peaking at about -24dB
while people say 'theres more headroom when you record in 24 bit', this headroom DOES NOT translate to 16 bit unless you normalize it while in the 24 bit realm
in other words, take a 24 bit recording that peaks at -24 dB. the dynamic range is 120 dB. if you convert this to 16 bit with no normalization, your new dynamic range is 96-24dB=72 dB (not so good).
If you were to normalize the 24-bit file to 0 dB, youd still have a dynamic range of 120 dB (you amplified the noise too), then when you dither and convert it to 16 bit, you have the full 96 dB of headroom.
i hope that makes sense.
To understand why there is better detail and dynamic range, understand that 16 bit is 2 to the 16th power; 24 bit is 2 to the 24th power.