Most "24 bit" audio DACs have a lot less than 24 bits of real usable data due to the noise floor effectively burying the lowest bits in garbage, and I think the

Most "24 bit" audio DACs have a lot less than 24 bits of real usable data due to the noise floor effectively burying the lowest bits in garbage, and I think the noise increases at less perceptually noticable frequencies too. 24 bits is used for audio mainly because it's just convenient to standardise on that. I think they also have a lot more non-ideal behaviour in general than this, and they certainly don't have a 0.1% precision voltage reference because the precise output voltage range doesn't really matter for audio.