Suppose a digital music file goes through a dac, then an adc. Both units would be generally accepted as high quality. Would the final file be bit perfect to the original?Extremely unlikely. No DAC is perfect, and no ADC is perfect. The only way to maintain bit perfect accuracy is to keep the data entirely in the digital domain, while applying no processing to it that might change the value of any of the bits. Even then, timing fluctuations ("jitter") caused by electrical noise or any of many other possible effects, as well as DAC inaccuracies, may audibly degrade the quality of the signal when it is ultimately converted to analog.
Regards,
-- Al