[P A U L]

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Do I need 16 or 24 bits ?

As a general rule of thumb the microphone is much more important than the use of 24 bits so if your budget is tight, spend more on the mic and less on the deck and storage. Simply stated the recording cannot possibly achieve better quality than the microphone is capable of delivering.

The other significant consideration is the mic preamp. Many preamps for popular 24 bit machines use chips and capacitors that have artifacts that are down only 85dB to 95dB. If the signal you are recording is from a microphone, it is typically down 40dB to 50dB so the resulting dynamic range is 85dB to 95dB less 40dB to 50dB or not very good ! A 16 bit A/D chip has a dynamic range of 96dB, more than enough for these preamps. You want as much of a difference between the desirable signal and the residual noise and distortion of the preamp as possible. With an input signal down at -40dB to -60dB you need microphone preamp artifacts to be as low as possible as the preamp amplifies both the desirable signal and the undesirable artifacts. We use preamp chips with THD+N down from 110dB to 130dB that cost as much as 50 times what the stock chips cost.

The result of low grade parts in a mic preamp is performance that is not even 16 bits, this makes 24 bits with a poor preamp of questionable value. A typical 24 bit machine's preamps Spurious Free Dynamic Range is no where near the 144dB dynamic range of 24bits and most do not even achieve 16 bit quality. Even some of the best op amps, the chips used in digital recorders, have no more than 120dB SFDR and most stock machines typically use chips that have a SFDR of less than a 96dB.