Taiyo Rawle wrote:
As for bit depth of audio systems where
analogue/digital conversion in either direction
occurrs then 24 bits is almost certainly enough as the
precision offered by greater bit depths will simply be
lost below the analogue noise floor. For example the
input level bargraphs of the echomixer program (Linux)
hover at -94dB or so using a 24-bit "professional"
soundcard (an Echo Mia MIDI) with open inputs -
nothing plugged into the analogue input jacks.
From this, the noise floor for this unshielded
internal PCI card is approximatly -94dB. It was
sandwitched between an AGP graphics card and a PCI TV
tuner card, so shielding could have bought this figure
down further.
Higher bit depths are beneficial to entirely digital
systems and within audio processing software, and some
people will want to transmit audio data across digital
lines without having to convert to 24bits or less.
Many argue that for most applications, bit depths
above 16 are lost below the imperfections of many
people's hearing anyway (and those of
electromechanical loudspeakers for that matter).
However, since the precision offered by 16-bit systems
is now below that of modern analogue technology, I
think that the ADC/DAC parts of a high-end audio
product should remain at 24 bits for now, unless the
target market demands something different, or if
someone invents an analogue audio system with a
dynamic range of 144dB or more.
You make some valid points. Perhaps 24 bit input and internal
processing bit depth is a good idea with a choice of 24 or 16 bit output.
However, there is one additional thing that needs to be considered with
an input ADC with more than 16 bits. The input buffer does have a noise
floor and you do NOT want to digitize the input buffer's noise because
this is adding noise to the signal negating one of the advantages of
digital. So, the LSBs which would only contain the input buffer noise
should be set to 0 somewhere along the line. I would do this at the
input ADC; it should be available for th 8 LSBs and could be set either
with software settable registers or with DIP switches. Obviously, this
(noise floor) will be dependent on the input buffer amp and the
impedance of the input that is is setup for.
--
JRT
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