On Thursday 24 February 2005 02:18, Alexander S. Yurkov wrote:
Dear Alberto,
On Wed, 23 Feb 2005, Alberto di Bene wrote:
> Do really exist A/D converters capable of 24-bit resolution at 30
> MHz bandwidth ?
Why one need 24-bit? Though 16 bit is adequate for most SW,MW,LW
recievers. 16 bit yelds abt 90 dB dynamic range (every bit exept
sign bit yelds 6dB).
This means that 1 bit give a sufficient MDS? The recovered audio is
ON/OFF tone?
But this is dynamic range if there is no
filtering. When you make banwidth narrow by DSP then dynamic range
will be improved because noise decreases. If frontend sampling rate
is, say 100 MHz (there is such an ADC) and bandwidth of DSP filter
is about, say 10 kHz this yelds 40 dB of noise decreasing. Thus RX
dynamic range to be about 90+40=130 dB! Realy DD is not 130 dB of
cose. But it much less due to analog (!) effects in ADC absolutely
similary as in conventional analog RX. This is not digital effect!
But without a single channel roofing filter a 130 dB outband signal
make the AD converter overload, despite any sampling rate. Or not?
I have some unanswered question:
1- How many bits are needed for a good audio reproduction, i.e. a S/N
ratio of 10 dB with some voice dynamics? Telephone signals usually
are sampled 8 kHz 8 bits for a telephonic quality (with no
compression). May be that 4 bits are sufficient but 1 bit I don't
think.
2- Those bits are to be taken in account for calculating the dynamic
range? i.e. 16 - 4 = 12 bits =72 dB dynamic range.
73 de Claudio, ik2pii
-
Claudio Pozzi - Happy Linux User - http://www.qsl.net/ik2pii
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