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This all brings us back to fm_login's original question. (By the way, fm_login, what's your first name?) Speaking from first-hand experience, I've found that the best broadcast analog stereo generators (e.g., the Orban 8100) easily pass greater definition than redbook (44.1/16) when your source is better than redbook. For this reason, if I could wave my magic wand, I'd have all FM radio stations use source material better than redbook (e.g., 24/96) and I'd have them convert their entire chains (including STLs, if digital) to that higher definition. But, unfortunately for me, it isn't going to happen. (I know, Dave O., you were probably holding your breath regarding this pie-in-the sky wish of mine!) We're lucky these days to have stations running uncompressed 44.1/16 all the way through their chains, with no sample-rate conversions nor down-conversions.

We do still have a few, smaller public radio stations around the country who are still running excellent sounding all-analog chains capable of conveying considerably more definition than redbook. (I think somebody in this forum posted a while back about such a station in San Francisco who have deliberately kept their chain all-analog, and who play vinyl, for that reason?) I personally like the sound of "old-fashioned" FM stations running very high-quality analog chains - and especially where they don't need STLs because their transmitters are co-located with their transmitters. (Not a very practical, realistic situation, but there are still a few such stations around the country.)

fm_login, my personal experience recording the best FM broadcast is as follows: If, to do it, you'll have additional A/D and D/A conversions in the path, I find that 20/96 (or 24/96) sounds a little closer (than 44.1/16) to the analog outputs of your best tuners that you're recording. However, per Dave O.'s point, if you're recording directly from a 44.1/16 (or 48/16?) digital output of the Accuphase, then I'd expect your best result by recording at exactly that rate (with no sample rate or bit conversions, nor any unnecessary additional A/D nor D/A conversions). This is my expectation, although I don't have an Accuphase T-1000 to try it first-hand.

Greg

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An FM signal contains the band limited and compressed analog conversion of an
analog input from whatever source. The FM channel resolution is less than a
16/44 digital equivalent. Can you explain what is the effect of having extra
bits and sampling rates in the digital representation of the source before
conversion, filtering and limiting? Where and how can the additional resolution
be hidden in the signal and then revealed in the output (this would be a
necessary condition for claims of the ability to hear the additional resolution
of the source)? The answer could have significant implications in information
theory (of course we are not talking about digital FM).

Al

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This whole thread makes me feel a bit like Alice. In any case I
can't resist adding my own prejudices and preconceptions to the
wisdom accumulating in this thread.

1. I agree that changing the sample rate of the source is unlikely to
have a positive impact on the quality. However increasing the bit
depth seems like it would be totally harmless, as long as you don't
later have to decrease it again, in which case I would think it would
have been better to have just left it alone in the first place.

2. Analog FM transmitters operate at a sample rate of 38 kHz, so the
T1000 is already making at least one sample rate conversion to output
a 44.1 or 48 ksps stream.

3. It was my perhaps misguided impression that many modern DACs
actually change the sample rate internally as part of their principle
of operation, even when feed from a source operating at their
"native" sample rate.

4. I have to wonder how many sample rate conversions are involved in
a modern "analog" FM transmission, considering the original source,
studio equipment, studio to transmitter link, audio processing at the
transmitter, and finally the digitally implemented "analog" FM
modulator in the FM transmitter? Can anyone enlighten me, and the
rest of us, about this issue? I also note that when a whole chain of
digital audio devices all operate at the same nominal sample rate,
some devices do what amounts to a sample rate conversion to convert
the input signal clock to match the phase and frequency of a fixed
internal sample clock.

John

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Al, somewhere below you made an excellent remark: The answer could have significant implications in information
theory. Sure the answer would not make any dense in information theory but the question itself bring a paradox to the table. There were a number of excellent comments made but I did not get any new “knowledge” or revelation from the thread. To summarize how I see the things it would be the following.

1)     There is not technical justification why 44/16 shall not be sufficient to handle FM signal

2)     In contrarily to #1 the reproduced FM signal is greatly benefited with extra 2 bit of resolution and 2X sampling rate (I use multibit A/D and D/A)

3)     In accordance with #2 the T1000 most likely restrict itself with 16 digital output but might have advantage by the fact that A/D output strange is not in signal path.

4)     T1000 might be at disadvantage by the fact that it needs to A/D composite signal at 192K. With higher sampling rate all problems of accuracy come to the play, particularly within the cheap implementation.

5)     It is not know how T1000 arrives to 16Bit from 24 bit if initial conversion. If they round the left over it then it is not good.

6)     It is not clear how the fast converter lives alone with RF stages in T1000.  I spend a LOT of efforts to isolate my digital form my RF. I do not see in T1000 those efforts. Would the T1000 give 75dB noise?

Anyhow, I think that market for FM tuner with digital output would grow, at least among the freaks who do FM. I use external A/D but if to do the MPX decoding on digital domain then the design begs to out digital.  I would like to hear more about digital decoders, this architecture and the prospect to outs 20 bit out of tuners.  I think the right way to answer it is to commission a digital multiplex decoder and feed it right from detector.  I very mildly consider it but… my RF playback, even as it is now, is way much capable then my Boston stations can furnish, so it does not make since to me. Still, the T1000 is available within my rich and I would like to decide for myself if it is intellectually “cleanly designed” unit.

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