[BC] CD vs LP

[RichardBJohnson at comcast.net]

Dithering improves RESOLUTION, never DYNAMIC RANGE. Dynamic
range is the ratio between the maximum number of codes (the maximum
level) and the minimum --which I even pretend is zero. The documentation
is absolutely positively wrong and I worked 20 years for the guy, now
retired, who invented A/D converters and who has over 500 patents on
them --who drummed this into our heads -- Bernie Gordon.

If you take your test setup and keep reducing the input level by some
known attenuation step, the output should be reduced by the exact
same step until you get to residual noise. The residual noise will
always REDUCE the available dynamic range, never increase it.

It your measurement setup doesn't have a 1:1 correlation between
the input level and the output level, then you have proved a nonlinear
system exists. If you have a system in which this nonlinearity exists,
then you have a quantization problem (missing codes) at low levels.
This makes the system act like it has a built-in squelch and there
are papers out there that pretend that this is good. It's like cross-over
distortion in early SS amplifiers. You keep reducing the level and
suddenly there is nothing --a great S/N.

--
Cheers,
Richard B. Johnson
Read about my book
http://www.LymanSchool.org


 -------------- Original message ----------------------
From: Robert Orban <rorban at earthlink.net>
> If you measure the maximum sinewave level that the channel can 
> accommodate using an RMS detector, you also need to measure the 
> dithered noise floor using an RMS detector. Just to verify, before 
> posting this message I measured the output noise floor of an Optimod 
> 6300 in TONE mode with dither turned on as -92 dBfs RMS and measured 
> the maximum undistorted sinewave output as 0 dBfs RMS on the same meter.
> 
> The 6300, like all Optimods, uses first-order highpass TPDF dither. 
> To make sure that the dither was working as expected to decorrelate 
> the noise from the signal, I also checked the THD+N with a -40 dBfs 
> sinewave. It was -52 dBr, where the reference is -40 dBfs. None of 
> these measurements support your claim that the dynamic range is only 
> 87 dB for 16-bit digital.
> 
> Meter was an NTI Digilyzer.
> 
> Please see the references in the Dunn paper, particularly the 
> Lipshitz and Vanderkooy papers (refs [2] and [3]), which are 
> considered classic.
> 
> At 04:49 PM 9/22/2008, RichardBJohnson at comcast.net wrote:
> >Yes I know and it's wrong. It's often quoted as 20 log10 * 65536 for
> >65536 codes of a 16-bit number, which is about 96 dB.
> >I show how it is wrong because it can't possibly be greater
> >than 20 log10 * 32767  (90 dB) even if you consider the peakshitz &
> >value (incorrectly) as having something to do with dynamic
> >range.
> >
> >--
> >Cheers,
> >Richard B. Johnson
> >Read about my book
> >http://www.LymanSchool.org
> >
> >
> >  -------------- Original message ----------------------
> >From: Robert Orban <rorban at earthlink.net>
> > > At 08:09 AM 9/22/2008, RichardBJohnson at comcast.net wrote:
> > > >0.707 * 32767 =  23,166 (convert peak level to RMS)
> > > >20 log10 (23,166) = 87 dB
> > > >
> > > >Eighty-seven decibels dynamic range  is much greater than
> > > >typical analog audio circuitry that almost never exceeds
> > > >80 dB over a 20 kHz bandwidth, that it should not be the
> > > >limiting factor in a high-fidelity system.
> > >
> > > Dunn says it is 93.3 dB with flat  (white) TPDF dither in the AES
> > > Convention presentation:
> > >
> > > www.nanophon.com/audio/dynrange.pdf
> > >