On Fri, 08 Feb 2008 00:56:16 GMT, Glen Walpert <g...@notaxs.com>
wrote:

>On Thu, 07 Feb 2008 17:51:38 -0500, John Popelish <j...@rica.net>
>wrote:
>
>>Winfield Hill wrote:
>>> John Larkin wrote:
>>>> I'd imagine that most capacitors add distortion, too.
>>> 
>>>  Our 2ppm may well be coming from the caps.
>>
>>Down at 2ppm, I would start worrying about resistor 
>>linearity, also.
>
>How about ppb instead of ppm:
>
>Linear Technology Magazine, Feb 94 pp 26-28 - LTMag_V04N1_Feb94.pdf
>at http://www.linear.com/lt_magazines.jsp
>
>"Using Super Op Amps to Push Technological Frontiers: an Ultra-Pure
>Oscillator
>
>An Ultra-Low-Distortion, 10kHz Sine-Wave Source for Calibration of
>16-Bit or Higher Analog-to-Digital Converters
>
>... The measurement of the harmonic distortion of this oscillator
>defies all of our resources, but appears to be well into the
>parts-per-billion range."
>
>And only 11 Op amps :-).
>
>ISTR another LT article on measuring the distortion of this oscillator
>using a 120? dB notch filter also designed with the "Super Op Amp"
>idea, but can't find it now.

Some references...

Newsgroups: alt.binaries.schematics.electronic
Subject: Re: opamp sine wave oscillator (SED)
Message-ID: <8...@4ax.com>

                                        ...Jim Thompson
-- 
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

On Sat, 9 Feb 2008 08:35:54 +1100, "Phil Allison"
<p...@tpg.com.au> wrote:

>
>"John Larkin"
>>
>>"Phil Allison"
>>>>>The famous Quad ESL63 electrostatic speaker has THD in the order of 
>>>>>0.03% at
>>>97dB SPL.
>>>
>>
>> How can that be measured?
>
>
> ** Huh ?
>
>  No idea how THD can be measured ?

No idea of how to measure THD in a sound wave to this sort of
resolution. Are microphones this good? If so, how do people measure
*them*?

>
>
>> Do you believe the number?
>
>
> **  No faith required, it ain't religion.

A lot of audio stuff seems to be. It sure ain't science. Do you
believe that you can buy cables that are six-nines pure copper?


John

"John Larkin"
 "Phil Allison"
>
>>>>>>The famous Quad ESL63 electrostatic speaker has THD in the order of
>>>>>>0.03% at 97dB SPL.
>>>>
>>>
>>> How can that be measured?
>>
>>
>> ** Huh ?
>>
>>  No idea how THD can be measured ?
>
> No idea of how to measure THD in a sound wave to this sort of
> resolution. Are microphones this good?


 **  True condenser ( not electret ) mics are easily good enough.


> If so, how do people measure *them*?


**  Tested with SPLs way above 97dB,  THD from the mic is still below 0.1 %.

It is easy to distinguish harmonics produced by the mic from those generated 
by a source by simply moving the mic further away  -  if the THD percentage 
falls,  then the mic is responsible for some or all of it.



>>> Do you believe the number?
>>
>>
>> **  No faith required, it ain't religion.
>
> A lot of audio stuff seems to be.


** As usual,  you confuse audiophool marketing drivel with audio 
engineering.



.......   Phil

John Larkin wrote:
> On Sat, 9 Feb 2008 08:35:54 +1100, "Phil Allison"
> <p...@tpg.com.au> wrote:
> 
>> "John Larkin"
>>> "Phil Allison"
>>>>>> The famous Quad ESL63 electrostatic speaker has THD in the order of 
>>>>>> 0.03% at
>>>> 97dB SPL.
>>>>
>>> How can that be measured?
>>
>> ** Huh ?
>>
>>  No idea how THD can be measured ?
> 
> No idea of how to measure THD in a sound wave to this sort of
> resolution. Are microphones this good? If so, how do people measure
> *them*?

One method is to assume that the microphone is time-invariant at small 
amplitudes, pick a repetitive signal, and do a lot of signal averaging. 
  By attenuating the sound with distance, the distortion polynomial 
(i.e. the Nth harmonic goes as amplitude**N for small amplitudes) allows 
you to distinguish between microphone and speaker distortion.

Not too much fun, but conceptually not too bad.

> 
>>
>>> Do you believe the number?
>>
>> **  No faith required, it ain't religion.
> 
> A lot of audio stuff seems to be. It sure ain't science. Do you
> believe that you can buy cables that are six-nines pure copper?
> 

I believe that some are _advertised_ to be six nines...of course that's 
before they went through the drawing die, not to mention the oxidation 
due to using thin strands...even assuming that people who would stoop to 
fleecing audiophools have the elementary honesty to _try_ to deliver six 
nines wire.

Cheers,

Phil Hobbs

On Feb 8, 9:35 pm, Phil Hobbs <pcdhSpamMeSensel...@pergamos.net>
wrote:
> John Larkin wrote:
> > On Sat, 9 Feb 2008 08:35:54 +1100, "Phil Allison"
> > <philalli...@tpg.com.au> wrote:
>
> >> "John Larkin"
> >>> "Phil Allison"
> >>>>>> The famous Quad ESL63 electrostatic speaker has THD in the order of
> >>>>>> 0.03% at
> >>>> 97dB SPL.
>
> >>> How can that be measured?
>
> >> ** Huh ?
>
> >>  No idea how THD can be measured ?
>
> > No idea of how to measure THD in a sound wave to this sort of
> > resolution. Are microphones this good? If so, how do people measure
> > *them*?
>
> One method is to assume that the microphone is time-invariant at small
> amplitudes, pick a repetitive signal, and do a lot of signal averaging.
>   By attenuating the sound with distance, the distortion polynomial
> (i.e. the Nth harmonic goes as amplitude**N for small amplitudes) allows
> you to distinguish between microphone and speaker distortion.
>
> Not too much fun, but conceptually not too bad.
>
>
>
> >>> Do you believe the number?
>
> >> **  No faith required, it ain't religion.
>
> > A lot of audio stuff seems to be. It sure ain't science. Do you
> > believe that you can buy cables that are six-nines pure copper?
>
> I believe that some are _advertised_ to be six nines...of course that's
> before they went through the drawing die, not to mention the oxidation
> due to using thin strands...even assuming that people who would stoop to
> fleecing audiophools have the elementary honesty to _try_ to deliver six
> nines wire.

There really was at least one wire maker that really did deliver on
the 6 nines pure claim.

I think they used ceramic or copper in all of the wire pulling
hardware.  Unlike the Phelpsdodge wire it didn't have to be pickled
before coating to remove the outer layer.

On Mon, 11 Feb 2008 17:24:23 GMT, Vladimir Vassilevsky
<a...@hotmail.com> wrote:

>
>
>John Larkin wrote:
>
>> Just digitally generate some sinewave numbers and pump them into a 16
>> or 20-bit DAC. Follow with an undemanding lowpass filter.
>> 
>> Add a second DAC that's the distortion stomper.  Sum it in, scaled down
>> by, say, 1000:1, and load it with distortion correction signals.
>
>It works only if the parameters of the first DAC are stable to the same 
>1000:1 precision.

I'd imagine that harmonic distortion would be pretty stable over time
and reasonable temperature. THD would be very low from a good 20-bit
dac, so the stomper doesn't have to tweak things a lot.

At higher frequencies, the output amps become a serious problem.

John