Digital BW, The Print

It is considered conventional wisdom that the ear cannot hear frequencies
above and below a certain point, but that the existence of sound in those
frequencies has an audible effect on what we can. Two examples are called
intermodulation and harmonics.

Modulation can be used by piano tuners, they play two notes simultaneously,
and since the notes are tuned so closely (but not perfectly) they modulate
against each other, and by counting the modulations an experienced tuner can
tell exactly how far to adjust the string.

Two different notes widely separated will produce sum and difference
frequencies, and these can be even order or odd order harmonics.  People who
use old tube amplifiers, particularly electric guitar players, prize the
tube sound because it is primarily even order, which is considered pleasing
to the ear (within reason) as opposed to odd harmonics.

When cds first came out, a mental institution noticed that digital music did
not relax the patients anymore and they had to restore an all analog system.
(this was reported in the Syd-Aud-Con journal which is distributed to audio
and electro-acoustic engineers.)

Does anyone know what optical manifestations of this phenomena are?  there
must be a reason why Leitz lenses cost so much!

tom Robinson

> I liken this debate to the one that went on in the audio world some
> years ago. Studies showed that the human ear is not capable of hearing
> differentials more than 8 bits. They also showed the human ear is not
> capable of hearing frequencies below X and above Y ( forgive me I don't
> remember X and Y and their values aren't important).
> 
> This experiment was repeated many times with the same results. However,
> if you filter music so that no energy from frequencies below X and above
> Y appear and run a test to determine if people can hear the difference,
> they sure can. If you run test todetermine if people can tell the
> difference between complex music sampled at 8 bits vs. 12 bits, they
> sure can. In fact music sampled at 8 bits and limited to frequencies
> above X and below Y sounds pretty "hollow." It gets to the fidelity of
> the reporduction.
> 
> I think the same is probably as true for the eye as is for the ear.
> While humans are not suppose to be able to see beyoun 300 dpi, I would
> expect in a complex image they sure can tell the difference if it were
> printed at 300 or 360 or maybe even 720.
> 
> I always down sample to 720 and print from there.