On 3/6/2015 1:06 PM, John Davis wrote:
On 2/26/2015 3:55 AM, AndyW wrote:

MP3 is lossy, it cannot be used to reproduce the original but it does
not 'remove' signal, they get lost.

IIRC some sound encoding deliberately removes some frequencies if the
are low amplitude and are close to a higher amplitude frequency.

Loses is passive, the data just gets lost. Remove implies some active
removal of data.

All of what you type is true yet MP3 is good enough for most music
lovers (The true "Golden Ears" do not like it but not many are that
good) I can occasionaly hear the difference but not always.


Both MP3 and CD use 16/44 (16 bits, 44kHz sample rate) formats. The
difference is that the CD will have the entire signal stored, while MP3
will remove some of the signal which is not as important as others.

If you play an MP3 and a CD on any decent (not even audiophile)
equipment, the difference is noticeable, even to a non-audiophile. And
the difference between MP3 and high resolution 24/192 is even greater if
you're playing music with wide frequency and volume ranges, such as much
classical music. But you won't hear that much of a difference between
MP3 and 24/192 on a many rock songs

The major advantage of digital over analog modulation is that the
computer's "ears" (The de-mod unit) are way more discreaning than my ears.


Computers are lousy playback mechanisms. The frequency response of the
amplifier is nowhere near flat, and the speakers generally stink. It
would be better if you hooked up a decent set of stereo speakers - but
even then a cheap amplifier will outperform virtually any computer.

First. Under noisy low signal conditions,,, Most of the noise is lost
simply because it is not present at the proper time,, With analog none
of it is lost you need to spend heavy duty effort to filter it out.. But
with DSP you look for 1 or zero at the right time, noise that happens
when you are not looking... is ignored.. And with protocol some errors
caused by noise get corrected, others can not be but in some cases a
re-peat of the packet is requested and delivered.


Noise is like any other part of the signal. If you have a 1kHz noise
spike, it will be present for approximately 1ms. That is plenty long
for any ADC to detect it. And if the noise pulse is shorter than the
sampling time, it would be of too high of a frequency to hear, anyway.

Plus, DSPs do not look at amplitude. They measure the instantaneous
slope of the signal and store it as a digital value depending on the
number of bits, i.e. 16 bit samples would have 2^15 negative slope
values and 2^15-1 positive slope values (plus zero slope). By
recreating the instantaneous slope that is stored digitally, the DAC
converts the digital signal back to an analog signal.

And digital error-correction protocols have nothing to do with the
digital signal itself - only the transmission of it from one system to
another. But that is an entirely different subject.

Far less power is needed to make the trip,, Digital signals can travel
farther on less power all because of the above. It truly is an amazing
way to chat,, I have used both digital and analog or many years, and
where as with analog, as the sigal goes down the amount of operator
skill to hear the voice goes up, way up, and more and more folks start
wonering what it is I am hearing, cause they sure can not hear it, but I
seem to be writing down good inormation.


Yes, I understand that. I was working RTTY back in the 60's, and it was
amazing how you could get good copy on a signal you couldn't even hear
in the noise. Of course, the narrow filters used on the audio signal
made a big difference - just like a narrow filter helps pull a CW signal
out of the mud.

With digital you are there, or you are not, and "There" means it sounds
like you are sitting beside me. (Perhaps that is why I operate SSB, I
like to keep the skills honed a bit).

Yes and no. Digital does for the most part work or not work. However,
when you get into marginal conditions, it can get iffy, with some
packets lost and not recoverable.

Probably the easiest way to see this is watching a digital TV signal.
When the signal becomes marginal, the picture will start to display junk
in random small spots on the screen, similar to snow (known as
pixelation). Satellite TV users have seen it during heavy rain, and
even cable TV users can see it when a network's satellite link suffers
from a marginal signal.

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Jerry, AI0K

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