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"Audio Processing for HD Digital Radio"

7

700WLW

Guest
Like I said, it sounds the same as analog FM. Same processing, same sound...
 
That's a very old artical, it claims HD used the PAC Codec.

Ibiquity tossed out the PAC codec in favor of the HDC codec a few years ago.
 
audiophile. said:
Codecs all operate on similar principals...
Click to expand...
Yes, they do. They throw away much of the data, and decide for you what are the important parts.
They must, because moving as much data as is necessary to fully describe an analog waveform would require more bandwidth
than existing technology permits. An attempt to encode sine (actually non-sinusoidal) waves at frequencies above 15 kc, results in a curve that resembles a connect-the-dots-drawing with too few dots, and calls too much attention to the method.
In fact the codec must presume the wave is sinusoidal, when real audio seldom is, which is why audiophiles complain about the lost phase relationship in CD audio.
It seems counter-intuitive, but if they did NOT do this, very few people would find the result acceptable.
It is the same reason many of the first generation CDs sounded awful. The second or third generations had the upper end
rolled off so the remaining audio was smoother.

This should be done any time audio is encoded to a digital format.
And the lower bitrate, the more upper end needs to be rolled off in order for the result to sound acceptable.
At some point, it is also necessary to begin rolling off the low frequencies, too, to give perceptual balance.
AM radios with intentionally limited audio upper end need to have the bass frequencies reduced in order not to sound muddy.
I wish more streaming audio sources respected these sonic realities.
 
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