Stephanie Weil wrote:
On Aug 27, 12:38 pm, Bart Bailey wrote:

Orban's Opti-Mod I think it's called, and station personnel that can't
seem to resist adjusting them for maximum smoke.

Processors were always set "hot" way before IBOC came on the scene,
and I never heard station audio clip and distort the way it does now
on the analog side of AM HD. Reducing the available bandwith for
analog to +/- 5 khz to shoehorn the digital portion sure hasn't helped
either.

The whole idea with HD is that you have to back off on the processing
a bit. You can't overdrive digital the way you can with analog and
have it come out sounding good. It's like slightly overdriving a
recording on cassette tape vs. Minidisc. If you try it with Minidisc,
you hit a brick wall and everything above that starts sounding like so
much mush.

Stephanie Weil
New York City, USA



Clipping has been part of audio processing since the early days of
audio processing. It's usually inaudible. AM processing has been using
'smart' clipping for awhile, now. Smart clipping is not quite as
hard--rounded edges--but for a number of years CRL openly hard clipped
the composite baseband and let the **** fall into the filter where it may.

And not all analog clipping is that objectionable. It adds even order
harmonics, which are pleasing to the ear. If over done...well, that's
another story...but lightly, it can be a good thing...

One of the problems we have with digital audio, is the number of
analog engineers applyin analog thinking to digital audio. And this
applies to both recording and live audio, as well. You're right, digital
audio is a brick wall at '0', and anything beyond that becomes some
serious trash. Analog engineers, especially in the recording industry,
routinely try to recreate 'tape compression' at the top end, by driving
preamps and other pre conversion electronics mildly to their top end.
Especially if they're using tube preamps. This takes a delicate hand.
But who's that delicate is broadcasting, today? Not many.

The most common complaint I hear about HD reception, today, and this
applies to both AM and FM, is the audio quality isn't what is expected.
It's not CD quality, which according to Philips and Sony was only
supposed to be medium-fi in the first place. And the HD audio is nearly
always loaded with some kind of distortion artifact resulting from
trying to pack 5 lbs in a 4 lb bag.

Truth is, the very reasons we developed audio processing in the first
place still apply to the digital audio--limited headroom and the attempt
to control clipping distortions while retaining compelling listening.
Simply going digital is not changing those needs. While digital usually
has deeper dynamic range, on the soft end, there is still a finite,
limited ceiling at the max end, and that's where the most objectionable
distortion is. So, the same needs for processing still apply. Albeit in
different areas, with different parameters.

To provide compelling listening in the digital stream, engineers MUST
provide the proper dynamics and spectral controls.

But that costs money. And most HD streams are not self supporting.
And with Radio facing performance royalty payments, that's not likely to
change any too soon. Another reason why the HD battle is upstream.

The hard truth is that Radio in the main, isn't playing HD the way it
needs to be played to maximize it as a resource. Some are. There are
some very good sounding HD streams. But most aren't.

And they aren't likely to start. It's too much work, for too little
revenue return on the investment.