[Elecraft] Audio Processing

[Joe Subich, W4TV]

> Any additional distortion or EQ applied AFTER processing usually
> results in a significant deterioration of the desired audio.

That may be (is) true in broadcast audio but not necessarily so
in communications audio.  The typical compressor and/or clipper
increases the amount of power producing low frequency components
at the expense of the intelligibility producing higher frequency
components.

For communications work it is generally worthwhile to equalize
after clipping/compression to increase the relative level of
high frequency components ... just like FM and (analog) TV
transmitters used to apply pre-emphasis to the processed audio
before it went to the modulator.

For an SSB transmitter, the key is a proper balance in the clipping.
Low frequency components should be clipped/compressed no more than
10 dB while high frequency components can often benefit from much
higher levels of clipping/compression.  In that regard, it is a
shame that modern amateur transmitters don't use a split band DSP
processor to allow balancing the 10 to 20 dB difference in levels
between the low and high formats of the human voice.

73,

    ... Joe, W4TV


On 4/22/2011 1:22 PM, amfmtv at aol.com wrote:
> I designed the processing parameters of the Omnia ONE AM broadcast
> processor, and have spent almost a half century adjusting broadcast
> audio.  My suggestion is to apply a "sensible" amount of compression
> and limiting to increase the perceived loudness level to the maximum
> amount the equipment is capable of and STOP THERE!  Adding more just
> muddies up the sound.  We should aim for a balance between ultimate
> "loudness", as well as sensible EQ to enhance intelligibility, and
> depth of processing.
>
> Specifically, for speech processing on the ham bands, you MUST start
> with a good microphone.  I have found that using about 7 - 10 db
> compression with a 3:1 compression curve, followed by 3 - 6 db of hard
> limiting, maximizes the perceived loudness, without reducing
> intelligibility.  In broadcast, 1 or 2 db of clipping will add a little
> bit more "punch", but cranking the clipping up more than that passes
> the point of usefulness quickly.
>
> Additionally, the transmitter should faithfully reproduce the audio
> sent to it.  Any additional distortion or EQ applied AFTER processing
> usually results in a significant deterioration of the desired audio.
> We hear a LOT of that on the air these days.
>
> To my ear, a well controlled but not overblown audio signal is both the
> easiest to listen to for long QSO's, but also has the punch to get
> through in crowded and/or weas signal conditions.
>
> 73
> Ted W8IXY
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