Hi Johan, Your idea may well work! (I think there is something similar used for processing XM satellite radio service in the USA called Neural Audio - see www.neuralaudio.com)
For narrow band speech such as used for communication, standard audio compression (possibly two band) and RF clipping (which eliminates harmonic distortion but leaves IM distortion) would provide the most decrease in peak-to-average ratio, and thus increase loudness. The phase scrambling techniques though are really the 'Icing on the cake' so to speak just squeezing the last dB or so of loudness gain from the system. Also, SSB hasn't usually got such a distinct overload point as does AM - By the way, the RF clipping is sometimes done at baseband (Orban for their Shortwave version of their analogue Audio processor, the 9101B) used a Hilbert transformation to do this with audio directly. Using similar techniques in DSP should be a lot easier to implement 73's Andy ----- Original Message ----- From: "Johan Bodin" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, February 03, 2007 3:23 PM Subject: Re: [soft_radio] Re: Tecnical discussion > Hi Andy, > >> In broadcast audio processing group delay is deliberately changed - the >> audiio is run through allpass filters that are typically third order. The >> reason for this is that it tends to make an assymetrical audio signal >> more >> symmetrical. (male voice is often very assymetrical). > > If it works for AM I think it could be useful for speech processing in an > SSB transmitter as well. If some harmonics could be phase shifted with > respect to the fundamental, maybe tallest narrow peaks in the time domain > (typical for some male voices) could be smoothed out thus allowing > increased "talk power" for a given maximum PEP without introducing > non-linear distortion (like clippers)? Hmmm.. Interesting. If some delay > can be tolerated, some clever DSP algorithm could "look ahead" in the > audio stream and tweak a number of allpass filters on-the-fly? > > Just a wild idea... > > 73 > Johan, SM6LKM > > > > Yahoo! Groups Links > > >
