| Author |
Message |
    
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1458
Registered: 6-2004
| | Posted on Sunday, January 28, 2007 - 8:22 am: | 
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Can someone explain to me why asymmetric voices cause problems with AM modulation? I've read lots of references to this issue, but I've never come across an in depth explanation or an oscilloscope trace showing the actual problem.
Aack! - Bill the cat
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Tech833
Moderator
Username: Tech833
Post Number: 1598
Registered: 8-2002
| | Posted on Sunday, January 28, 2007 - 10:23 am: |
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When positive peaks greatly outpace negative peaks, without some limitation, adjacent channel splatter becomes a problem. The audio IMs against the carrier and harmonics grow at an expotential pace. Looks great on a wattmeter, but terrible on the spectrum analyzer.
Huge positive peaks CAN be done correctly, but I have never seen it done well on consumer 2-way gear. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1459
Registered: 6-2004
| | Posted on Sunday, January 28, 2007 - 11:44 am: |
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I don't understand how that's possible. Shouldn't the modulation be symmetric? Is there some kind of effect that causes the modulation to become asymmetic?
Maybe I don't understand what an asymmetric voice is? I thought it was unbalanced voice - one with too much bass or too much treble.
Aack! - Bill the cat
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Tech833
Moderator
Username: Tech833
Post Number: 1599
Registered: 8-2002
| | Posted on Tuesday, January 30, 2007 - 9:06 am: |
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No. Human voice is almost all positive peak. Your vocal chords can only 'push' sound waves, they don't 'pull' them. Therefore, electronic means of voice to electrical conversion naturally contains mostly positive peaks. A phase rotator can make voice symmetrical, most professional microphone audio processors do include a phase rotator which makes mic audio 'louder'. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1460
Registered: 6-2004
| | Posted on Tuesday, January 30, 2007 - 9:21 pm: |
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I've been reading what I could find about phase rotation, and what little I've found and understood is that negative peaks are the problem, and phase rotation is used to change the negative peaks to positive because it's better to deal with than negative peaks - especially on AM.
Is there something you would recommend that would explain it better? Either I can't find good information on the web, or I don't understand what I've read.
Aack! - Bill the cat
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Tech833
Moderator
Username: Tech833
Post Number: 1601
Registered: 8-2002
| | Posted on Sunday, February 04, 2007 - 10:44 am: |
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Eddie, the only time negative peaks are the problem is if your wired your balanced audio backwards. Voice picked up by a microphone contains almost no negative peaks.
I read some great information in an Orban Optimod equipment manual once, but I do not recall which piece of equipment it was. Try the Orban website manual download area for some info. |
