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Author
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Topic: do you use soft clipping mode on your amps ?
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David Baum
Film Handler
Posts: 90
From: Brussels, Belgium
Registered: Aug 2000
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posted 05-25-2002 07:04 PM
hisome pro amps offer this feature, which limits the clipping and even sort of increase significantly the unclipped power the amp can deliver. Do you guys use this feature ? Also, what power would you feed a "small cinema" equipped with JBL 3677 on the front and 2x4645C subwoofers ?
size is 8x15x4meters , 30seats ( small  ) .
I thought of 200watts unclipped on the fronts ( 8ohms ) and 800w on each sub. thanks
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Paul G. Thompson
The Weenie Man
Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000
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posted 05-26-2002 12:47 AM
No! Not in a theatre. I guess punk rock bands use soft clipping, but the music is so distorted nobody can tell the difference. Any clipping or limiting will produce an asymmetrical waveform. As an example, we broadcast AM stereo using the Motorola Format (L+R L-R) and the recommended setting on the stereo generator is ZERO asymmetrics because of distortion. FCC allows 125% positive peak modulation and 99% negative peak modulation in AM Broadcasting, but who cares? We are interested in broadcasting fidelity, and we are not interested in our coverage by exceeding 100% modulation in stereo broadcasting. Our AM Stereo transmitter has soft limiting, but since we do not want more than 100% positive peak modulation, we let the transmitter handle that instead of our processor. Clipping is clipping. I think Bobby Henderson and others in his profession might be able to address this better than I can. I have an Audio Technica 12-channel mixer, and it features soft clipping. I aviod that area as much as possible when I use it. I am after fidelity, not distortion.
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John Anastasio
Master Film Handler
Posts: 325
From: Trenton, NJ, USA
Registered: Sep 2000
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posted 05-26-2002 07:02 AM
Paul's right. Clipping is clipping. I managed the first AM stereo station in NJ and we also operated with the Motorola C-QUAM system. The GM insisted on getting those 125% postive peaks out of the transmitter and it was louder, but distorted as all hell, even though we weren't driving it into clipping. The distortion caused by clipping, whether it's soft or hard, is from added harmonics. In the case of just audio, once the waveform starts becoming more squared off, you're adding additional harmonics to the sound which give it that harsh, edgy sound. In the case of broadcasting, ALL of the information is transmitted in the form of sidebands and once you start clipping, all hell breaks loose as you generate sidebands all up and down the dial. Stay away from assymetrical waveforms and clipping, soft or hard. It's quality, not quantity that counts with sound...unless you're a heavy metal band.
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Frank Angel
Film God
Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
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posted 05-26-2002 02:16 PM
This idea of "soft clipping" came out of the butt of some marketing exec or ad copy writer who got wind of those techies who had begun this romantic love affair with "the tube sound." Of course none of them ever actually worked with real tube equipment, but it became the sexy buzz word with the new crop of the hip digital generation. Thus, an unholy aliance between young techies and young yuppie marketing people was formed and a deluge of equipment showed up in pro audio gear that claimed to either mimic the "tube" sound or actually used tubes in their circuits. And, of course, cost double the price of gear that didn't claim to be tube-like. There's a price to being hip.I started in the recording industry when tube equipment was still being used (Altec mixing boards, Pultec parmetric eqs, etc.) and I can tell you, no mixing or recording engineer I ever meet said, "gee, that distortion is ok because it's from TUBES." Distortion and clipping, no matter if it is coming from tube equipment or not, is crap and any engineer who is running his gear into it is an ass. If your amps are running near or at clipping in order to get Dolby level (or a good, punchy sound in the room according to your ears --the ultimate claibration instrument), then the system is under-powered and that needs attention. If on the other hand, the problem really lies in those imbicles who turn up the non-sync after hours, then before I would introduce some soft clipping circuit into the system and compromise the theatre sound, I would have anyone who messes with the system after hours FIRED. OK, so that's a bit draconian, and of course I don't want to be seen as the ogre in our happy theatre "familly" (gag me with a spoon), so I think I would opt for a threshold limiter/compressor rather than soft clipping on the amps. The compressor would treat normal levels transparently but would clamp on any level beyond the preset. Then I would go into the general manager and tell him he has to buy three Valley People thresshold limiter/compressors for about $2400, OR he can fire the after-hours crew. Which do you think he will choose? 
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