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Junior Varsity
Help me understand system limiting- setting it
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<blockquote data-quote="Nick Hickman" data-source="post: 26636" data-attributes="member: 556"><p>Re: Help me understand system limiting- setting it</p><p></p><p>Hi David,</p><p></p><p></p><p></p><p>When limiting the power applied to a driver, it's usual as you say to use slower attack times for lower bandpasses. The attack time is often made inversely-proportional to the lowest frequency in the bandpass. This is related to the thermal time constant of the driver (that's how quickly it heats up and cools down) and, as you say, the length of a cycle. If the attack is too slow, the driver will have cooked before the limiter acts but, if it's too fast, it will distort the waveform.</p><p></p><p>There may be a terminology issue here. A "peak limiter" can mean a limiter (i.e. a compressor with a high or infinite ratio) with a detector that looks at peak signal level. When the detector sees levels over threshold, it starts to gradually ramp down the gain at the attack rate. When the detector sees the signal go back below threshold (and after any hold time has expired), the gain is ramped back up at the release rate. You're thinking of "peak limiter" in the sense of hard-limiting with zero overshoot. That can be done with a limiter as above plus a clipper to clip off the overshoot until the limiter has had chance to reduce the gain. The brief clipping is usually inaudible. In the digital world, it can also be done by having the detector "look ahead" by delaying the main signal so that the limiter can start reducing gain <em>before</em> the signal goes over-threshold.</p><p></p><p>Why are you concerned about peaks? Do you have an amplifier whose peak power is much larger than the driver can handle? If so, fair enough. If not, the amplifier voltage rails provide a pretty good clipper, and what you really need may be an RMS limiter. Any driver can be relied upon to handle short peaks at least 6dB above its power rating (i.e. four times power), and quite probably higher.</p><p></p><p>Nick</p></blockquote><p></p>
[QUOTE="Nick Hickman, post: 26636, member: 556"] Re: Help me understand system limiting- setting it Hi David, When limiting the power applied to a driver, it's usual as you say to use slower attack times for lower bandpasses. The attack time is often made inversely-proportional to the lowest frequency in the bandpass. This is related to the thermal time constant of the driver (that's how quickly it heats up and cools down) and, as you say, the length of a cycle. If the attack is too slow, the driver will have cooked before the limiter acts but, if it's too fast, it will distort the waveform. There may be a terminology issue here. A "peak limiter" can mean a limiter (i.e. a compressor with a high or infinite ratio) with a detector that looks at peak signal level. When the detector sees levels over threshold, it starts to gradually ramp down the gain at the attack rate. When the detector sees the signal go back below threshold (and after any hold time has expired), the gain is ramped back up at the release rate. You're thinking of "peak limiter" in the sense of hard-limiting with zero overshoot. That can be done with a limiter as above plus a clipper to clip off the overshoot until the limiter has had chance to reduce the gain. The brief clipping is usually inaudible. In the digital world, it can also be done by having the detector "look ahead" by delaying the main signal so that the limiter can start reducing gain [I]before[/I] the signal goes over-threshold. Why are you concerned about peaks? Do you have an amplifier whose peak power is much larger than the driver can handle? If so, fair enough. If not, the amplifier voltage rails provide a pretty good clipper, and what you really need may be an RMS limiter. Any driver can be relied upon to handle short peaks at least 6dB above its power rating (i.e. four times power), and quite probably higher. Nick [/QUOTE]
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