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Underpowered amp, versus Brickwall?
Old 30th March 2019
  #1
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JayTee4303's Avatar
Underpowered amp, versus Brickwall?

Feed a power amp a signal it can't reproduce and the upper regions of the waveform disappear, neatly omitted, or clipped off, via a process called... clipping.

Amp and speaker damage can result.

So why doesn't a brickwall limiter risk similar damage to the downstream chain? Isn't it squaring off the waveform in a similar way?
Old 31st March 2019
  #2
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Wyllys's Avatar
 

Quote:
Originally Posted by JayTee4303 View Post
Feed a power amp a signal it can't reproduce...
Amplifiers do not "reproduce" signals. They amplify them, hence the term "amplifier". Loudspeakers reproduce sound.

Your basic question/premise is flawed.
Old 31st March 2019
  #3
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A limiter attenuates the entire signal, rather than clipping off the waveform peaks. You get the same basic waveform out, just less of it, rather than a different wave shape (with different and more upper harmonics).
Old 31st March 2019
  #4
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Clipping and limiting are actually the same thing ... if you have a “limiter” with an attack and decay time substantially faster than a single cycle of the input waveform ... you end up with clipping.

This is why compressors have minimum settings for hold and release time on the order of a handful of milliseconds ... too much shorter and they would start to follow the waveform to a significant degree on enough of the program marerial’s spectral content to start to behave as clippers.

For attack times you will see much shorter .... maybe 50-100 microseconds ... and this is actually fast enough to clip just at the threshold. Depending on the program material and ratio setting, this might be audible as a slight click .... essentially a burst of distortion as the front of the waveform is clipped.
Old 31st March 2019
  #5
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Isn't the idea of limiting to "limit" the sine wave amplitude before the top gets hacked off/squared?
Old 31st March 2019
  #6
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Quote:
Originally Posted by kirkus View Post
Clipping and limiting are actually the same thing ... if you have a “limiter” with an attack and decay time substantially faster than a single cycle of the input waveform ... you end up with clipping.

This is why compressors have minimum settings for hold and release time on the order of a handful of milliseconds ... too much shorter and they would start to follow the waveform to a significant degree on enough of the program marerial’s spectral content to start to behave as clippers.

For attack times you will see much shorter .... maybe 50-100 microseconds ... and this is actually fast enough to clip just at the threshold. Depending on the program material and ratio setting, this might be audible as a slight click .... essentially a burst of distortion as the front of the waveform is clipped.
Thanks! Not sure how I missed this, but got it now.

So...there could be some risk to downstream equipment, IF a guy was dumb enough to hear clicking and let it continue, but basically, if it sounds good, it is... yes?
Old 31st March 2019
  #7
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Quote:
Originally Posted by JayTee4303 View Post
So...there could be some risk to downstream equipment, IF a guy was dumb enough to hear clicking and let it continue, but basically, if it sounds good, it is... yes?
There’s no issue with limiter-attack clicking from an equipment standpoint .... after all, we’re talking about little bursts in the duration of 500 microseconds or so ... that is, the same length of a half-cycle of a 1KHz tone.

The whole issue with amp clipping is the fact that our systems have evolved to have headroom suited to music program material ... i.e HF drivers can get away with much less power-handling capability due to the fact that they tend to make much more sound for a given watt, and there’s less energy content in the music at higher frequencies. Likewise, woofers have excursion limits that are sufficient for the types of bass instruments that we put through them.

An amplifier driven into clipping doesn’t produce a signal that’s music-like in its energy content .... and thus it’s easy to drive music transducers beyond their design limits with such a signal.
Old 1st April 2019
  #8
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Quote:
Originally Posted by kirkus View Post
There’s no issue with limiter-attack clicking from an equipment standpoint .... after all, we’re talking about little bursts in the duration of 500 microseconds or so ... that is, the same length of a half-cycle of a 1KHz tone.

The whole issue with amp clipping is the fact that our systems have evolved to have headroom suited to music program material ... i.e HF drivers can get away with much less power-handling capability due to the fact that they tend to make much more sound for a given watt, and there’s less energy content in the music at higher frequencies. Likewise, woofers have excursion limits that are sufficient for the types of bass instruments that we put through them.

An amplifier driven into clipping doesn’t produce a signal that’s music-like in its energy content .... and thus it’s easy to drive music transducers beyond their design limits with such a signal.
Ok, thanks. My curiosity was both theoretical and practical.

Recording some live shows, no way to overdub, you take what you get.

A brickwall on the drums buss gets me where I need to go when gain, low ratio compression and EQ don't. Just a touch, not every hit, brings the bellcurve average up into harder hitting territory.

Good to know I'm not risking gear with this, thanks.
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