Amp freq response: Sonos vs Peachtree

  • 12 April 2019
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Perhaps a stupid question: how would you see this headroom unless the volume control was recalibrated as Sonos seem to have via software for the Sonos Amp? But I agree that we need to see other responses.
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I was comparing peak amplitude before and after the filtering. The link I provided shows how to do this in Audacity. I was using jazz and classical music samples from 2L. I wouldn't be surprised if other types of music gave different results.
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Something I find interesting... if you apply a 100Hz high pass filter to some modern popular music files, the peaks actually increase. So files with peaks just shy of 0dB go into clipping. If you attenuate the original file by 3dB, then HP filter it, you can see that the peaks actually increase by quite a bit. All of this convinces me that there is no reason for Sonos to a apply a 3dB bump with their sub crossover.

Peter - sorry if we (especially me) are derailing your thread!
Something I find interesting... if you apply a 100Hz high pass filter to some modern popular music files, the peaks actually increase. So files with peaks just shy of 0dB go into clipping. If you attenuate the original file by 3dB, then HP filter it, you can see that the peaks actually increase by quite a bit. All of this convinces me that there is no reason for Sonos to a apply a 3dB bump with their sub crossover.
I think you have discovered the Gibbs Phenomenon. Some people refer to this as "overshoot", and it is related to "ringing". Usually it is observed when low-pass filtering, but it can also happen with a high-pass filter. If the filter has too high a Q factor (i.e. it is a steep filter), there can be overshoot for frequencies close to the filter cutoff. The first plot below shows the Sonitus EQ in Cakewalk by Bandlab (used to be Sonar, similar program to Audacity). It has a Q of 1.6 and simply cuts out low frequencies. The second plot pushes the Q up to 3, which boosts some frequencies while still cutting out most of the low ones.





Peter - sorry if we (especially me) are derailing your thread!
No worries - it's all interesting discussion.
Does this then bring to light an undisclosed feature of the Amp? That it will deliver sound levels that are higher across the board by 20-30% if bonded with the Sonos Sub or with a third party Sub of similar power? That is no trivial feature to have. And I don't think that too many legacy HiFi amps can boast of this capability; all they can claim is what comes from the Sub - frequency extension at the lower end.
So, does anyone want to take a shot at answering this?
Does this then bring to light an undisclosed feature of the Amp? That it will deliver sound levels that are higher across the board by 20-30% if bonded with the Sonos Sub or with a third party Sub of similar power? That is no trivial feature to have. And I don't think that too many legacy HiFi amps can boast of this capability; all they can claim is what comes from the Sub - frequency extension at the lower end.
So, does anyone want to take a shot at answering this?

Sure. I think you're right. It's making optimum use of its 125W power. Of course, it's only relevant if running the Amp at maximum volume is not loud enough. And I have to say, it's already pretty loud at max! I suspect that all other amp manufacturers could choose do the same thing with the power they save by hiving off the low frequencies to a sub.
Extra power is always useful - to not just run at max, but for better handling music with high dynamic range. At max, even a Connect Amp is pretty loud, but I wonder if it could not better use this feature. If Sonos ever gets around to giving it that.
And when you say other amp manufactures could do the same, I don't suppose you are referring to the many that use electro mechanical volume controls.
Extra power is always useful - to not just run at max, but for better handling music with high dynamic range.
What's the science behind that idea when it comes to Class D amps? It might be true for more traditional amps where the distortion goes up as the volume increases. But I believe Class D amps go the other way (based on limited reading).

And when you say other amp manufactures could do the same, I don't suppose you are referring to the many that use electro mechanical volume controls.
I hadn't thought about whether the volume control method would make a difference or not. Perhaps non-Class D amps would be trickier, but I don't know enough about amps to really be able to offer an opinion.
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I think you have discovered the Gibbs Phenomenon. Some people refer to this as "overshoot", and it is related to "ringing". Usually it is observed when low-pass filtering, but it can also happen with a high-pass filter. If the filter has too high a Q factor .

There is also this to consider (filter causing constructive effect).
https://www.soundonsound.com/sound-advice/q-why-do-my-mixes-clip-when-i-apply-high-pass-filter
FWIW I was using a 6db filter in Audaicity for a gentle rolloff on the HP filter like I would think a crossover would use.

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