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HPF (I think) demonstration on youtube?


chyc

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6 minutes ago, chyc said:

Am I right in thinking that class d amplifiers get this HPF for free, or at least the amp's designers would need to explicitly build an amp to generate subsonic frequencies, which would make no sense?

 

 

 

The basic Class D power stage works down to DC - the input comparator will just generate a PWM signal to output a DC level proportionate to the input signal.

 

This means the frequency response needs to be designed in. It can be a simple RC filter or a complex one

 

https://www.allaboutcircuits.com/projects/how-to-build-a-class-d-power-amplifier/

 

 

 

 

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20 hours ago, Matt P said:

according to  @Jus Lukin it's actually -12db/Oct fixed at 30hz plus -12db/Oct variable.  (as quoted on the massive HPF filter thread on page 15) HERE

 

Matt

I think the Mini HP Vong is just a single -12db/Oct filter, but the Vong-Filterung has the fixed -12db at 30hz plus variable from 30-140hz.

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On 15/09/2021 at 22:12, Dood said:

 

Yup! As you say, My fave amp has a variable HPF and LPF, some of the major effects units I have owned such as Helix and Quad Capture have HPF blocks in them, there are SO many amplifiers on the market that have HPF's in them by design - guitar distortion pedals definitely have them in as a "pre-EQ" requisite (hence why you don't get much low end out for bass out of some). 

 

I agree that it isn't a gimmick, but, like signal limiting and over heating/short-circuit circuitry, an HPF is useful feature to have on board. Especially for those scallywags in rehearsal rooms that crank the bass control up to the max lol. 

Indeed.  This is one of the reasons that I bought the Helix.  It's worth the admission fee for the global eq section alone IMO. Okay, I might be exaggerating a little, but it's a 3 band fully parametric eq that includes hpf and lpf (labelled as low/high cut).  There's also a myriad of different eq block to use in presets, including a parametric that is the same as the global eq, graphic eq, shelving, tilting an a simple low/high cut block that I use in nearly every patch..

 

No longer do I fear dodgy room acoustics!

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On 15/09/2021 at 22:12, Dood said:

 

Yup! As you say, My fave amp has a variable HPF and LPF, some of the major effects units I have owned such as Helix and Quad Capture have HPF blocks in them, there are SO many amplifiers on the market that have HPF's in them by design - guitar distortion pedals definitely have them in as a "pre-EQ" requisite (hence why you don't get much low end out for bass out of some). 

 

I agree that it isn't a gimmick, but, like signal limiting and over heating/short-circuit circuitry, an HPF is useful feature to have on board. Especially for those scallywags in rehearsal rooms that crank the bass control up to the max lol. 

Indeed.  This is one of the reasons that I bought the Helix.  It's worth the admission fee for the global eq section alone IMO. Okay, I might be exaggerating a little, but it's a 3 band fully parametric eq that includes hpf and lpf (labelled as low/high cut).  There's also a myriad of different eq block to use in presets, including a parametric that is the same as the global eq, graphic eq, shelving, tilting an a simple low/high cut block that I use in nearly every patch..

 

No longer do I fear dodgy room acoustics!

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43 minutes ago, Greg Edwards69 said:

Indeed.  This is one of the reasons that I bought the Helix.  It's worth the admission fee for the global eq section alone IMO. Okay, I might be exaggerating a little, but it's a 3 band fully parametric eq that includes hpf and lpf (labelled as low/high cut).  There's also a myriad of different eq block to use in presets, including a parametric that is the same as the global eq, graphic eq, shelving, tilting an a simple low/high cut block that I use in nearly every patch..

 

No longer do I fear dodgy room acoustics!

 

Oh absolutely! Helix is excellent for that and the built in global EQ / HPF is very welcome indeed. Brilliant piece of kit. 

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15 hours ago, chyc said:

Am I right in thinking that class d amplifiers get this HPF for free, or at least the amp's designers would need to explicitly build an amp to generate subsonic frequencies, which would make no sense?

 

 

No real sense in there.

 

ClassD amps routinely have a rumble filter. Some have an adjustable HPF.

 

Older style amps usually have a rumble filter.

 

If you left off filtering on a class D amp it would destroy speakers just as easily as an old one, or moreso with the gobs of power they tend to sport.

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On 15/09/2021 at 17:56, dannybuoy said:

Lots of amps have one built in anyway, but it’s not easy to discover which ones. I recall a thread on Talkbass with Agedhorse, a designer of Genz Benz amps talking along the lines that all their amps had such a filter but they never marketed the fact.

 

 

This nicely demonstrates what I've said elsewhere - that movement that you can see, you cant hear so its just wasted energy an wear and tear on your speakers. 

 

 

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Every bass amp has a first order high pass filter (6dB/octave) constituting its input capacitor (to block DC offsets) and input resistance, unless it has something more sophisticated built in.

 

Often the input resistance is high enough and the capacitor large enough for the corner frequency to be well below 30 Hz.

 

A thought out example might be 10,000 R and 1.0 uF giving 16 Hz.

 

My Laney Pro Bass has a first order LPF at 338 kHz  followed by an LPF at 6Hz. Clearly it's just intended to stop RF and DC inputs and have no impact on the audio frequency response. The frequency response is likely to be further limited by later sections of the amp, but clearly this design is vulnerable to'thump' saturating the preamp as a minimum.

 

A 'proper' HPF is usually at least second order (12bD/octave) so it can have a sharp 'knee' (-3dB) point as close to the lowest desired audio frequency as possible (which is more important than the steepness of the drop off, but they go together).

 

I can better appreciate the value of a variable HP filter after reading comments above. When compensating for room acoustics being able to vary the steepness as well as the cutoff point is clearly valuable as you may, for example, just want to control the deep bottom end, rather than eliminate it.

 

In the digital domain, virtually any filter behaviour can be modelled with little latency, which is, I suppose, why all in one pedals are so good at this.

 

 

 

 

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  • 3 weeks later...
On 22/09/2021 at 00:31, chyc said:

Am I right in thinking that class d amplifiers get this HPF for free, or at least the amp's designers would need to explicitly build an amp to generate subsonic frequencies, which would make no sense?

 

 

No, a class D amp can reproduce DC if the designer wished it to, just like a class AB amp. In fact a class D amp generally has higher performance at low frequencies.

 

The HPF has to be designed into the amp, the same as for any amp.

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