HPF curve shape
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LeeYoo
Well-known member
More info needed.
Speaker, preamp?
Frequency?
How sharp?
Speaker, preamp?
Frequency?
How sharp?
LeeYoo said:
passive
line level signal
100hz (doesnt have to be spot on)
almost like a wall, if possible, i like play around with its sharpness... as in waves Res_EQ plug_in HPF Q value,
it goes from mild shelving to almost brickwall
ruairioflaherty
Well-known member
penguin said:
You'll need an active filter to get the necessary steep slopes and there's no free lunch with filters, there are nearly always trade off between steepness of the filters and out of band anomalies (not to mention phase anomalies). There is tons of reading to be had on the subject all over the net.
Cheers,
Ruairi
ruairioflaherty
Well-known member
Time to get reading.....
This is one of the first links that comes to mind, there are hundreds of places to read up on this.
http://sound.westhost.com/articles/active-filters.htm#intro
Enjoy!
Ruairi
This is one of the first links that comes to mind, there are hundreds of places to read up on this.
http://sound.westhost.com/articles/active-filters.htm#intro
Enjoy!
Ruairi
Tekay
Well-known member
Neve's passive is 80Hz, "T" filter, 2 x 470nF and a 7H inductor. Use a 1k2 input resistor.
Samuel Groner
Well-known member
No, you can also design higher order passive filters with high Q. But you need inductors--not usually something which we want nowadays, particularly if they are above some uH.
For active filters I can recommend this online calculator:
http://www.beis.de/Elektronik/Filter/Filter.html
Samuel
sahib
Well-known member
penguin said:
Having a brickwall like response is hard enough with active techniques. You have to be really a hot filter designer to be able to do it passively. However, as Samuel pointed out you will need inductors to do it. You won't see very many examples of passive filter in that sort of response. I only remember one example in my IEEE transactions that I think gave 36dB but the inductor values are not something that you could find off the shelf. Unfortunately all of my books are boxed and stored at the moment. I'll have quick ramage to see if I can get to it. If I do I'll scan the schematic and post it.
I am sure when you read more about the filter theory you'll realise that 26dB slope not necessarily means a brick wall like response. You can have that easily by cascading four single pole RC network but with a very droopy result. The key is the mathematical relation between the poles.
> sharper cut for my passive HPF... passive - line level signal - 100hz - almost like a wall, if possible, i like play around with its sharpness
A simple R-C filter is 6dB/octave max, with a soft corner.
Cascaded R-C gets steeper way-down, but still a very soft corner.
We can bump the corner with amplifiers. That's cheating. It used to be expensive.
We can get "any" filter shape with passive components. Loudspeaker crossovers only skim the surface. There are fat books on the topic. Very steep filters need very many very good components.
How steep does audio really need? If your material is "normal/flat", anything over about 10dB/octave is not much more useful due to masking. OTOH, sometimes we have to take garbage. Truck rumble leaking through the walls, a bass-amp that booms 70Hz.
There is a class of "passive" passive filters which really depend on "excess amplification". Since amplification is now cheap, we often have <1K sources driving >10K loads, We can tap some of this "excess" to simplify filter design.
The choke will likely cost $10, and the cap close to a buck. Need two each. The chokes will want to suck all the hum in the room. The choke might distort, though the most available ones are OT and B+ filter units which won't be strained here. OTOH, a dual opamp is $0.50, resistors almost free, and active-filter caps can be scaled to dime-price.
A simple R-C filter is 6dB/octave max, with a soft corner.
Cascaded R-C gets steeper way-down, but still a very soft corner.
We can bump the corner with amplifiers. That's cheating. It used to be expensive.
We can get "any" filter shape with passive components. Loudspeaker crossovers only skim the surface. There are fat books on the topic. Very steep filters need very many very good components.
How steep does audio really need? If your material is "normal/flat", anything over about 10dB/octave is not much more useful due to masking. OTOH, sometimes we have to take garbage. Truck rumble leaking through the walls, a bass-amp that booms 70Hz.
There is a class of "passive" passive filters which really depend on "excess amplification". Since amplification is now cheap, we often have <1K sources driving >10K loads, We can tap some of this "excess" to simplify filter design.
The choke will likely cost $10, and the cap close to a buck. Need two each. The chokes will want to suck all the hum in the room. The choke might distort, though the most available ones are OT and B+ filter units which won't be strained here. OTOH, a dual opamp is $0.50, resistors almost free, and active-filter caps can be scaled to dime-price.
