pucho812
Well-known member
Which comes first hi or lo pass filters? Does it make a difference ?
Filter before eq? Does it make a difference?
Filter before eq? Does it make a difference?
My rule of (old) thump is (passive) LPF filter first to prevent slew overload...(rectification, RFI, etc).pucho812 said:Which comes first hi or lo pass filters? Does it make a difference ?
Filter before eq? Does it make a difference?
john12ax7 said:I would agree with pre-amp => filters => EQ. Not sure the order of hpf, lpf, and the EQ bands really matters all that much. Mostly it would just be dictated pcb layout and the order you want the front panel controls.
Indeed if mic preamps were linear up to light I wouldn't use a passive LPF in front of them.PRR said:In a true linear system, it does not matter.
or reduce gain, but if wind noise is a common problem and you can't use a wind screen on the mic by all means put your HPF early.If wind-rumble is overloading the system, you need to cut bass BEFORE it distorts something.
As I shared I prefer to set the audio bandpass HPF pole once with a high quality film cap... setting the other coupling caps in series octaves lower to be out of the way.Unless mad mosquitoes are swarming the mike, and your levels are too hot anyway, there is probably no rush to filter audio highs. (RF should be reduced ASAP.)
JohnRoberts said:Indeed if mic preamps were linear up to light I wouldn't use a passive LPF in front of them.
I did a lot of cascaded multistage active LPF back in my BBD delay line days.abbey road d enfer said:I would say it depends somewhat on the topology of said filters.
One very common issue with Sallen & Key variable HPF is the need for dual pots with one wafer being twice the value of the other. A common workaround consists in using a gain of about 4dB instead of unity to the voltage amp. Since this gain must be compensated for, it can be done before the filter, adding an attenuator and a voltage follower (S&K filter wants to be driven from low Z), which increases noise, or after the filter, which reduces headroom by 4dB.
I would say all sorts of permutations have been tried (some designers even advocate putting dynamics before the filters, which is silly IMO).
It seems some kind of consensus has been achieved with filters being before EQ, the order of filters making no significant difference in operation, as long as they are decently designed.
BTW I fully agree with JR's recommendation of preventing any VLF or VHF right from the start, using passive filters.
As a summing amp, it seems replacing R3 with an inductor may improve HF response and offer more gain margin. It's just a hint, but confirmed by simulation.JohnRoberts said:
I even played around with a variant on MFB topology to incorporate and use the natural bus capacitance of a long console bus run, putting that bus C in parallel with C2 using the above topology.
or the buggy whip....abbey road d enfer said:Purely speculative since analog summing improvements are akin to improving the petrol lamp or the pioneer cart.
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