HPF / LPF Questions.

[prkravi]

Hi All,

Pardon me if this is way too dumb to ask, im just getting my hands on a synth for the first time.

Was fidgetting with my M50 last night and i was wanting to try the effects of the Filters.
I'm in the First Prog - M50 Piano, I wanted to brighten up this Prog and make it more tangy and crisp.
By default it is assigned a LPF, so i go to page select intending to give it a bit more of High Frequency so that it becomes more sharp and crisp. And i change the Filter to HPF. But when i play...its barely audible...
I first thought it was probably because of my Interface - Presonus Audio Box USB. So i connected my M50 directly to my Monitors (Rokit 5) and still the same.

Questions:-
1. Is this intended behaviour of the Filter, i mean i thought it would let the HF pass through and it would be more sharper and brighter, but i can barely hear anything. As im typing this im thinking i should try once with my headphones to see if its the Monitor problem.

2. If a HPF makes the sound so feeble and completely inaudible, why and where do we use it?

3. While i was increasing the Vol on my Audio Box interface all the way, i realised that there was a strange HISS sound and beep noises as well. But this was not present when the M50 was hooked directly to my Monitors. What could be causing this? My laptop?

Thanks and sorry if they are too elementary....

[runeharpun]

It sounds like you don't use the filter as an effect (as IFX), but use the filter on the sound generator.

But even if you use one of the EQs or filter effect the HPF effect not very unusable in my opinion. I use the multimode filter, but the range for the filter makes it hard to get a good result. It should have been steeper, and also the frequency steps are too big.

R

[kimu]

a LPF is a low pass filter, it cuts all frequency above the so-called cut-off frequency. on korg (and others), cutoff is expressed as value from 1 to 127. In LPF, 1 means filter completely close while 127 means filter completely open (almost no high freqeuncy filtered out).

LPF (cutoff 1) |--not filtered-|..............sound filtered................ (hi frq)
LPF (cutoff 127) |------------not filtered----------|..sound filtered..

HPF (c.o. 1) ...filtered..|----------not filtered----------------------| (hi frq)
HPF (c.o.127) ..............filtered........................|-not filtered--| (hi frq)

on HPF is the contrary, 127 means filter completely close while 1 completely open, so it could be that moving filter to HPF you have just cutted away almost all audible frequencies on the patch, you should try to decrease cuto-off.

[EvilDragon]

1. Is this intended behaviour of the Filter, i mean i thought it would let the HF pass through and it would be more sharper and brighter, but i can barely hear anything. As im typing this im thinking i should try once with my headphones to see if its the Monitor problem.

This is the behaviour of the filter. If you have a cutoff point in the middle of the spectrum (say, at 2000 Hz), a lowpass filter will start gradually filtering from that point up to the end of hearable audio range (20000 Hz). On the same cutoff point, a highpass filter will start to gradually filter from that point DOWN to the end of the hearable audio range (20 Hz or so)... and piano sound is really based on low and mid frequencies... so that's why it thinned out for you.

2. If a HPF makes the sound so feeble and completely inaudible, why and where do we use it?

We use it to achieve different special effects... and to get rid of ultra-low frequency rumble when we don't need it. Highpassing a lot of sounds on 60-100 Hz cutoff point makes a lot sounds clearer and not muddy.

3. While i was increasing the Vol on my Audio Box interface all the way, i realised that there was a strange HISS sound and beep noises as well. But this was not present when the M50 was hooked directly to my Monitors. What could be causing this? My laptop?

Those are the high frequencies that the highpass filter let through. Yeah, they are silent somewhat, but they are THERE. This way you can see that there is not that much high frequency energy in the piano sound, it's all in the mids and lows.

on korg (and others), cutoff is expressed as value from 1 to 127.

On Kurzweil, cutoff frequency is expressed in ACTUAL pitch value, and can be fine tuneable in Hertz! This is the best way to do it, IMHO. Korg should implement it, too, on their next workstations!

I love being able to actually see WHERE is my parameter set up at. 1-127 doesn't help me at all for cutoff.

[runeharpun]

I think the filters (multimode IFX effect) have a fixed slope (6dB/oct I would guess). Of the 0 - 100 range of the frequency, only perhaps values 0 to 3 is below 100hz. So using the HPF for filtering out rumble with this kind of HPF is not an easy task. If the filters were steeper (18dB/oct), and also used logaritmic steps - then this HP filter would be far more usable. Perhaps using the mixers microphone hipass filters is a better option.

I guess it's a matter of taste and function, but having a HPF on some of the combis when playing along with a full band helps the sound a lot if the PA can handle low frequencies. Many of the preset sounds are already very bass heavy.

R

[prkravi]

Thanks guys all this is educative.
Why do i feel more like an Audio Engineer than a musician now?

Thanks again for all the inputs, i'll try out these later and ask more...

[runeharpun]

Why do i feel more like an Audio Engineer than a musician now?

As a start, make a combi from the patch you need (use the copy from patch function). Then insert the multimode filter in one of the vacant IFX slots. Use a HPF filter and set the frequency parameter to a low value. There are probably some resonance and other settings you need to tweak as well.

PM me with an email address, and I can send you one of my piano combis where I''m using a hipass filter.

R