Low Cut

diminu · Post by **diminu** » Wed Feb 13, 2008 4:59 am

Is there any Low cut available for Scope which really cuts ( not only atenuates) the frenquencies lower than 30-40 Hz. or above 18 KHz ? I know the UAD Cambridge is able to do this. But ...
greetz
diminu

chriskorff · Post by **chriskorff** » Wed Feb 13, 2008 9:26 am

The frequency that you set the low/high cut filters to work at is (I think) the frequency at which they <i>begin</i> to cut, and above/below that frequency they will attenuate at whatever dB/octave slope you've chosen (24dB Octave means that, at one octave below the frequency you set the low-cut filter to, the sound will be attenuated 24dB).

It sounds like you're after a steeper slope — I think PEQ4 has a 48dB/octave filter (I'd need to check though). I'm certain the STM mixers have 48dB/octave filters though, as I was using them the other day.

Perhaps there's a freebie on devices that goes steeper than that? There are problems with steep filters though, such as ringing, phase problems and time-shifting at various frequencies (I'm no expert, but I think these are some of the reasons why infinity dB/octave filters, such as the one you seem to be describing, don't exist).

Cheers,

Chris

Shroomz~> · Post by **Shroomz~>** » Wed Feb 13, 2008 11:40 am

I made an experimental 72dB stereo EQ that you can try. The configuration is stereo input amp > 72dB High Pass EQ > 72dB Low Pass EQ in series giving you extreme Low & High cut capabilities in one compact stereo insert effect.

http://www.planetz.com/forums/viewtopic.php?t=24399

Please feel free to try it & test it & let me know what you think.

Shroomz~> · Post by **Shroomz~>** » Wed Feb 13, 2008 11:41 am

Aww, Stardust beat me to it while I was typing.

diminu · Post by **diminu** » Wed Feb 13, 2008 1:17 pm

Hi all,
i´ve tried all your suggestions but the resulting effects are all nearly all the same. The biggest attenuation is at around -30dB shown by wolf´`s spectrum analyzer.

Thank you for the effort.
diminu

Shayne White · Post by **Shayne White** » Wed Feb 13, 2008 1:36 pm

The Sonic Timeworks VintagEQ bundle has a 36db/octave highpass filter in it. I use it all the time, and it works and sounds great.

Shayne

chriskorff · Post by **chriskorff** » Wed Feb 13, 2008 2:27 pm

Hi Diminu,

Can I ask if there's a specific, practical reason for you needing to have absolutely zero content below 40Hz? The only other way to achieve this, beyond a practically impossible-to-implement brickwall filter at 40Hz, would be to choose a very shallow filter (so as not to attenuate too much <i>above</i> 40Hz), set significantly higher than 40Hz, which attenuates at such a rate that by the time it goes as low as 40Hz, it's working below the noise floor of your DA converters.

Of course, if it's just a musical result that you're trying to achieve, you're better off using your ears than a spectrum analyzer.

Cheers,

Chris

Shroomz~> · Post by **Shroomz~>** » Wed Feb 13, 2008 2:59 pm

No worries Stardust. If you're not fast you're last as they say.

diminu wrote:i´ve tried all your suggestions but the resulting effects are all nearly all the same.

You should be getting 72 dB/octave out of the device I posted tonight. (take the link in my post above)

The biggest attenuation is at around -30dB shown by wolf´`s spectrum analyzer.

diminu, you absolutely need to test such devices with an FFT spectrum analyzer & preferably with a single white noise source (control room test gen' for example) fed to both left & right channels. I only recommended that you do so before using it seriously on any work, because such an EQ definitely has different characteristics which might be unwanted on certain material. If needed, I can post screenshots from the analyzer we use here that show 72dB of low & high cut achieved with the EQ I posted, but any of you can verify that with your own tests if you want. Admittedly, 72dB is really exrtreme, but It would also be possible to add the required switching to allow 36/72 dB/octave toggling or it could even be made 24/36/48/60/72 switchable.

Post by **hubird** » Wed Feb 13, 2008 4:42 pm

as suggested by criskorff already, besides other unwanted effects in phase you'll get a peak at the cutoff fr. of several dB, up to 6 or so.
I wouldn't try to cut at 72 dB, musically.

Shroomz~> · Post by **Shroomz~>** » Wed Feb 13, 2008 9:33 pm

hubird wrote:besides other unwanted effects in phase you'll get a peak at the cutoff fr. of several dB, up to 6 or so.

There's no nasty peak at or around the cutoff frequency with the 72dB EQ I posted, either on the low or on the high cut. There's certainly some issues with such a steep filter/EQ which do give it some slight peculiarities, but it's definitely not beyond being usable if you wanted something so severe, especially for extreme spot FX or for certain types of electronic music). Test it yourself or even just play around with it on some material & then make your mind up. One of the main issues I've noticed is that it's not giving as much as a 72dB low cut, more like 60dB or so with white noise tests, but that's still more than enough I think. The high cut however, is definitely giving the 72dB cut & again, without any nasty peak or peaks. I'll post a couple of FFT analyzer screenshots in the devices forum.

sonolive · Post by **sonolive** » Fri Feb 15, 2008 2:13 am

hi diminu,

You will probably need a FIR FFT Filter ... that can effectively give you a -74 dB attenuation with linear phase, such a "mastering filter" is on fire here at DAS and probably released "soon"

you got to be patient !

cheers
olive

dawman · Post by **dawman** » Fri Feb 15, 2008 4:13 am

Tandis que nous sommes jeunes ! !

diminu · Post by **diminu** » Fri Feb 15, 2008 4:43 am

Hi chriskorff,
You asked for the practical reason to low cut so heavy. To be honest, I´m not sure if is necessary, because you hardly can´t hear sounds lower than 30 Hz as you surely all know. I just want to be sure, that they are completely gone and cannot influence for instance a compressor.

Hi Shroomz.
I don´t have that special FFT analyzer. It is possible, that the spectrum analyzer is not as reliable as necessary. Are there analyzers available for scope?

Hi sonolive,
good news.

To all,
I must confess not being an expert in such things. However the great resonation on this thread indicates a general interest in this topic.
Thanks to all.

diminu

Shroomz~> · Post by **Shroomz~>** » Fri Feb 15, 2008 5:30 am

Hi Diminu, try Visual Analyser by sillanumsoft. It's free & is working very well here.

wolf · Post by **wolf** » Sun Feb 17, 2008 1:40 pm

chriskorff wrote:The frequency that you set the low/high cut filters to work at is (I think) the frequency at which they begin to cut

no .. not really: the cutoff frequency is usually the area where the signal is already dampened by 3 dB.

Shroomz wrote:you absolutely need to test such devices with an FFT spectrum analyzer

Why ? A cut below i.e. 100Hz should be shown on both, shouldn't it.

diminu wrote:I don´t have that special FFT analyzer. It is possible, that the spectrum analyzer is not as reliable as necessary.

no, they are just different ways of measuring.
For me the musical presentation of a band based analyzer is much more helpful for mixing than fft based analyzers.

diminu wrote:To be honest, I´m not sure if is necessary, because you hardly can´t hear sounds lower than 30 Hz as you surely all know.

Most (pro) studio speaker systems don't even go below 50Hz.
But even then I just can give you one tip regarding the control of lows:
learn your speakers (i.e. how they translate onto other systems) before adjusting something you only can see.

I just want to be sure, that they are completely gone and cannot influence for instance a compressor.

uhm, well .. especially a compressor can give great control about lows. I.e. lows for kicks usually come later .. just set the attack time of the comp to compress, when the lows come in.
You could also set up a filtered sidechain to only control compressing in a special frequency area. And/or use another comp before - again sidechain filtered but this time via a high cut -> compressing all below the given freq. away.
Far better then the brute force method via a hard cut filter.

cheers,
Wolfgang

Shroomz~> · Post by **Shroomz~>** » Sun Feb 17, 2008 2:55 pm

wolf wrote:
Shroomz wrote:you absolutely need to test such devices with an FFT spectrum analyzer
Why ? A cut below i.e. 100Hz should be shown on both, shouldn't it.

Hi Wolf, I'd really rather not have got into this, but since you're promting me, I wasn't suggesting that your spectrum analyser isn't a usefull tool, because I think it's pretty cool, but it's certainly not the type of device I'd suggest to someone for testing devices and their frequency responses as opposed to using an FFT based analyser. The band based approach just isn't going to give accurate enough information.