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Help/Tutorial needed for using MC 19's Parametric EQ

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JimH:
Thanks, mwillems!

Arindelle:
Great post mwillems !

Now I know who to bother about how to use PEQ with existing active analogue crossovers  :P

mwillems:

--- Quote from: Arindelle on December 01, 2013, 09:00:54 am ---Great post mwillems !

Now I know who to bother about how to use PEQ with existing active analogue crossovers  :P

--- End quote ---

Anytime   :)  

I finished building a pair of home-designed bi-amped speakers about a year ago and after a brief attempt to use an active crossover in a box (a Behringer CX3400), I decided to try and switch to an all digital crossover in JRiver.  Because a good friend of mine and I were designing the speakers ourselves, there was no "right answer" about the crossover and EQ settings.  We had some basic ideas based on speaker design theory and the specs of the drivers, etc. but to some extent we just had to try things and find out what worked.  So I used JRiver and measurement software to tune the speakers, and in the process learned an awful lot about the PEQ module ;D

It's an unusual use case, but it's one area in which JRiver's PEQ really excels.  In normal analog crossover design (passive or active) you have simulation software, of course, but ultimately the only way to find out what's going to happen in practice is to build the circuit and measure the speaker.  Changing things at that point can be difficult and/or expensive (parts cost something).  It can be time-consuming and very frustrating for a hobbyist.  

By contrast, in JRiver, you click two times and it's different (two seconds later and for free).  If I were ever building another speaker with an analog crossover, I would probably wire up the drivers bi-amped first and use JRiver to simulate different crossover designs until I found one that worked, and then build that one.  It would take a lot of the guesswork out of the process.

VerySad:

--- Quote from: mwillems on November 28, 2013, 10:48:43 pm ---I think crisnee's suggestion is a good one, it can be hard to understand the filters in the abstract, and working with a GUI based parametric equalizer is a great way to get started. 

It might also help if you could explain what kind of EQ you want to do; we could help point you in the right direction.  Meanwhile, here's a brief explanation of what some of the more commonly used filters do (just be aware that many of them are actually more complicated/flexible than these descriptions would suggest).  Most of the EQ you'd want to do on a pair of headphones will be one of the first two filters described below:

Adjust a Frequency allows you to boost or cut frequencies in a certain frequency band.  The boost or cut will be bell-shaped; I attached a screen shot below illustrating what I mean by bell-shaped.  The frequency setting determines where the center (top) of the bell will be. The Q setting determines how wide the bell will be (lower Q means wider bell, higher Q means narrower bell): e.g. 1.4 Q is about one octave wide when the gain is 3dB (or -3dB); .66 Q is about two octaves wide with the same gain (the actual range of frequencies that is meaningfully affected will change depending on the gain setting, but this gives you a general idea).  The gain setting is how much boost or cut there will be at the top (or bottom) of the bell.  The channel setting lets you specify which channels are affected.  The screen shot below shows a 6dB boost at 500Hz with a Q of 2.

A High-Shelf allows you to boost or cut all frequencies that are higher than a certain frequency.  The boost or cut will increase as the frequency increases at different rates depending on the Q (higher is steeper, lower is more gradual).  The gain setting is how much total boost (or cut) there will be at the top (or bottom) of the shelf.  The frequency is the exact middle of the shelf's rise or fall.  The channel setting lets you specify which channels are affected.  A Low-Shelf is the opposite of a High-shelf, it boosts or cuts all frequencies below a certain frequency.  Here's a picture illustrating the response of two different shelving filters http://en.wikipedia.org/wiki/File:Shelving-eq.svg.  I don't know the exact parameters they used to create those examples, but the red trace in the illustration is probably a -3dB low shelf set at 150Hz with a Q of .5.

A High Pass Filter attenuates all frequencies below the set frequency by a continuously increasing amount (as frequency decreases).  The slope is the steepness of that attenuation (6dB per octave, 12 dB per octave, etc.).  A Low Pass Filter is the exact opposite, it attenuates all frequencies above the set frequency.  Here's an illustration of five different butterworth low-pass filters with different slopes (6dB, 12dB, 18dB, 24dB, 30dB) http://en.wikipedia.org/wiki/File:Butterworth_Filter_Orders.svg.  The 6dB, 12dB, and 24dB filters in JRiver should look exactly like the illustrated ones (1,2, and 4).  Correct use of low pass and high pass filters is kind of complicated, but they are typically used to create speaker crossovers, for protection of vented (ported) loudspeakers, or to interface a subwoofer with existing speakers. 

Adjust Volume lets you adjust the volume (up or down) of an entire channel by the amount set in the Gain parameter.  This is useful if you, for example, have multiple speakers of different varieties in a surround setup and you need to level match them; the Room Correction DSP module also has level matching tools. 

Delay lets you delay channels so that they output later than other channels.  This is useful if you have multiple speakers that are different distances from you, or if you're using an active crossover.  I'd recommend against setting delay in Parametric Equalizer unless you have a measuring microphone handy. The Room Correction DSP module also has tools to help address speakers that are different distances from you, and might be easier to use (without a mic) if you just need distance adjustment.

Reverse Polarity reverses the absolute polarity of the selected channel(s).  This is useful if your speakers are wired backwards, if you're using an active crossover, or for better subwoofer integration in some room setups.  The Room Correction DSP module also has an option to reverse polarity on a speaker by speaker basis.  More info about what "polarity" means in this context here: http://en.wikipedia.org/wiki/Absolute_phase#Sound_reproduction

Linkwitz Transform is a filter that boosts low bass performance of a speaker.  It is not typically a good idea to use a Linkwitz transform with vented speakers (speakers with ports in them), and isn't necessarily a good idea with sealed speakers (depending on your speakers and the settings you choose).  It's generally a more "advanced topic."  Here's a very good article on what it does with illustrations: http://sound.westhost.com/linkwitz-transform.htm

Limiters prevent sounds that are louder than the limit from playing on the selected channels.  They're essentially a method of protecting your speakers if you're concerned that they might get a damagingly loud signal sent to them.  This can usually be achieved in other, simpler ways (like turning down the volume on your amp), but there are circumstances where PEQ is the best place to handle that kind of thing. 

I hope that helps a bit. Let me know if you have questions about any of this, or any of the other filters.  Also, I hope other folks will feel free to chime in if I missed something.

--- End quote ---

I have a rather weird question. Does it matter if adjust volume is used before or after applying the filters?

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