Wotcha.

I've been playing with the Equaliser on my Mark 2 for about 6 months now, and keep getting to a point where I feel its tweaked to perfection, then just for a laugh I change to a flat preset and it suddenly sounds much better. But not quite perfect, so I tweak some more and it almost gets there, then back to flat again etc. etc. etc....

Is there some form of scientific approach to take with getting the equaliser settings to sound nice? Does anybody have a nice simple to understand explanation of how the various Q values and frequency steps interrelate?

I've come to the conclusion that all I need to do is frig the equaliser to provide a 40-50Hz high pass for the front channel (which powers the factory fit speakers) and a 100-200Hz low pass for the rear channel (powers a sealed 12" sub).

I've searched other threads on this matter - Tony mentioned that he'd tried this and it's not the best plan in the world, and that using external X-overs is a better approach. But surely the mighty morphin power DSP in the empeg could do this?

I've been using the X-overs in the amps until now - the 4 channel amp for the factory speakers has switchable 80Hz lo/hi pass filters, but 80Hz is a bit too low for low pass, and a bit too high for high pass. On some tracks it sounds fine, but on others I just get muffled rumblings coming from the boot - it seems I'm missing a huge chunk of mid-bass. Then again if I switch off the hi-pass filters the poor factory fit speakers sound very muddy in the mid range, trying to cope with sub-bass they can't possibly hope to reproduce. It's a company car so fitting new speakers isn't really an option, and I really can't face ripping the dash apart all over again and forking out for external X-overs.

Anybody have any ideas? Do I need to bite the bullet and buy yet more audio kit? Does anybody understand how equalisers work?

Cheers guys,

Andrew.

There is RTA, or RealTime Analysis. I've done it, and it works, but it's a pain in the you-know-what. It involves using a PC with spectrum analysis software, combined with a calibrated microphone and test tones, to get rid of any nasty peaks and valleys in your spectrum.

Now, something to keep in mind. If you're running version 2.0 beta 11, and you've been playing with the Q values, you must understand that custom Q values are only working for one channel. The other channel is getting a Q of zero. This is a known bug in 2.0 beta 11.

This might account for some of your reported behavior.

If you want to work around this bug, either set the Q value independently for left channel and right channel, use the automatic Q values, or downgrade to non-beta 1.03.

If you're looking for a treatise on what the Q actually does, click here.

Thanks for the FAQ link - very helpful.. However it talks about using high Q for a narrow curve, and low Q for a wide curve. Is there a mathematical formula that defines this more specifically?

Is there any kind of funky sotware available that will calculate these equaliser settings? Has anybody else managed to achieve low-pass or high-pass effects using the empeg DSP?

I've been thinking about RTA for a while but it does sound like an enormous faff. I've come to the conclusion that the normal speaker frequency response is good enough not to worry about too much, but I do need to get the x-over frequencies right to avoid getting distortion everywhere.

I didn't realise there was a bug with Q values not replicating across the channels - presumably this is fixed in beta 12? And how do I set the Q values back to automatic mode once I've been fiddling with them?

Thanks again....

IIRC, Q = Fc / (Fh - Fl), where Fc = sqrt(Fh * Fl)

Fc = Center frequency, Fl & Fh are the low and high limits of the band (-3dB points)

/Michael

Been thinking about this for a while....

Say I wanted a high pass cut off at 100Hz, say 3dB per octave. If I set -3dB at 50Hz, -6dB at 25Hz, -9dB at 12Hz, would this approximate to something like a high pass crossover curve? Am I right in thinking that a Q of 0.5 in each case would give roughly the right shape curve? It would be very lumpy but would have at least a downward trend and cut more bass with lower frequencies.

If I wanted a steeper curve (say 12dB per octave) would that work with cutoffs of -12dB, -24dB, -36dB, but with a Q of 2.0? Is there a mathematical formula that defines the shape of the parametric curve? I'd like to plot these curves graphically, then compute the sum effect of each equalisation step to derive the overall effect. Anybody know of any good (free) software that would allow this kind of graphing?

Alternatively, maybe this could be handled in the digital domain instead? The Auto volume thingy in hijack analyses the outgoing sound data stream and tweaks it to apply a multiplier before it reaches the DSP. Could the same approach be applied to create a low/hi pass filter effect? Hmmm... maybe this would only be in stereo so I don't think it would solve my problem...

My brain hurts now, so I might just go and buy a variable high pass filter instead. Sigh.

Someone else played with trying to do a filter (don't recall if it was HP or LP) but it's just not meant to be a filter with infinite damping below or above a certain frequency, just to nudge the curve up or down at certain spots. You might be able to get something passable, but you'd be far better off with an external (or incorporated in the amp) filter...

/Michael

Has anybody else managed to achieve low-pass or high-pass effects using the empeg DSP?

Do NOT use the equalizer as a high pass filter or a low pass filter. It is not a useful substitute for a proper crossover circuit. It does not work well at all when you try to do this. It only attenuates to a degree, it does not do a complete shelving cutoff.

If you need a proper crossover, use a proper crossover. Most amplifiers have proper crossovers built-in.

I'll add this information to the FAQ entry.

Well, just to be contrary I'm gonna give it a go anyway. Worst case scenario is it sounds pants and I'll buy a high pass crossover. I wish I'd got a 4 channel amp with variable crossover points now, instead of just fixed 80Hz points. The bass amp has a crossover which varies between 20 and 250Hz, but it's never really seemed that impressive...

I'll let you know if I get any joy with this.

Cheers.

Andrew

Okay, don't listen to me. That's fine, it's within your rights.

Right then. I've been dabbling with my eq settings for a while now, and got things to sound ~reasonable~ but I'll concede that I do indeed need to use active crossovers to achieve this.

So, yep, you were right and I was wrong :-)

For the time being, I'll be keeping the equaliser settings to try and cut some of the low freq stuff from my front speakers.

During my playing, I've noticed some very odd behaviour; I have a 4 channel eq profile, with the front 2 channels all flat except a -30db cut at 18Hz, with Q of 24. The rear 2 channels are flat except a -4db cut at 40Hz, using default Q values. This gives approximately the right audio effect I'm after, but:

If I switch between this eq. profile and the default flat profile whilst playing any music the sound output completely cuts out! When I first tried this I thought I'd killed the empeg or my amps, but switching the player off and on again makes it then work with either eq profile. If I pause playback and then swap eq's, I can resume playback and it works fine with the new eq. setting. This is really weird - I presume there's some kind of limitation with the DSP that doesn't like extreme changes being applied during playback?

I've not yet tried this with the new beta13, so not sure if it's a known bug. There seem to be some issues with empacman working on beta 13, so I'll be waiting a few days before I do this upgrade.

It would be good if somebody else could confirm this odd behaviour on their player? Or am I just going mad?