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In the process of trying to figure out what a 4 Band Shift EQ is, I put my HD500 on the test bench and measured the frequency response of ALL the EQs in the HD500. I thought you'd find it useful so I'm sharing the results here. For example, what does a 100% shift mean? What does 0% Q mean? And just where is Freq = 38% in the Parametric EQ? Did you know when you set 2.2kHz of the Graphic EQ to -12dB you'll get a +12dB boost (!) at 1kHz before it dips down at 2.2kHz? No wonder it didn't work very well to eliminate a pesky feedback problem, but caused another one instead. Using these can give you insight into which EQ you really want to use. I've attached the most pertinent pictures here (zipped together to make it easy). The only potential problem is the 4 Band Shift Hi Freq which has mismatched L/R channels (~3dB at 1kHz)! Every other EQ and every other setting has perfect L/R balance (less than .1dB mismatch) but this one does not. I've contacted Line 6 support before submitting this here but they see nothing out of the ordinary (i.e., it sounds fine, which may be true, but there's still a mismatch, big enough to be called a bug in my opinion). I've labeled those two graphs channel 1 & 2 because that's what my test equipment calls them. Unfortunately I didn't have the forsight to find out which was left and which was right before I tore down the setup. But the fact of a mismatch remains. Some things you need to know to properly interpret these: An Audio Precision APx525 was used to generate the sound source and measure frequency response. Output = S/PDIF Input 1 = Mic. Input 2 = same. Mic level on back adjusted to give -20dBFS output with the Graphic EQ Unless otherwise indicated, the gain of all the other EQs were set to nominally give -20dBFS. The gains were recorded so you can see which EQs have built-in gain or loss compared to the Graphic EQ. There were no other FX or amps in the signal chain. Sample rate = 44.1kHz (factory default) I have more complete files that contain the actual data (not just pictures) as well as more settings than shown in these few pictures attached here. Until I can find a better place to put it, you can download the entire 160M set of Excel files from: https://dl.dropboxusercontent.com/u/56306778/HD500%20Measurements.zip. I am open to ideas of where to put this on a more permanent basis. Enjoy! I hope you find these as useful as I have. ---------------------------- I took the HD500 back into the lab and verified that it's the Left Channel that has the odd frequency response in the Hi Freq portion of the 4 Band Shift EQ. I re-uploaded the Excel files to indicate this and re-uploaded the new 4 Band Shift EQ figures here. ---------------------------- I measured the frequency response of the Q Filter (per meambobbo's post) and attached it here. I also updated the giant zip of Excel files. I think this could emulate a pretty Morley wah if you make toe = hi Freq/hi Q/hi Gain and heel = low Freq/low Q/ low Gain. Also, mix attempts to add the filtered signal to the straight signal, which it does. But the filtered signal has some processing delay so the mix includes some notches in the 4k-8kHz region you may not be expecting. You can see this in the attached graphs. For the signal levels I was using (-20dBFS thru the Graphic Equalizer) you can also see some gain compression with the Q filter. So if you want it clean, stick to the lower Gain levels. ----------------------------- Added a PDF file that lists the frequencies (in Hz) represented by the Parametric Frequency (in %). Updated links to ALL my measurement files: Amp Frequency Response Pre and Full (Excel) Cab DEP Parameters (Excel) Cabs with 121 Ribbon (Excel) Gains (Excel) Mic Frequency Response (Excel) Amp Tone Controls (pdf) Amp-Pre Frequency Response (pdf) Cab Frequency Response (pdf) FX Gain (pdf) Model Pak Frequency Response (pdf) Global EQ (zip) Huge 185M EQ frequency response file (zip) This last one was the original subject matter of this thread.