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Frequency Response Graphs For Hd500 Eqs

hd500 eq frequency response graphs

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#1 pfsmith0

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Posted 08 May 2013 - 11:26 AM

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:

  1. An Audio Precision APx525 was used to generate the sound source and measure frequency response.
  2. Output = S/PDIF
  3. Input 1 = Mic. Input 2 = same. Mic level on back adjusted to give -20dBFS output with the Graphic EQ
  4. 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.
  5. There were no other FX or amps in the signal chain.
  6. 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.dropboxus...easurements.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 %).

Attached Files


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#2 silverhead

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Posted 08 May 2013 - 12:18 PM

Really useful stuff, pfsmith0. Thanks for sharing this.


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#3 meambobbo

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Posted 09 May 2013 - 06:05 PM

this is MOST excellent!  PLEASE let me add them to my site: foobazaar.com/podhd/toneGuide/

 

I have some data posted in the EQ section, as well as the link to Matt Mayfield's excellent video demonstrating the EQ's frequency responses, but these really help dial it home.


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#4 geppert

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Posted 09 May 2013 - 08:28 PM

Absolutely wonderful work and superb documentation. I downloaded the 160 meg Zip.

 

Thanks very much for doing this.


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#5 hurghanico

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Posted 10 May 2013 - 03:18 AM

thanks for sharing your findings


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#6 pfsmith0

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Posted 10 May 2013 - 11:30 AM

Certainly! Use this on your site as you see fit. If you have a more permanent place to store the files then I am interested in that as well!

 

this is MOST excellent!  PLEASE let me add them to my site: foobazaar.com/podhd/toneGuide/

 

I have some data posted in the EQ section, as well as the link to Matt Mayfield's excellent video demonstrating the EQ's frequency responses, but these really help dial it home.


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#7 meambobbo

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Posted 10 May 2013 - 06:40 PM

Certainly! Use this on your site as you see fit. If you have a more permanent place to store the files then I am interested in that as well!

 

Thanks so much! Trust me your work will get lots of visibility this way, and the files will be free to access over the web wherever you are whenever you like.


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#8 meambobbo

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Posted 10 May 2013 - 08:19 PM

all right - pictures are up!  i linked to this thread and gave you props.  let me know if you want me to include anything else.

 

http://foobazaar.com...uide/eq#effects


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#9 meambobbo

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Posted 10 May 2013 - 08:39 PM

absolutely bizarre about the shift EQ output - I'm going to experiment with that myself.  I want to post Ch. 1 as well, but I want to figure out which one is L and R.


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#10 pfsmith0

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Posted 11 May 2013 - 05:41 AM

Nice write-up meambobbo. I did not realize I maybe should have included the Q-filter. If/when I get the unit back into the lab I'll measure that as well - and determine which channel (left/right) has the messed up 4-band shift EQ high freq response. Also, please note that the Excel data file has the parametric peak frequencies for 1% adjustments. The graphs only show 5% so you may want to download the whole zip file from the link in the first post and include a 1% table in your write-up. I can't attach it here due to size constraints.


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#11 Astaroth_CY

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Posted 11 May 2013 - 07:28 AM

Excellent work. Line 6 should be paying you and the other people doing research on their machine.


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#12 snhirsch

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Posted 11 May 2013 - 03:04 PM

Thanks for all the good work.  It's a very odd marketing decision for Line-6 not to a) label effects parameters in terms of frequency and b)not make a family of graphs part of the technical documentation.  I don't think they're giving their customer base enough credit.  There may be a few folks who don't care about the details, but many of us do.


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#13 snhirsch

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Posted 12 May 2013 - 06:35 AM

I did a  PDF compilation of the graphs in a 2-up arrangement suitable for printing.  Unfortunately, it's too big to upload as an attachment.  If anyone wants to host it, let me know where to upload?

 

 


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#14 Astaroth_CY

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Posted 12 May 2013 - 06:41 AM

You can put it up on Dropbox and share it. You get 2GB of cloud space free.


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#15 pfsmith0

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Posted 12 May 2013 - 09:08 AM

I don't disagree with you, but I do see an advantage for using % instead of absolute numbers. With % they can always update or fine tune the frequencies to make them more useful thru future software updates. That being said, I don't find % very useful, although they're better than nothing. The whole reason I started this work was because I DIDN'T fine % useful. I needed the absolute frequencies so I could 1) understand what they do and 2) use them in a more direct manner instead of experimenting around (too time-consuming). But, I'm glad you're finding these graphs as useful as I do.

 

 

Thanks for all the good work.  It's a very odd marketing decision for Line-6 not to a) label effects parameters in terms of frequency and b)not make a family of graphs part of the technical documentation.  I don't think they're giving their customer base enough credit.  There may be a few folks who don't care about the details, but many of us do.


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#16 meambobbo

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Posted 12 May 2013 - 08:05 PM

Nice write-up meambobbo. I did not realize I maybe should have included the Q-filter. If/when I get the unit back into the lab I'll measure that as well - and determine which channel (left/right) has the messed up 4-band shift EQ high freq response. Also, please note that the Excel data file has the parametric peak frequencies for 1% adjustments. The graphs only show 5% so you may want to download the whole zip file from the link in the first post and include a 1% table in your write-up. I can't attach it here due to size constraints.

 

I took one look at one of those spreadsheets and said, WHOA.  I simply don't have time to parse all that data.  I think the 5% increments are good enough for most people.  I've never heard a complaint for more precision - it just kind of helps to give you a better frame of reference than x %.  Keep in mind I made the tables a ways back.  They seem to agree with your data from a quick spot check, but there may be some divergence.  But I think everything is good enough to give people a close idea of what to expect, which is the main point.  I missed some of the finer details that you discovered with your more detailed analysis, like the boosts before dips with the Parametric high/low params, and the 2.2kHZ Graphic EQ.  Those can be bewildering if you don't know about them.

 

Q Filter is a strange beast.  The parameters interact with each other in unpredictable ways, particularly mix and gain.  If you ever do an analysis on them, you'll see exactly what a mean.  It's difficult to explain in words or to even predict.  But for the purpose of pre-EQ I use it for, it's not that pertinent.

 

Anyway, let me know if you want me to add anything or change anything.  Again, great work, and everyone appreciates it.


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#17 pfsmith0

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Posted 18 May 2013 - 10:34 AM

Please note that I attached frequency response graphs for the Q Filter in the first post of this thread. Also, I identified the Left channel as having the odd frequency response in the Hi Freq portion of the 4 Band Shift EQ. The giant ZIP file containing all the data has been updated with this new information and can still be found in the Dropbox link shown in the first post. Enjoy!


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#18 Ball_ed

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Posted 18 May 2013 - 04:54 PM

Great work, thanks for sharing bro...


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#19 Warfare

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Posted 19 May 2013 - 10:07 AM

Excellent work, thank you, I will take a deep look !


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#20 pfsmith0

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Posted 02 June 2013 - 05:01 PM

I attached a PDF file to the original post the lists the Frequency (in Hz) represented by Parametric EQ Freq (in %).


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