Simple Shelving EQ

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Stonerbox

Member
Joined
Jan 13, 2014
Messages
6
Hai!

I mostly hang around over at the DIYStompboxes forum but for this one I need to enter the holy realm and magical grounds of GroupDIY.

I countered a problem recently. I cannot insert hardware into my interface without the minimum of 14ms latency, and that does not work very well when you need to treat a signal in real time and be able to hear it in the cue/headphones. I want to treat a mic that needs a little shelving push (5-8dbs) at 100-150hz and 10khz.

I sketched up a very basic idea for this but I need some help on which EQ (no inductors, transformers or +100vcc) I should go with? Would the Poor Man's Pultec EQP1-A be a good choice perhaps? Let me know what you think!

Link to full sized image : http://i.imgur.com/AHYA6G3.png
Link to alternate color scheme (easier on the eyes) :http://i.imgur.com/i8jOezX.png
MFkMiu5.png

 
What about audiox's studer, there is a 500 version with mid peak/dip and a mastering version. For any you could pick the freqs you want, there is info on how to do it. Well documented project and very simple.

http://groupdiy.com/index.php?topic=36522.0

JS
 
If you want something simple and cheap that will work on your 9-18V then a Baxandall topology might work well here. There is even an equation for working out your shelving frequencies here:

http://sound.westhost.com/dwopa2.htm

I must say I am confused by the picture you attached though. Does it go:
A) Mic-->Preamp--->EQ--->Interface
B) Mic-->EQ--->Interface

If it's B then you will need to build a mic preamp before the interface as well. There are difficulties in designing a high quality preamp without either an input transformer or bipolar power supply. Also if you are using a condenser mic then you will need to build a 48V supply anyways.

Can you tell us what kind of interface you are using as well?
 
I don't know if it is my laptop display or just my old eyes but I find it rather hard to see your diagram. Exactly where in the signal chain are you suggesting placing this EQ? Do you have a mic pre? The PMEQP1A might be overkill for your needs.

Cheers

Ian
 
joaquins said:
What about audiox's studer, there is a 500 version with mid peak/dip and a mastering version. For any you could pick the freqs you want, there is info on how to do it. Well documented project and very simple.

http://groupdiy.com/index.php?topic=36522.0

JS

Thank you JS! I'll check the audiox studer out. (edit):Unfortunately it needs  a transformer, but I guess I could order one. I'm probably looking for something less complicated and less expensive. Looks like a awesome build though!

electric_diaries said:
If you want something simple and cheap that will work on your 9-18V then a Baxandall topology might work well here. There is even an equation for working out your shelving frequencies here:

http://sound.westhost.com/dwopa2.htm

I must say I am confused by the picture you attached though. Does it go:
A) Mic-->Preamp--->EQ--->Interface
B) Mic-->EQ--->Interface

If it's B then you will need to build a mic preamp before the interface as well. There are difficulties in designing a high quality preamp without either an input transformer or bipolar power supply. Also if you are using a condenser mic then you will need to build a 48V supply anyways.

Can you tell us what kind of interface you are using as well?

I've been thinking about that one, but some one over at Gearslutz (of course) said it would not work very well in these kind of situations, Impedance-vise, but there is nothing a buffer can't fix right?

The layout is a bit confusing now that I think about it, I'm gonna update it. Anyways it goes like this!
[Mic -> EQ -> Preamp (integrated in the interface) -> Converters -> and so on.. ] I hope that cleared out any confusion.

ruffrecords said:
I don't know if it is my laptop display or just my old eyes but I find it rather hard to see your diagram. Exactly where in the signal chain are you suggesting placing this EQ? Do you have a mic pre? The PMEQP1A might be overkill for your needs.

Cheers

Ian

Hi Ian,

Yeah, when I was making the sketch I was a little bit concerned that it was too dark. I'm gonna go ahead and do some color adjustments. :)  BTW, you can always check the link to the full sized image (above the thumbnail).
 
Stonerbox said:
joaquins said:
What about audiox's studer, there is a 500 version with mid peak/dip and a mastering version. For any you could pick the freqs you want, there is info on how to do it. Well documented project and very simple.

http://groupdiy.com/index.php?topic=36522.0

JS

Thank you JS! I'll check the audiox studer out. (edit):Unfortunately it needs  a transformer, but I guess I could order one. I'm probably looking for something less complicated and less expensive. Looks like a awesome build though!
...
The layout is a bit confusing now that I think about it, I'm gonna update it. Anyways it goes like this!
[Mic -> EQ -> Preamp (integrated in the interface) -> Converters -> and so on.. ] I hope that cleared out any confusion.
...

Two things here, the studer doesN'T NEED a transformer, there is an option you could replace with an electronic input which is an option already on the board IIRC.

Second, having the preamp after the EQ is really a bad idea, noise will bi an issue, no doubt. What you could add but still not the best idea is a filter, so you get some attenuation in the mids at mic level, you should check on your DAW what shaping you want and design a passive filter for that but is rather hard or impossible to archive the impedance matching you need for best noise performance, you probably loose some N/S ratio but less than with an active eq in the middle. The optimal option is to add an external mic pre, then a line level eq and then go to the converters at line level. A mic pre with integrated EQ would be your best bet here if you want to maintain the noise low.

JS
 
joaquins said:
Two things here, the studer doesN'T NEED a transformer, there is an option you could replace with an electronic input which is an option already on the board IIRC.

Second, having the preamp after the EQ is really a bad idea, noise will bi an issue, no doubt. What you could add but still not the best idea is a filter, so you get some attenuation in the mids at mic level, you should check on your DAW what shaping you want and design a passive filter for that but is rather hard or impossible to archive the impedance matching you need for best noise performance, you probably loose some N/S ratio but less than with an active eq in the middle. The optimal option is to add an external mic pre, then a line level eq and then go to the converters at line level. A mic pre with integrated EQ would be your best bet here if you want to maintain the noise low.

JS

I did not realize you could build it without the transformer, that's good to know in the future!

The noise is a trouble.. That's unfortunate. I realize more and more that I should have thought about the hardware-side of things before I decided to buy this interface. Don't get me wrong 'cause I love my SPL Crimson, best preamps and converters I ever had but when it comes to inserting hardware eq, compressors, delays and such I'm  somewhat.. limited. Crap.
 
Stonerbox said:
The noise is a trouble.. That's unfortunate. I realize more and more that I should have thought about the hardware-side of things before I decided to buy this interface. Don't get me wrong 'cause I love my SPL Crimson, best preamps and converters I ever had but when it comes to inserting hardware eq, compressors, delays and such I'm  somewhat.. limited. Crap.

Does it have a line input as well as a mic input?

Cheers

Ian
 
Unfortunately you have a decent channel strip but you have no choice but to use its on board effects. There is no way to bypass the mic pre as it has no line in.
Im not saying you should sell it but if you want other outboard gear you're gonna have to use another converter.
 
> rather hard to see your diagram

I prefer a simple burnt-stick on light papyrus. Colors and wide range of text sizes are challenging.

I still do not know what it says. Or why it was so big.
 

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PRR said:
> rather hard to see your diagram

I prefer a simple burnt-stick on light papyrus. Colors and wide range of text sizes are challenging.

I still do not know what it says. Or why it was so big.

Man, do you ever have anything else to add than sarcasm in threads? I'm getting sick of your insecure ways of pushing people. Do you have issues with the world around you or what? Weak.

Edit: Oh by the way PRR. You f**ked up the ground.
 
It does have line input, actually four of them in the back.

ruffrecords said:
Does it have a line input as well as a mic input?
Cheers

Ian

yep, I figured that much too. Damn shame! But lesson learned til' next time.

Rocinante said:
Unfortunately you have a decent channel strip but you have no choice but to use its on board effects. There is no way to bypass the mic pre as it has no line in.
Im not saying you should sell it but if you want other outboard gear you're gonna have to use another converter.
 
ruffrecords said:
In which case you can build a mic pre with built in EQ and feed its output into your interface line in.

Cheers

Ian

That is actually one way to do it, good idea! I could build a preamp with a little bit of color (perhaps a neve-style one) as a complement to my other preamps.
 
I was wrong and confused the Crimson with something else.  It bypasses the mic preamp when line in.  My apologies and oops.  I'll shut up now.
 
Stonerbox said:
PRR said:
> rather hard to see your diagram

I prefer a simple burnt-stick on light papyrus. Colors and wide range of text sizes are challenging.

I still do not know what it says. Or why it was so big.

Man, do you ever have anything else to add than sarcasm in threads? I'm getting sick of your insecure ways of pushing people. Do you have issues with the world around you or what? Weak.

Edit: Oh by the way PRR. You f**ked up the ground.

As a newbie let me help you a little.  I've been here maybe 10 years there is an incredible amount of smart and generous people on this forum, it's kind of amazing.  I'm pretty sure that not one person will disagree with me when I say PRR is the most treasured member here.  He has answered thousands of questions for new and old members, for those who did their homework and those who did not.

I'd ask that you try to learn the way this forum works before taking it for granted.

Welcome to the forum

 
And yes, you should build a mic pre with eq and feed it into your line input, eqing a signal between mic and pre is hard to do with phantom going on.

An API style pre is super easy to build and sounds great, look at www.classicapi.com for nice parts and kits.  For the eq a simple Baxandall style would be great.  Do you have Douglas Self's book "Small Signal Audio Design"?  If not it's well worth picking up for the EQ section alone.
 
Stonerbox said:
PRR said:
> rather hard to see your diagram

I prefer a simple burnt-stick on light papyrus. Colors and wide range of text sizes are challenging.

I still do not know what it says. Or why it was so big.

Man, do you ever have anything else to add than sarcasm in threads? I'm getting sick of your insecure ways of pushing people. Do you have issues with the world around you or what? Weak.

Edit: Oh by the way PRR. You f**ked up the ground.

Hilarious, and note that PRR "liked" it!  I thought the OP was joking because he knew him...maybe not!?!
 
Stonerbox, about PRR comment, I try not to make judgements on any community before getting to know some about it. We do play our jokes, I hope your intention was that. PRR is a really good member but everybody takes a hit when drops something, pictures that are too big or hard to read are pretty common, I've seen pictures upside down! I never saw one of those break loose without any joke in the middle. Same thing happens when someone who knows better make a math mistake or basic physics, I've took my hits as what they are and I've also made some. I hope you are willing to take this as it is and enjoy the forum, lots of knowledge is shared here and is a great group of people to share it with.

There is a known joke online about this...

Ah, I was missing the point, for your problem, maybe an INA preamp or something simple like that followed by a simple EQ, maybe a baxandal, maybe something else, should work. INA or single IC preamp  projects are a lot around, same thing for EQ. Maybe you would like to look around for some META or make a search for this things.

JS
PS:I hope my attached picture comes good  :eek:
 

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