Dynamic Stereo EQ project, C4'ish

Hey to everyone!

Due to my Bachelor thesis I'm working on a Waves C4 kind of dynamic EQ, which I'd like to share with you. Also it would be nice to get a second opinion on everything, so you're kindly asked to critize the sh*t out of my schematics! ;D

But be warned: I don't study electronical engineering and have just little knowledge about electronics. So it might just be garbage... I always read your discussions on different topics from which I don't get half and it would be great, if you could give me some advice.  Here are some screenshots from eagle.

A pretty much standart debalancing Input section and an amplification circuit with gain=3 for three targets (VCA, SC, SC - Does gain make sense here?):


Then we got electronical crossovers. Now, the idea is to be able to turn one pot (just like in the C4 plugin) and change two filters: the high cut of the lower band and the low cut of the higher band. Of course, both have to cut within same frequency range.


After that there is the dynamics section. My idea is to use both Sidechain inputs on a That 2180 and to make one of the Sidechains starting points changeable. With that in mind, only the difference between the two Sidechain signals should lead to a dynamic change in gain at the 2180. Now, there are two obvious problems I'm facing:
1. The That 2252 was discontinued (I started in late november but didn't realize it until now )
2. In its datasheets it is not specified on how to change its input sensitivity. There is an example where it's configured for -10dBV, and so is it in my schematics, but I don't get where they got that from. Maybe I'm just a little too unexperienced or blind, but I'd really appreciate it if someone could help me with this! (I assumed it has to be the input resistor, but please, tell me if I'm wrong!)


Last but not least, there is a summing amp. I tried to find data about how to scale the summing resistors, but didn't succeed. Any advice? IC24 has already been kicked out.


I'm looking forward to hearing from you! Thanks to everyone in advance and to all the makers of this forum. It's a great community!

Börje

Huh? I am confused... Waves C4 is a multiband compressor... This post is in the dynamics processsors forum but your thread is talking about an EQ design????

Hi frazzman,

Sorry for the confusion! :-[

I posted this here, because it shall become a dynamic processor, but with an absolute term in its sidechain.

The C4 is kind of a mix between a multiband compressor and a dynamic EQ. Because of its non-overlapping frequency bands it seems like just a multiband compressor, but it allows you to determine the maximum compression or expansion in dB. That's a function that only applies on a dynamic EQ.
Now that I'm reading this, I realize how small the difference is and I hope that nothing gets lost in translation.  :-\

My idea for realizing the "limited compression/expansion" was to use two sidechain generators, one at the inverting, and one at the non-inverting control input of the VCA, so that they will cancel out. Then, by turning the "Range"-Pot (i.e. 0-20dB), I want one of the sidechains to change its starting point/behaviour, so that the sidechains are unbalanced and compression or expansion starts.

Best regards ,

Börje

your referring to doing something like the bss dpr901

It's a very useful tool....

Here is a description of the DPR 901 II from the BSS website:

DPR-901II Dynamic Equaliser

The DPR-901 II is a four-band parametric Dynamic Equaliser which allows frequency-selective compression (-3OdB) and expansion (+16dB).

Each band has:

A frequency sweep.
A bell width.
An IN/OUT switch.
Compress/expand control.
Compress/expand metering.
Threshold metering.
Time constants which are automatically controlled by dynamic and harmonic content of signal with selectable FAST RELEASE.

It has a filter switch on bands 1&4 which changes bell filter response to a shelving response and on bands 2 & 3 cancels the filter for wide band operation.

Electronically balanced input and output.

The unit may be set up as a 1 input/4band or 2 input / 2 bands per channel device, and the filter side chain may be monitored to allow precise tuning of the audio spectrum to be effected.

They have a manual with a handy block diagram to tell what is happening.

Hey pucho812,

Yes, exactly! Unfortunately, the DPR901 was discontinued. I found the schematics in the schematics section of this forum a few months ago and took a few looks in it, but it's reeeeally messy.  (or I'm too picky ;D)

For me, the DPR901 is a true multiband dynamic EQ, whilst the C4 is a multiband compressor with the option of turning it into a dynamic EQ. I find that very useful and therefor went with the C4. Also it's such a widely know plugin, it's almost weird that there is no analog doppelganger.

Börje