A Quadrature Power-Summed Compressor Sidechain For "The Uno Compressor"

[Gold]

I've had an interest in a de-esser/sibilance controller for vinyl and have wanted to wrap my head around the BSB74.
It would need to be a dedicated box..

Jakob Erland once described it as S&M engineering. With the inductor based delay line. I have the BSB74 literature. If you need anything let me know. I may also have some Ortofon 732 literature. There of course are no Maselec schematics available. I haven’t tried to figure out what’s going on. I didn’t see a VCA though. Maybe a four quadrant multiplier?

[mediatechnology]

I've had an interest in a de-esser/sibilance controller for vinyl and have wanted to wrap my head around the BSB74.
It would need to be a dedicated box..

Jakob Erland once described it as S&M engineering. With the inductor based delay line. I have the BSB74 literature. If you need anything let me know. I may also have some Ortofon 732 literature. There of course are no Maselec schematics available. I haven’t tried to figure out what’s going on. I didn’t see a VCA though. Maybe a four quadrant multiplier?

I need to download the original AES paper. I have the schematics.

[mediatechnology]

Updated schematic 4/8/24. I added a simple Sidechain HP filter ahead of the Dome filter.



Though there appear to be a lot of op amps they can all be TL072.
No attempt is being made to reduce component count because it's not a mass-produced product.
Accuracy of stepped switch settings are the goal for the buffers and added trims.
When switches are used the slugging resistors will be removed.

[JR.]

Deessing in a final stereo mix is kind of after the horse has already left the barn. Generally excessive sibilance is caused by too close miking hot instruments (like cymbals). Hot HF content quickly attenuates traveling through air to a less close mic.

Of course that does not help after the fact. The strategy I adopted was to use fast attack and fast release while applying the deess gain reduction to both channels so the stereo mix doesn't get altered.

A simple deesser is a cheap add-on with perhaps decent value for the modest incremental cost. I wouldn't attempt to try to make a dedicated after the fact deesser. To do that well, some look ahead delay might be useful to anticipate gunshots or lightning strikes for limiting.

Delay is another thing that digital might be better at, but I am not suggesting that.

JR

[mediatechnology]

The units Paul and I are talking about (e.g. Neumann BSB74, Maselec MDS2) are specific to vinyl cutting and are typically used when the sibilance - or any excessive HF energy - isn't a problem in other mediums. Inverse RIAA, an acceleration-limited mechanical system, cutterhead power limits and power amp headroom all conspire against excessive HF energy which might not be from an acoustic instrument at all.

The sidechain high pass filter I'll be adding will be to limit bass compression switchable from around 40-240 Hz. I'm thinking single-order ought to be sufficient and simple. The sidechain filter has to be stereo so I want to keep the switch 2 poles or the pot two gang.

[JR.]

Thanks for the explanation, kind of like the step the old sweetening engineers performed.

JR

[Gold]

I’d just add that the high frequency limiters I’m referencing work exceptionally well on single instruments. They are just overkill for most. The BSB74 was never sold as a standalone unit. Only as part of the cutting rack. The Maselec was 2-4X the price of most other de essers. Now that they are no longer being made the price has shot up even more.

There is definitely room for a commercial unit.

[emrr]

Yes de-ess is still a thing for single sources, and Paul can tell us how much he needs to use it now versus then on program for cutting vinyl, still a growing trend.

I have software de-essers that work well, but sometimes the dox 902 still wins, and if I'm purposefully smashing drums through a limiter while tracking, sometimes the 902's in hi-freq limit mode are perfect for keeping cymbals at bay.

[Gold]

YPaul can tell us how much he needs to use it now versus then on program for cutting vinyl, still a growing trend.

High frequency limiters have always been necessary for lacquer cutting. The earliest stereo cutting electronics had them. The Ortofon 632 was part of the first generation tube cutting electronics. Late 1950's early 1960's. The Neumann VG1 tube electronics also had a high frequency limiter. The solid state Neumann VG66 I use has a built in high frequency limiter (HK66). It is not very useful. It's constructed around a FET gain reduction element with a band pass filter at 12k Hz in the side chain. It's slow and is always not enough or too much.

[mediatechnology]

Latest schematic.
I added a low frequency single-order high pass filter to the sidechain.
With the values shown, the maximum frequency is about 240 Hz.
Added series resistance at the Phoenix connector lowers the frequency.
When fully open-circuit Fc is about 7 Hz.

Jumpers at the output of the Dome filter allow it to be bypassed for a low frequency "color" mode.



A modified Waveulator schematic showing the VCA audio path and gain reduction metering will become sheet 1.