The Waveulator: Two VCA-based Clipper Saturators

[mediatechnology]

I think the first one I do will be ±15V powered.

The expansive mode is something I'm cautious about unless used in extreme moderation.
On the first board I may make that switchable with a header connection to an optional switch.

At the moment I see the current iteration as a tool at the end of the mastering chain, immediately prior to conversion, to control peak level thereby reducing crest factor. The reduced crest factor results in reduced overall level allowing RMS level, "density," to be increased simply by adding make-up gain instead of using average or RMS-responding compression. It's a one-trick loudness pony.

At the point the one trick loudness pony becomes audible in terms of harmonic coloration it breaks things.

To produce an effect I'm thinking the log-expo (linear) control scaling of the original has more promise. It could produce a really thick coloration to the point of sounding de-tuned at max settings. IIRC all of the original samples had log-expo scaling. Linear scaling wasn't suited for complex material but it worked very well on guitar and percussion. Simple tonal structures or transient material are better suited - complex tonal structures intermodulate more and seem to break up faster than linear-expo. Linear-expo is "over easy" log-expo is "over hard."

One other thing I want to pursue with the current version is HF limiting for vinyl cutting. You generally don't want to brickwall material for vinyl. Due to pre-emphasis it actually works against you and sounds like dog poo. What I was thinking about doing was using an inverse-RIAA going into the Wavelator, using it to peak limit the pre-emphasized signal and then applying RIAA de-emphasis. It may be a useful sibilance control tool.

Due to appliance and yard entropy it may be a few days before I can get back to the Protoboard.

[emrr]

Intriguing

[TheeAldeen]

i like the direction this is going as level control

this new unit at the end of synth summing bus I have on the bench would be very helpful to pad down the signal from the send return to ka-width

- the width has such a dynamic input/out range - if the waveulator has a gain control element & threshold - it could be used to pad down and trim the signal from the width controller, which is after the send & return

- using outboard effects - the send/returns a very hot signal signal - one that the ka-width has had [zero] issues handling so far —

the ability to trim that massive ~+27dbu output down befor converters is huge — please put me down for 2-units

[TheeAldeen]

I understand adding gain stages is simple - yet added to the cost -

if the unit has a gain element & buffer to accept high dbu levels, bring them down/up, with threshold & output trim - that would be helpful

nothing insane is needed but as stated / the ka-width has worked wonders handling the high synth voltages from the outboard effects - some of the effects like the neon egg kick out a massive output voltage to be used with modular & euro rack

the width controller has zero issue with these with its massive dynamic range - but the signal always has to be brought down before converters -

Anyway you can engineer that into the design - I would appreciate it & use the added features gratefully

[TheeAldeen]

** as stated before - whatever you guys all end up deciding on and whatever Wayne puts together will be enough - I’m not very picky - and the application of whatever features are in the final version or prototypes will easily be made due **

[mediatechnology]

The makeup gain is just an offset injected into the VCA Ec driver.
It's a DC level controlled by a pot and a resistor into an existing summing node.

The sidechain looks almost exactly like any feed-forward compressor/limiter except there is no averaging in the detector.

[mediatechnology]

I finally had a chance to return to the Protoboard and have added the makeup gain and some buffer stages around the ratio pot.
Also added a -12V reference supply and adjustable 0 dBFS reference for the Threshold control.

The 0 dBFS reference works like this:
Let's say the converter overloads at 2V RMS which we'll round to +8 dBu.
2V RMS/+8dBu is about 2.75V peak.
Put another way 0 dBFS is 2.75V peak.
The user would adjust a DC trim to 2.75VDC making the 0dBFS Threshold setting, at full CW rotation, equal to the overload point of the converter.
The Threshold control would range from -20 dBFS at full CCW rotation to 0 dBFS at full CW.
Scaled this way the user can dial in the rotation point below overload and begin the process of setting a target headroom in dB.

The next control is Ratio which sets the slope above threshold.
Hardness, set by ratio, then controls the level excursion allowed above threshold.
There can actually be gain reversal if set high enough where the signal begins to fold back on itself.

The makeup gain ranges from 0 to +12 dB using a pot.
A 12 position switch, in 1 dB steps would range from 0 to +11 dB.
"It goes to 11."

The controls are nearly identical to a conventional above threshold limiter.
Whats missing are attack and release which are "0."

I've been metering gain reduction on the 'scope at the wiper of the ratio control and that looks to be the best sample point for metering.
The GR meter would need to be peak-responding with a modest hold time.
The scaling is linear dB per volt.

The transfer function provides a real picture of what the Waveulator does because it shows "hardness" in the ratio setting.
I'll be providing auxiliary "X Y" outputs so that input level (X) can be compared to output level (Y) in real time on a goniometer.
The Threshold rotation point, Ratio (Hardness) and Make-up Gain are super easy to set this way and it provides great at-a-glance visualization.

The K-Meter (or a DAW level meter displaying peak and RMS) is also useful and can with little interpretation be used instead of a dedicated GR meter or goniometer.
What the K Meter can't display is hardness.

The Waveulator's Ratio control defies meaningful panel markings for calibration.
Since the detector is linear and the VCA exponential-responding the actual numeric slope depends a lot on the level range it's operating at.
It can't be calibrated in the familiar 1:1, 1.2:1, 1.4:1, 2:1 etc. panel marks because where 1.2: falls on the dial varies considerably with the threshold and signal level.
For a Ratio potentiometer 0-10 seems to make the most sense or for a 12 position switch - wait for it - 0 to 11.

I'm close to starting schematics but do have various tweaks to do optimizing component values.

Will also be cutting a demo and posting it demonstrating how squashing the peaks allows RMS levels to be increased by a similar amount.
The loudness differences are huge and converter overload is avoided.

[emrr]

Sounds good

[mediatechnology]

Here is a preliminary schematic for the Waveulator ME "Mastering Edition"

I still need to draw sheet 2 after I figure out the metering. I plan on using a single channel version of this one modified for peak: https://proaudiodesignforum.com/forum/p ... php?t=1162

It may also need a "winky" LED for threshold. For the meter display I think I'll put the drivers on the mainboard and then have an LED display board connected by a ribbon cable.


Waveulator ME Mastering Edition Schematic 081023

I'll post a circuit description soon.

[mediatechnology]

Another demo.
On this one I applied about 6-8 dB of peak-limiting and then used makeup gain to increase overall peak level, and RMS, back to approximately -1 dBFS.
The first portion of the file is unprocessed, the second segment is processed.

https://proaudiodesignforum.com/content ... cessed.wav







There's about a 5dB increase in signal power.
If I had normalized the peak level of the second segment back to the level of the unprocessed there would be a slightly higher RMS level.