AP Mastering Class-A [WiN]

• Product: Class-A
• Developer: AP Mastering
• Version: 2.3.0
• Format: VST3, AAX
• Requirements: Windows 10 or later
• Source: apmastering.com/plugins/class-a

Class A is an asymmetric saturation plugin from AP Mastering, modeling the even-order-harmonic-heavy distortion character associated with single-ended Class-A mic preamp circuits like the Neve 1073’s input stage. It sits as a coloration insert on a track, bus, or master, with independently selectable saturation types for the positive and negative sides of the waveform and a Q point control shifting harmonic balance toward even orders. Version 2 adds a separate 3D waveshaping mode, an extended ±48dB gain range, and a purpose-built meter for reading levels once that range is engaged.

Key Takeaway

The core value is genuine asymmetric saturation control — independent positive/negative saturation types plus a Q point shifting harmonic balance — visualized through a transfer-function display rather than a fake output waveform. The version 2 trout waveshaper runs as a separate mode: selecting it deactivates the original saturation controls rather than extending them.

Asymmetry Drives Even-Order Harmonics

Class A applies saturation asymmetrically, with independent saturation type selection for the positive and negative halves of the waveform rather than one curve mirrored across both. Raising the Q point — a control borrowed from the DC bias terminology of physical Class-A amplifier design — shifts the waveform’s zero-crossing point off-center, and that asymmetry is what generates even-order harmonics rather than the odd-order harmonics a symmetric saturation curve produces.

A symmetric saturation setting with the Q point at its center produces a more conventional, odd-harmonic-heavy distortion character; pushing the Q point and increasing asymmetry between the positive and negative saturation types shifts that balance toward the thicker, more even-harmonic-dominant character associated with single-ended Class-A circuits like the Neve 1073’s input stage.

A Curve, Not the Actual Signal

A large, slow-moving sine wave on the interface displays the plugin’s internal transfer function rather than the actual processed audio output — the wave itself is unrelated to the input signal and exists purely to show what the saturation curve is doing to any waveform passed through it, since displaying the real output against a musical signal would render as an unreadable, fast-moving mess.

That separation between visualization and actual signal means the sine wave reads the same regardless of what’s playing through the plugin — a kick drum and a vocal produce identical transfer-function displays for the same saturation settings, since the display shows the curve itself, not a response to the specific material running through it.

Parallel, Series, or Nothing at All

Three selectable routing objects change how a resonant, proportional-Q bell boost interacts with the saturation stage. Selecting the banana object sends that resonant boost through saturation in isolation, then blends the processed result back with the unprocessed dry signal in parallel. Selecting toast applies the same resonant boost to the entire input signal in series before it reaches saturation, rather than processing an isolated, parallel copy.

The XLR object is the default selection and applies no resonant boost at all — it routes the input signal directly into the saturation algorithm unmodified, which is accurate to how an actual XLR cable behaves in a real signal chain. A user expecting the XLR selection to add its own coloration gets a transparent pass-through instead, with saturation still active downstream of it.

Trout Replaces the Saturation Controls

The trout object, added in version 2, is an 8-by-8-point 3D waveshaper using Catmull-Rom spline interpolation across its Z-axis, distinct from the plugin’s original saturation algorithm rather than an extension of it. Moving the object vertically increases the effect’s intensity, and rotating it horizontally morphs the waveshaping curve through the eight available grids, with the resulting transfer function displayed on the same visualization used for standard saturation.

Selecting trout deactivates several of the regular saturation controls, since the waveshaping effect runs as a separate processing path rather than an extension of the asymmetric saturation engine — a setting built around independently tuned positive/negative saturation types and Q point isn’t available at the same time as the trout waveshaper on the same signal.

The Curly Meter Only Matters in Boost Mode

A gain boost button doubles the plugin’s input and output gain range from ±24dB to ±48dB, and a linking control ties output gain down as input gain rises, holding rough level consistency while pushing the input harder into saturation. A delta button reverses polarity between input and output, useful for null-testing what the plugin is actually adding once output loudness is matched back to the input level by ear.

Standard metering reads as pinned at 0dBFS once gain boost pushes a signal into that extended range, so the plugin includes a separate curly meter built specifically to work with gain boost engaged — it wraps past 0dBFS instead of clipping visually, reaching +12dBFS on its first wrap and +24dBFS at full travel. Outside of gain boost mode, that curly meter has nothing extra to show over the standard meter, since the standard range covers the full ±24dB the plugin runs at by default.

FAQs