|
| | DiodeBridgeGainT () |
| void | prepare (double) |
| | Present for lifecycle symmetry with the rest of the catalog.
|
| void | reset () |
| void | set_character (double character01) |
| | 0..1 colour depth.
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| void | set_adaa (bool on) |
| | Off is for measurement only — it is what the alias-reduction test compares against.
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| double | drive () const |
| | The internal operating amplitude full-scale audio is mapped to.
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| double | control_drive_for_current (double amperes) const |
| | The control drive produced by a physical bias current, in amps.
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| double | dynamic_resistance (double amperes) const |
| | The bridge's small-signal dynamic resistance at a bias current, in ohms.
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| SampleType | process (SampleType input, double control_drive) |
| | One sample.
|
|
| static double | gain_for_control_drive (double control_drive) |
| | g = 1/(1 + x).
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| static double | control_drive_for_gain_db (double gain_reduction_db) |
| | x = 10^(|GR|/20) − 1, the drive that realises a given (negative) gain reduction in dB.
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| static double | curvature (double control_drive) |
| | β(x) = β0·(1 + κ·x) — the curvature in force at a given control drive.
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| static double | shape (double s, double beta) |
| | The odd cubic the balanced bridge imposes, with slope exactly 1 at the origin: shape(s) = s − β·s³/3.
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| static double | shape_antiderivative (double s, double beta) |
| | ∫shape ds = s²/2 − β·s⁴/12.
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| static double | max_operating_amplitude (double beta) |
| | Where the cubic stops being monotonic, less the safety margin.
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| static double | third_harmonic_ratio (double s, double beta) |
| | Closed-form third-harmonic ratio of the shaper for a sine of amplitude s at curvature β, from the identity sin³θ = (3sinθ − sin3θ)/4:
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| static constexpr double | kIdeality = 1.9 |
| | Emission coefficient of the bridge diodes.
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| static constexpr double | kSaturationCurrent = 1e-14 |
| | Reverse saturation current of one bridge diode.
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| static constexpr double | kSeriesResistance = 1000.0 |
| | Series reference resistance the bridge's variable resistance divides against.
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| static constexpr double | kBaseCurvature = 0.5 |
| | Base audio-path curvature, at rest.
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| static constexpr double | kDriveCurvature = 0.6 |
| | How fast curvature grows with control drive — the smooth-at-rest → overdriven-when-driven slope, as a slope rather than an adjective: β(x) = β0·(1 + κ·x).
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| static constexpr double | kDriveBridgeMax = 0.20 |
| | Internal operating amplitude at character = 1: full-scale audio maps to |s| ≤ kDriveBridgeMax, comfortably inside the monotonic region.
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| static constexpr double | kDriveBridgeFloor = 0.3 |
| | Fraction of kDriveBridgeMax still applied at character = 0.
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| static constexpr double | kMaxControlDrive = 30.62 |
| | Assumed worst-case control drive, used only to size the monotonicity guard's headroom claim.
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| static constexpr double | kMonotonicMargin = 0.98 |
| | Fraction of the 1/√β monotonicity limit the input clamp uses.
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| static constexpr double | kAdaaEpsilon = 1e-5 |
| | ADAA ill-conditioning guard on |s[n] − s[n−1]|.
|
template<typename SampleType = float>
class pulp::signal::DiodeBridgeGainT< SampleType >
The diode bridge as a gain element: an exact 1/(1 + x) divider plus the audio-path curvature that divider's diodes actually impose.
The gain magnitude is not where the colour lives. That is deliberate and it is the point of the topology: the divider realises the requested gain reduction to within floating-point, and the harmonics come from a separate, separately-scaled shaper. A caller that wants gain reduction with no colour sets character low; a caller that wants colour at unity gain drives the shaper with control_drive = 0.
Small-signal gain is exactly g (series law 1). The shaper is applied to s = drive·u and divided back by drive, so its contribution to the input→output slope at the origin is shape'(0) = 1 identically, at every character setting. Without that normalisation the character knob would be a hidden level control of up to −24 dB, which is precisely the defect series law 1 exists to prevent.
template<typename SampleType = float>
The control drive produced by a physical bias current, in amps.
This is the one place (Is, n, V_T, Rs) are visible, and it is computed THROUGH the shared junction law rather than by restating Shockley's equation: the bias point is the junction's own conduction knee at that current, and 1/r_d is the junction's own incremental conductance there. x = Rs/r_d follows. Exposed because "resistance is inversely
proportional to bias current" is the claim the whole topology rests on, and a claim a test can check is worth more than one it cannot.
template<typename SampleType = float>
Closed-form third-harmonic ratio of the shaper for a sine of amplitude s at curvature β, from the identity sin³θ = (3sinθ − sin3θ)/4:
shape(s·sinθ) = s(1 − β·s²/4)·sinθ + (β·s³/12)·sin3θ
THD3 = (β·s³/12) / (s(1 − β·s²/4)) = β·s²/12 / (1 − β·s²/4)
static double shape(double s, double beta)
The odd cubic the balanced bridge imposes, with slope exactly 1 at the origin: shape(s) = s − β·s³/3.
Definition diode_bridge_compressor.hpp:293
Stated as a shipped function, not as a test-side literal, so the acceptance suite compares the measurement against the model rather than against a number someone typed. (The spec's worked example gives β·s²/3, which drops the factor of 4 from the sin³ expansion — see the module's defect log.)
template<typename SampleType = float>
ADAA ill-conditioning guard on |s[n] − s[n−1]|.
Must sit far below a typical sample-to-sample increment of the drive-scaled signal (at 1 kHz, full scale, character = 1, that increment is ~2.6e-2) and far above float epsilon. [design parameter] default 1e-5, range 1e-7 .. 1e-4.
template<typename SampleType = float>
Base audio-path curvature, at rest.
Tuned to the documented "low
distortion by design" regime — see third_harmonic_ratio() for what it buys in measurable terms. Honest gap: no public measured THD-vs-drive curve for this bridge exists at citable precision. This, kDriveCurvature and kDriveBridgeMax are original engineering tuned to the documented QUALITATIVE behaviour, not lifted from hardware. [design parameter] default 0.5, range 0.0 .. 1.5.
1.15.0