DSP and Tuning Technology

01 The Hybrid DSP Engine & Calibration

Traditional tuners utilize a single algorithm (such as a generic FFT or basic autocorrelation) across the entire range. This fails to handle the physics of a piano, where the lowest strings have virtually no fundamental frequency and the highest strings decay too rapidly for standard correlation. Ivory Pro uses a dynamic two-tier hybrid DSP pipeline:

• McLeod Pitch Method (NSDF) with Octave Filter (A0 to A6): Low-frequency tracking relies on the Normalized Square Difference Function. It is normalized per lag, preventing high-frequency harmonics from overriding the fundamental. When a missing fundamental in the lowest octave (A0-B0) is played, a sub-harmonic correction algorithm automatically compares subsequent peaks, preventing octave-doubling errors.
• Direct Linear FFT (A#6 to C8): For the short periods of the treble register, the engine switches to a direct FFT search combined with parabolic peak interpolation. Linear magnitude interpolation mathematically corrects the 3-5 cent shifts introduced by standard power-spectrum methods.
• Extreme Treble Improvements (B7 & C8): Four targeted refinements were made for the top two keys: a sample-rate-aware treble lag limit (scales correctly at 48 kHz and 96 kHz), a reduced NSDF threshold (0.25) in the B7/C8 sub-band for inharmonic strings, a relaxed FFT SNR requirement near the Nyquist limit, and a more sensitive octave-doubling correction path covering B6→B7 and C7→C8.
• Auto-Calibrate A4 Reference Pitch: Support for non-standard reference pitches (436–444 Hz) with sub-cent accuracy. Technicians can auto-calibrate the reference frequency by tapping the Auto-Calibrate button, which listens to a sustained external tuning fork or reference tone for 3 seconds, filters out noise, and aligns the tuner using a median calculation.
• Harmonic Spectrum Analyzer (FFT Plot): A specialized 60fps high-resolution visual spectrum analyzer overlays the main tuning view. By feeding raw sample data through an un-windowed FFT pipeline directly to the UI, technicians can instantly visualize inharmonicity, isolate false beats, and balance overtone amplitudes with scientific precision.

02 Phase-Locked Strobe Tuning Visualizer

The ultimate standard for absolute tuning accuracy isn't a digital needle—it's a strobe. Ivory Pro integrates a multi-band concentric strobe ring visualizer that natively integrates with the core pitch extraction phase.

• Dynamic Concentric Rings: Three interlocking strobe rings correspond to the fundamental, second, and third harmonics.
• Continuous Phase Rotation: The strobe rings rotate proportionally to the exact cents offset. Flat pitches spin counter-clockwise, sharp pitches spin clockwise. When the string perfectly aligns with the target frequency, the rings freeze and lock into a glowing emerald state, confirming sub-cent accuracy.

03 Railsback Stretch Tuning Model & Inharmonicity Wizard

Because piano strings are relatively stiff, their upper partials are physically stretched sharp (inharmonicity). If a piano is tuned strictly to mathematical equal temperament, the harmonics will clash, resulting in harsh-sounding chords. Ivory Pro models this natural stretching in real-time:

Railsback Stretch Curves & Intensity: Pianos default to the Railsback stretch curve with a custom coefficient that adjusts the stretch intensity from 1.0 to 4.0. Users can select profiles like Mild (for spinets or uprights), Standard (for grand pianos), or Deep (for concert grands) to stretch the bass flatter and the treble sharper.

Inharmonicity Profile Builder: Fully custom tuning curves can be generated using our built-in measurement wizard. By playing four reference notes (A1, A3, A5, C6) for 2 seconds each, the DSP engine computes individual string stiffness constants ($B$) via real-time overtone analysis. A log-linear interpolation algorithm maps the constants across all 88 keys to construct a physical tuning curve governed by professional octave-harmonic matching standards (the 6:3 partial rule in the bass, and the 4:2/2:1 rules in the treble register).

04 Historic Temperaments & Pitch Raise Calculator

Ivory Pro features a completely mathematically rigorous temperament and tuning target system built for professional field work.

• Historic Temperaments: Go beyond equal temperament. Easily switch to Werckmeister III, Kirnberger III, or Meantone (1/4 Comma). The engine intrinsically calculates and stores the precise cents offsets per key to guarantee perfectly historically accurate chords.
• Pitch Raise (Overpull) Calculator: When pulling up flat pianos, technicians must tune notes sharp to compensate for soundboard drop. Simply dial in your target percentage (e.g., 25%), and the Lock Overpull feature automatically shifts the visual needle target dynamically based on the current flatness of the string. You tune to the visual "0", and the string settles perfectly to pitch.

05 Physics-Based Presets & Profile Manager

Ivory Pro provides six tailored presets that dynamically adjust the DSP and physical feedback parameters to suit specific instruments. Additionally, the new Client & Piano Profile Manager allows technicians to create, load, duplicate, rename, or delete custom client records, keeping client logs and customized tuning parameters saved directly on the device.

06 Premium Mechanical Metronome

The metronome features a fully modeled visual pendulum animation synchronized directly with our tone synthesis pipeline. You can select mechanical wooden ticks, electric beats, or pitched reference clicks, supporting complex rhythms (1/4, 2/4, 3/4, 4/4, 3/8, 6/8, 9/8, 12/8) with dynamic tap-tempo timing calculations.

07 USB Audio Interface Support

Ivory Pro extends its capture pipeline to any class-compliant USB audio interface, giving professional technicians full control over signal quality at the source:

• Plug-and-Play Detection: The audio engine monitors AVAudioSession route changes and automatically reconfigures for new USB devices — Focusrite Scarlett 2i2, ZOOM iQ7, and all class-compliant USB audio interfaces. No restart or manual setup required.
• Stable Reconnection: A 300 ms debounce filter absorbs the multiple route-change events that USB negotiation emits on connect/disconnect, guaranteeing a single clean rebuild per physical device event.
• Multi-Channel Downmix: Stereo and 4-channel interfaces are automatically mixed to mono in the tap callback using vDSP SIMD arithmetic, so signal is captured regardless of which physical input jack is active.
• Software Input Gain: An adjustable 1×–10× gain stage is applied in the DSP tap before pitch detection. USB interfaces default to 3× boost; the value persists in Settings and is restored automatically when the same class of device is reconnected.
• Live Mic Info Display: A status bar below the level meter shows the active device name, sample rate (44.1 kHz / 48 kHz / 96 kHz), and channel count in real time, highlighted in green when a USB device is active.