DSP and Tuning Technology

01 The Hybrid DSP Engine

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.

02 Railsback Stretch Tuning Model

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:

Using a Railsback stretch curve approximation, the tuner flatters the bass notes (stretching them slightly flat to match the lower partials of the mid-range) and sharpens the treble register (matching their fundamental frequencies to the high overtones of the lower keys). This produces clean, sweet triads and brilliant, resonant unison segments that feel native to high-end acoustic grand pianos.

03 Physics-Based Tuning Profiles

Ivory Pro provides six tailored presets that dynamically adjust the DSP and physical feedback parameters to suit specific instruments and environments:

04 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.

05 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.