# Technical Specification: Advanced Editing Toolset & Volume Automation Envelope on Sub-Tab This document defines the interactive layout design and signal processing algorithms for the advanced localized editing toolset contained within the isolated temporary document workspace (Sub-tab). --- ## 1. Target Selection Scope The toolset within the Sub-tab environment supports two target operational boundaries: * **Global Clip:** When no specific timeline selection highlighted mask is present, all active DSP effects apply uniformly across the entire length of the extracted Audio Clip. * **Selected Range:** When an explicit timeline segment $[T_{\text{start}}, T_{\text{end}}]$ is highlighted by the user, DSP routines calculate changes exclusively inside those boundaries. Splice junctions automatically compute crossfades to mitigate transient click/pop anomalies. --- ## 2. Ruler-Based Tools These utilities display as intuitive, linear slider scales (Sliders/Rulers) embedded in the top toolbar row: ```text [ Normalize: |======o======| 0 dB ] [ Gain: |====o====| +3 dB ] [ Pitch: |==o==| -2 Semi ] ``` ### 2.1. Peak Normalization * **UI Layout:** A slide scale control allowing users to configure target amplitude thresholds variable from $-12\text{ dBFS}$ down to $0\text{ dBFS}$. * **DSP Math Algorithm:** Locate the maximum absolute peak amplitude value $A_{\text{max}}$ within the targeted area, then multiply all active samples by a static scalar gain multiplier $G$: $$G = \frac{10^{\frac{\text{Target\_dB}}{20}}}{A_{\text{max}}}$$ ### 2.2. Volume Up / Down (Quick Gain) * **UI Layout:** A linear sliding ruler modulating the overall absolute gain structure of the focused segment. * **Operational Range:** Adjustable from $-\infty\text{ dB}$ (complete mute attenuation) up to $+12\text{ dB}$ of linear amplification. ### 2.3. Pitch Shifting * **UI Layout:** A calibrated slider modifying the project's fundamental frequencies discrete in semitones or cents. * **Operational Range:** Boundaries map from $-12\text{ semitones}$ (one octave down) to $+12\text{ semitones}$ (one octave up). * **DSP Engine Routine:** Employs a spectral Phase Vocoder to shift frequencies without affecting the physical, real-time duration layout of the segment. --- ## 3. Graph-Based Fades Fading curves overlay graphically directly onto the highlighted waveform canvas region, enabling precise boundary attenuation adjustments: ```text Linear Fade-In Exponential Fade-Out +───────────────────────────+ +───────────────────────────+ | /███████████████| |███████████\ | | / ███████████████| |███████████ \ | | / ███████████████| |███████████ \___ | | / ███████████████| |███████████ \______| +───────────────────────────+ +───────────────────────────+ |<──────── Fade-In ────────>| |<─────── Fade-Out ────────>| ``` * **Fade-In:** Multiplies an ascending amplitude ramp from $0.0$ to $1.0$ at the starting index profile of the selection region. Users can toggle between **Linear** or **Exponential** curves to achieve a smoother, more psychoacoustically natural volume build-up. * **Fade-Out:** Multiplies a descending amplitude decay ramp from $1.0$ down to $0.0$ at the trailing boundary edge of the selection range. --- ## 4. Ruler Percentage Stretch Tool A dedicated percentage metric scale control (`Ruler %`) sitting on the control toolbar dictates time-stretching and playback velocity parameters: ```text [ Speed Stretch %: |========o========| 100% (Native) ] -> Range: 50% (Half Speed) - 200% (Double Speed) ``` * **Interaction Mapping:** Users drag the percentage slider node or hold down the `Alt` key and drag the rightmost boundary edge of the clip along the horizontal axis to change this scale metric. * **Sync Formula:** Let $D$ map to the unscaled native duration value, and $D'$ map to the target modified duration footprint. The resulting structural playback speed ratio percentage ($S$) is given by: $$S = \frac{D}{D'} \times 100\%$$ * **UI Representation:** A bright yellow text metadata indicator (e.g., `Speed: 85.3%`) is rendered at the top-left section of the audio clip bounding boundary. --- ## 5. Ultra-Zoom & Zero-Crossing Alignment To facilitate precision structural slicing at sample-level resolutions, the sub-tab canvas allows microscopic viewport expansion: ```text MICRO VIEWPORT ZOOM (ULTRA ZOOM-IN) +─────────────────────────────────────────────────────────────────+ | Waveform renders discrete contiguous sample nodes explicitly | | ○ (Sample i) | | / \ | | ─────────────────/───\─────────────────────────────► 0V Axis | | \ ○ (Sample i+2) | | \ / | | \_○ (Sample i+1 - Zero-Crossing Point)| +─────────────────────────────────────────────────────────────────+ ``` * **Upper Viewport Scaling Limit:** Allows zooming in up to an extreme lower threshold of $2000\text{ pixels/second}$. At this zoom metric, layout compilation transitions away from downsampled peak profiles (Peak Waveform) to render actual discrete **sample nodes** interconnected by fine lines. * **Zero-Line Snapping Logic:** When establishing selection boundaries, the tracking loop automatically snaps the horizontal selection cursor coordinate to the nearest available sample address exhibiting an algebraic phase inversion (sign change): $$x[i] \cdot x[i+1] \le 0$$ --- ## 6. Top Duration Timeline Directly above the isolated sub-tab waveform canvas lane, a dedicated horizontal measuring ruler tracks clip timing data: ```text | 0:00.000 | 0:01.000 | 0:02.000 | 0:03.000 | 0:04.000 (Duration: 4.152s) +───────────────────────────────────────────────────────────────────────────────────────+ | [==================== VÙNG QUÉT CHỌN (RANGE SELECTION) ====================] | +───────────────────────────────────────────────────────────────────────────────────────+ ``` * **Total Duration Monitoring:** Renders the absolute, precise time extent of the isolated audio block in the right-hand corner of the timeline ruler layout (e.g., `Duration: 12.450s`). * **Duration Selection Drag:** Left-clicking and dragging horizontally inside this top duration bar defines a highlighted selection overlay window. This range indicator automatically projects down into the waveform lane underneath. --- ## 7. Bottom Transport Panel A prominent master transport toolbar occupies the bottom row layout of the sub-tab layout to manage audio playback monitoring: ```text +───────────────────────────────────────────────────────────────────────────+ | [Back to Start] [Play] [Pause] [Stop] | Loop Sequence: [X] | +───────────────────────────────────────────────────────────────────────────+ ``` * **Back to Start:** Instantly updates the regional playhead time parameter back to the absolute starting point ($t = 0.0\text{ s}$). * **Play / Pause / Stop:** Drives regional audio engine playback loops restricted entirely to the data buffers allocated inside the current sub-tab workspace. * **Loop Toggle:** Toggles continuous cycle loops over the highlighted section or the whole clip. --- ## 8. Volume Automation Envelope (Pen Tool) This advanced timeline automation layer allows audio designers to draw custom gain curves over the background waveform graphics. ```text VOLUME AUTOMATION ENVELOPE (PEN TOOL) +3 dB ────────────────────────────────────────────────────────────── \ Node 1 Node 3 \ ○ ○ 0 dB ───\────/─\─────────────────────────────────────/─\─────────── (0 dB Unity Gain Axis) \ / \ / \ \/ \ / \ ○ \_______________________________/ \________ Node 2 Node 4 -30 dB ────────────────────────────────────────────────────────────── |<─────────────────── Horizontal Axis (Time) ─────────────────────>| ``` ### 8.1. Pen Tool Interaction Mechanics * **Activation:** Clicking the designated Pen Tool icon in the control panel modifies the pointer device presentation into a drawing crosshair or pencil graphic. * **Envelope Initialization:** Activating the Pen Tool generates a solid horizontal neon green line representing $0\text{ dB}$ (Unity Gain) across the track workspace, acting as the baseline master axis. * **Drawing Automation Curves:** * Left-clicking anywhere along this line creates an adjustable anchor point (**Control Node**). * Dragging an initialized control node upward increases signal amplitude (up to a maximal ceiling boundary of $+3\text{ dB}$). * Dragging a control node downward reduces signal amplitude (down to a lower attenuation floor of $-30\text{ dB}$). * The graphics framework automatically updates straight vector paths between sequential nodes utilizing simple linear interpolation. ### 8.2. DSP Volume Envelope Math Given two chronologically adjacent drawn points $P_1(t_1, V_1)$ and $P_2(t_2, V_2)$, the targeted instantaneous decibel gain variable $V_{\text{dB}}(t)$ at an arbitrary time index $t$ ($t_1 \le t \le t_2$) matches the following linear equation: $$V_{\text{dB}}(t) = V_1 + (t - t_1) \cdot \frac{V_2 - V_1}{t_2 - t_1}$$ This decibel value must be translated into a standard linear gain scalar coefficient $G_{\text{linear}}(t)$ to multiply it into the core audio sample stream values: $$G_{\text{linear}}(t) = 10^{\frac{V_{\text{dB}}(t)}{20}}$$ $$x_{\text{automation}}[n] = x[n] \cdot G_{\text{linear}}\left( \frac{n}{\text{Sample Rate}} \right)$$ --- ## 9. Python Porting Manual (Docker Server Platform) When translating these graphical volume automation envelope features to a desktop PyQt6 interface or an asynchronous Celery Docker worker pipeline, the standard scientific function `numpy.interp` handles array vector scaling processing loops: ```python import numpy as np def apply_volume_automation_envelope(y: np.ndarray, sr: int, nodes: list) -> np.ndarray: """ Applies a user-drawn volume automation envelope onto an acoustic signal NumPy array. nodes: A list of point dictionaries, e.g., [{"time": 0.0, "db": 0.0}, {"time": 2.5, "db": -12.0}, ...] """ if not nodes: return y # Sort envelope nodes chronologically by time axis nodes = sorted(nodes, key=lambda x: x["time"]) # 1. Map node variables into distinct coordinates arrays node_times = np.array([node["time"] for node in nodes]) node_dbs = np.array([node["db"] for node in nodes]) # Hard-clamp boundary constraints matching the operational floor [-30.0dB, +3.0dB] node_dbs = np.clip(node_dbs, -30.0, 3.0) # 2. Evaluate absolute timeline timestamps for every index position inside the signal array total_samples = len(y) sample_times = np.arange(total_samples) / sr # 3. Linearly interpolate localized decibel thresholds across every single sample step interpolated_dbs = np.interp(sample_times, node_times, node_dbs, left=node_dbs[0], right=node_dbs[-1]) # 4. Map logarithmic values into standard linear gain scale arrays linear_gains = 10.0 ** (interpolated_dbs / 20.0) # 5. Multiply the raw amplitude vector array by the linear gain modifier mask return y * linear_gains ```