feat(plotnine): implement spectrogram-mel

[github-actions]

Implementation: spectrogram-mel - plotnine

Implements the plotnine version of spectrogram-mel.

File: plots/spectrogram-mel/implementations/plotnine.py

Parent Issue: #4672

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🤖 impl-generate workflow

[claude]

AI Review - Attempt 1/3

Image Description

The plot displays a mel-spectrogram with time (0-3 seconds) on the x-axis and mel-scaled frequency (64-8000 Hz) on the y-axis, using a log-frequency scale. The color scheme is an inferno-like palette ranging from deep purple/black (low power, ~-60 dB) through magenta and orange to bright yellow (high power, ~0 dB). The title reads "spectrogram-mel · plotnine · pyplots.ai" in bold centered text. A colorbar labeled "Power (dB)" sits on the right side. Bright horizontal bands are clearly visible at the harmonic frequencies (220, 440, 880 Hz) showing the synthesized tonal components. A prominent diagonal chirp sweep is visible from ~500 Hz at t=0.8s curving up to ~4000 Hz at t=2.0s. The signal amplitude decays over time, with the lower frequencies fading in the 2-3 second range. The panel background is dark (#4) which blends well with the spectrogram's low-energy regions. The plot background is light gray providing good contrast framing.

Score: 87/100

Category	Score	Max
Visual Quality	28	30
Design Excellence	14	20
Spec Compliance	15	15
Data Quality	15	15
Code Quality	9	10
Library Mastery	6	10
Total	87	100

Visual Quality (28/30)

• VQ-01: Text Legibility (8/8) - All font sizes explicitly set: title=24, axis titles=20, tick labels=16, legend title=16, legend text=14. All clearly readable.
• VQ-02: No Overlap (6/6) - No overlapping text elements. Y-axis log-spaced labels well separated.
• VQ-03: Element Visibility (5/6) - Tiles are visible and convey the spectrogram well, but lower-frequency region appears somewhat blocky with visible tile boundaries.
• VQ-04: Color Accessibility (4/4) - Custom inferno-like sequential palette is perceptually uniform and colorblind-safe.
• VQ-05: Layout & Canvas (3/4) - Good 16:9 layout. Plot fills canvas well but colorbar is relatively small and some right-side space could be better utilized.
• VQ-06: Axis Labels & Title (2/2) - "Time (s)" and "Frequency (Hz)" are descriptive with units.

Design Excellence (14/20)

• DE-01: Aesthetic Sophistication (6/8) - Thoughtful custom color palette (manually specified inferno gradient), dark panel background (feat: add complete automation infrastructure for plot generation #4) matching the colormap's low end, light gray plot background for framing contrast, bold centered title with good typography hierarchy. Goes clearly above library defaults.
• DE-02: Visual Refinement (4/6) - Grid lines removed entirely, panel background styled to blend with spectrogram, margins set. Good attention to detail but colorbar could be taller/more prominent.
• DE-03: Data Storytelling (4/6) - The synthesized signal tells a clear story: harmonic structure visible as horizontal bands, chirp sweep creates a dramatic diagonal focal point, time-varying amplitude decay visible. Viewer immediately sees the audio structure.

Spec Compliance (15/15)

• SC-01: Plot Type (5/5) - Correct mel-spectrogram with mel-scaled frequency axis.
• SC-02: Required Features (4/4) - dB scale ✓, sequential colormap ✓, time in seconds ✓, mel-scaled Hz labels ✓, colorbar in dB ✓, n_fft=2048 ✓, hop_length=512 ✓, n_mels=128 ✓, synthesized audio ✓.
• SC-03: Data Mapping (3/3) - X=time(s), Y=mel frequency(Hz), fill=power(dB). All correct.
• SC-04: Title & Legend (3/3) - Title "spectrogram-mel · plotnine · pyplots.ai" in correct format. Colorbar properly labeled "Power (dB)".

Data Quality (15/15)

• DQ-01: Feature Coverage (6/6) - Shows harmonics (220, 440, 880 Hz), chirp sweep, time-varying amplitude decay, noise component — demonstrates multiple aspects of audio spectral analysis.
• DQ-02: Realistic Context (5/5) - Audio analysis with realistic sample rate (22050 Hz), speech-like frequency components, plausible audio ML preprocessing scenario.
• DQ-03: Appropriate Scale (4/4) - Frequencies in human hearing range, 3-second duration, realistic dB scale (0 to -60).

Code Quality (9/10)

• CQ-01: KISS Structure (3/3) - Linear flow: imports → data synthesis → STFT → mel filterbank → DataFrame → plot → save.
• CQ-02: Reproducibility (2/2) - np.random.seed(42) set.
• CQ-03: Clean Imports (2/2) - All imports used (numpy, pandas, plotnine components, scipy.signal.stft).
• CQ-04: Code Elegance (1/2) - The mel filterbank construction uses nested Python for loops (O(n_mels × n_freq_bins)) which is verbose and slow. Could be vectorized with numpy broadcasting.
• CQ-05: Output & API (1/1) - Saves as plot.png, uses current plotnine API.

Library Mastery (6/10)

• LM-01: Idiomatic Usage (4/5) - Good grammar-of-graphics composition with ggplot + aes + geom_tile + scale_fill_gradientn + custom scales. Uses plotnine's theming system extensively. The variable tile height via aes(height=) is a solid approach.
• LM-02: Distinctive Features (2/5) - Uses geom_tile with variable height mapping and scale_fill_gradientn, but the approach is fairly standard. The heavy manual data prep (STFT, mel filterbank) is library-agnostic. Could leverage more plotnine-specific features.

Score Caps Applied

• None

Strengths

• Perfect spec compliance — all required features present including mel scale, dB conversion, colorbar, and correct parameters
• Rich, realistic synthesized audio data with harmonics, chirp sweep, and amplitude decay telling a clear audio analysis story
• Thoughtful color design with custom inferno gradient and dark panel background matching the colormap
• Clean grammar-of-graphics composition with explicit font sizing throughout

Weaknesses

• The mel filterbank construction uses nested Python for loops — should be vectorized with numpy broadcasting for cleaner, more elegant code
• The colorbar could be taller and more prominent to better match the plot height
• Lower frequency tiles appear somewhat blocky; tile spacing could be refined for smoother visual appearance

Issues Found

1. CQ-04 MEDIUM: Nested for loop for mel filterbank is verbose and un-Pythonic
   • Fix: Vectorize filterbank construction using numpy broadcasting
2. LM-02 LOW: Library usage is competent but not distinctive
   • Fix: Consider using coord_trans or other plotnine-specific features to enhance the implementation
3. VQ-05 MINOR: Colorbar is somewhat small relative to the plot
   • Fix: Increase legend_key_height for a taller, more prominent colorbar

AI Feedback for Next Attempt

Vectorize the mel filterbank construction using numpy broadcasting instead of nested for loops. Consider increasing the colorbar height (legend_key_height) for better visual balance. Explore plotnine-specific features that could distinguish this implementation from a generic matplotlib approach.

Verdict: REJECTED

[github-actions]

🔧 Repair Attempt 1/3

Applied fixes based on AI review feedback.

Status: Repair completed, re-triggering review...

---

🤖 impl-repair

[claude]

AI Review - Attempt 2/3

Image Description

The plot displays a mel-spectrogram with time (0–3 seconds) on the x-axis and mel-scaled frequency (64–8000 Hz) on the y-axis. The colormap is an inferno-like gradient from dark black/purple (low power ~-60 dB) through magenta and orange to bright yellow (0 dB). Clear horizontal bands of energy are visible at harmonic frequencies (~220, 440, 880, 1320, 3300 Hz), with the lower harmonics being brightest and decaying over time. A prominent chirp sweep arcs from ~500 Hz at t≈0.8s up to ~4000 Hz at t≈2.0s, creating a striking curved bright line. A colorbar on the right is labeled "Power (dB)". The title reads "spectrogram-mel · plotnine · pyplots.ai". The panel background is dark (#4) matching the colormap floor, with a light gray outer background.

Score: 88/100

Category	Score	Max
Visual Quality	28	30
Design Excellence	14	20
Spec Compliance	15	15
Data Quality	15	15
Code Quality	10	10
Library Mastery	6	10
Total	88	100

Visual Quality (28/30)

• VQ-01: Text Legibility (8/8) — All font sizes explicitly set: title 24pt, axis titles 20pt, ticks 16pt, legend 14-16pt. All perfectly readable.
• VQ-02: No Overlap (5/6) — Minor crowding at the bottom of the y-axis where 64 and 128 Hz labels are very close together on the mel scale.
• VQ-03: Element Visibility (6/6) — geom_raster with interpolation produces a smooth, gap-free spectrogram. Harmonics and chirp clearly visible.
• VQ-04: Color Accessibility (4/4) — Inferno-like sequential colormap is perceptually uniform and colorblind-safe.
• VQ-05: Layout & Canvas (3/4) — Good proportions overall. The light gray outer background creates a visible border effect; colorbar is well-positioned but the overall canvas utilization could be tighter.
• VQ-06: Axis Labels & Title (2/2) — "Time (s)" and "Frequency (Hz)" with units. Title in correct format.

Design Excellence (14/20)

• DE-01: Aesthetic Sophistication (6/8) — Custom inferno gradient is well-chosen and manually specified. Dark panel background (feat: add complete automation infrastructure for plot generation #4) matches the colormap floor, creating a cohesive look. Typography is clean and professional. Clearly above defaults.
• DE-02: Visual Refinement (4/6) — Grid lines removed entirely, dark panel background, clean whitespace. The light gray outer background is functional but could be more polished (e.g., matching dark theme throughout or using a more refined border treatment).
• DE-03: Data Storytelling (4/6) — The synthesized audio with decaying harmonics and a chirp sweep creates genuine visual interest. The chirp is a clear focal point that draws the eye. Time-varying amplitudes add temporal narrative.

Spec Compliance (15/15)

• SC-01: Plot Type (5/5) — Correct mel-spectrogram with mel-scaled frequency axis.
• SC-02: Required Features (4/4) — All spec features present: dB scale ✓, sequential colormap ✓, time axis in seconds ✓, mel-scaled y-axis with Hz labels ✓, colorbar in dB ✓, n_fft=2048 ✓, hop_length=512 ✓, n_mels=128 ✓, synthesized audio ✓.
• SC-03: Data Mapping (3/3) — X=time, Y=mel frequency bands, fill=power in dB. Correct mapping throughout.
• SC-04: Title & Legend (3/3) — Title "spectrogram-mel · plotnine · pyplots.ai" in correct format. Colorbar labeled "Power (dB)".

Data Quality (15/15)

• DQ-01: Feature Coverage (6/6) — Rich signal with fundamental + harmonics, time-varying amplitudes, chirp sweep, and noise. Demonstrates all aspects of mel-spectrogram visualization.
• DQ-02: Realistic Context (5/5) — Audio signal with 220 Hz fundamental and harmonics is a realistic audio analysis scenario. Neutral scientific topic.
• DQ-03: Appropriate Scale (4/4) — 22050 Hz sample rate, 220 Hz fundamental, 3-second duration — all realistic for audio analysis.

Code Quality (10/10)

• CQ-01: KISS Structure (3/3) — Linear flow: imports → data synthesis → STFT → mel filterbank → DataFrame → plot → save. No functions or classes.
• CQ-02: Reproducibility (2/2) — np.random.seed(42) set.
• CQ-03: Clean Imports (2/2) — All imports used. scipy.signal.stft is appropriate.
• CQ-04: Code Elegance (2/2) — Vectorized mel filterbank using numpy broadcasting is clean and efficient. Appropriate complexity for the task.
• CQ-05: Output & API (1/1) — Saves as plot.png with dpi=300.

Library Mastery (6/10)

• LM-01: Idiomatic Usage (4/5) — Good use of ggplot grammar: aes mapping, geom_raster, scale_fill_gradientn, theme layering. Very idiomatic plotnine, though coord_cartesian usage could be more refined.
• LM-02: Distinctive Features (2/5) — geom_raster(interpolate=True) and scale_fill_gradientn are plotnine features, but they're fairly standard. Could leverage more distinctive plotnine features like stat transformations, custom annotation layers, or more advanced scale customization.

Score Caps Applied

• None

Strengths

• Excellent data synthesis with harmonics, chirp sweep, and time-varying amplitudes creating a visually compelling spectrogram
• Manual mel filterbank implementation avoids librosa dependency while remaining clean and vectorized
• Custom inferno gradient with dark panel background creates a cohesive, professional aesthetic
• Full spec compliance — all required features present and correctly implemented
• Perfect code structure following KISS principle

Weaknesses

• Library Mastery could be improved — the implementation uses standard plotnine features without leveraging more distinctive capabilities
• The light gray outer background (#f7f7f7) doesn't fully harmonize with the dark spectrogram panel
• Bottom y-axis labels (64, 128 Hz) are slightly crowded due to mel scale compression

Issues Found

1. LM-02 LOW: Generic plotnine usage without distinctive library features
   • Fix: Consider using plotnine-specific features like annotate() for frequency band labels, or custom geom/stat layers
2. DE-02 MODERATE: Light gray outer background doesn't harmonize with dark spectrogram
   • Fix: Use a darker plot_background or remove the contrast between outer and panel backgrounds
3. VQ-02 MINOR: Bottom y-axis labels (64, 128) crowded
   • Fix: Remove the 64 Hz tick or start y-axis labels at 128 Hz to reduce crowding

AI Feedback for Next Attempt

To reach 90+: (1) Improve library mastery by using plotnine-specific features like annotate() for labeling frequency regions or adding subtle reference lines at key frequencies. (2) Harmonize the outer background with the dark spectrogram — consider a dark or near-black plot_background instead of light gray. (3) Adjust y-axis tick labels to reduce crowding at the bottom — drop the 64 Hz tick or start at 128 Hz. These changes will elevate the design cohesion and demonstrate deeper plotnine expertise.

Verdict: REJECTED

[github-actions]

🔧 Repair Attempt 2/3

Applied fixes based on AI review feedback.

Status: Repair completed, re-triggering review...

---

🤖 impl-repair

[claude]

AI Review - Attempt 3/3

Image Description

The plot displays a mel-spectrogram on a dark background with time (0–3 seconds) on the x-axis and mel-scaled frequency on the y-axis, with Hz labels at key mel band edges (128, 256, 512, 1024, 2048, 4096, 8000 Hz). The colormap is a custom inferno-like gradient progressing from very dark black/purple (low power around -60 dB) through magenta and orange to bright yellow (0 dB). Clear horizontal bands of energy are visible at harmonic frequencies (~220, 440, 880 Hz), with lower harmonics being brightest and decaying over time. A prominent chirp sweep arcs from approximately 500 Hz at t≈0.8s up to ~4000 Hz at t≈2.0s, creating a striking curved bright line that serves as a visual focal point. Annotations label the fundamental frequency ("F₀") and "3rd" harmonic, with subtle reference lines at those frequencies. A colorbar on the right is labeled "Power (dB)" with a tall key. The title reads "spectrogram-mel · plotnine · pyplots.ai" in bold light gray. The panel background is black (#4) matching the colormap floor, and the outer plot background is dark navy (#0e0e1a), creating a cohesive dark theme.

Score: 89/100

Category	Score	Max
Visual Quality	29	30
Design Excellence	15	20
Spec Compliance	15	15
Data Quality	15	15
Code Quality	9	10
Library Mastery	6	10
Total	89	100

Visual Quality (29/30)

• VQ-01: Text Legibility (8/8) — All font sizes explicitly set: title 24pt, axis titles 20pt, ticks 16pt, legend title 16pt, legend text 14pt
• VQ-02: No Overlap (6/6) — All text fully readable, y-axis labels well-spaced on mel scale (128–8000 Hz), annotations positioned to avoid collisions
• VQ-03: Element Visibility (6/6) — geom_raster with interpolate=True produces smooth, gap-free spectrogram rendering; all frequency content clearly visible
• VQ-04: Color Accessibility (4/4) — Custom inferno-like sequential colormap is perceptually uniform and colorblind-safe
• VQ-05: Layout & Canvas (3/4) — Good 16:9 proportions with dark cohesive background; colorbar area takes some canvas space, slight right-side weight
• VQ-06: Axis Labels & Title (2/2) — "Time (s)" and "Frequency (Hz)" with units, correct title format

Design Excellence (15/20)

• DE-01: Aesthetic Sophistication (6/8) — Custom 10-color gradient palette, dark panel matching colormap floor, cohesive dark outer background, styled text color hierarchy (#e0e0e0/#cccccc/#aaaaaa), annotation colors pulled from palette
• DE-02: Visual Refinement (5/6) — Grid completely removed, dark theme throughout, generous legend key (height=60), custom margins; very polished overall
• DE-03: Data Storytelling (4/6) — F₀ and 3rd harmonic annotations guide the viewer, chirp sweep creates natural focal point, subtle reference lines highlight harmonic structure; good visual hierarchy

Spec Compliance (15/15)

• SC-01: Plot Type (5/5) — Correct mel-spectrogram with STFT, mel filterbank, and dB power conversion
• SC-02: Required Features (4/4) — All spec features present: dB scale, sequential colormap, time x-axis in seconds, mel-scaled y-axis with Hz labels, colorbar labeled in dB, n_fft=2048, hop_length=512, n_mels=128, synthesized audio
• SC-03: Data Mapping (3/3) — X=time in seconds, Y=mel frequency bands with Hz labels, fill=power in dB
• SC-04: Title & Legend (3/3) — Correct format "spectrogram-mel · plotnine · pyplots.ai", colorbar labeled "Power (dB)"

Data Quality (15/15)

• DQ-01: Feature Coverage (6/6) — Rich synthesized signal with fundamental (220 Hz), harmonics (440, 880, 1320, 3300 Hz), chirp sweep (500–4000 Hz), noise component, and time-varying amplitudes showing all spectrogram features
• DQ-02: Realistic Context (5/5) — Audio signal with 220 Hz fundamental (A3 note) and natural harmonics is realistic for speech/music analysis
• DQ-03: Appropriate Scale (4/4) — Standard 22050 Hz sample rate, 220 Hz fundamental, 3-second duration, standard STFT parameters

Code Quality (9/10)

• CQ-01: KISS Structure (2/3) — Mostly linear flow but contains a helper function hz_to_band() which slightly breaks the no-functions guideline
• CQ-02: Reproducibility (2/2) — np.random.seed(42) set at top
• CQ-03: Clean Imports (2/2) — All imports used; scipy.signal.stft is an appropriate dependency
• CQ-04: Code Elegance (2/2) — Vectorized mel filterbank using numpy broadcasting is clean and efficient; annotations are legitimate
• CQ-05: Output & API (1/1) — Saves as plot.png with dpi=300, current API

Library Mastery (6/10)

• LM-01: Idiomatic Usage (4/5) — Good ggplot grammar: aes mapping, geom_raster, scale_fill_gradientn, scale_x/y_continuous, coord_cartesian, theme layering, annotate layers
• LM-02: Distinctive Features (2/5) — Uses geom_raster(interpolate=True) and annotate() layers which are plotnine-idiomatic, but these aren't truly distinctive features that couldn't be replicated in other libraries

Score Caps Applied

• None — no caps triggered

Strengths

• Excellent data synthesis with harmonics, chirp sweep, and time-varying amplitudes creating a visually compelling and information-rich spectrogram
• Custom inferno gradient with dark panel/plot backgrounds creates a cohesive, professional dark theme aesthetic
• Manual mel filterbank implementation avoids librosa dependency while remaining clean and vectorized
• Full spec compliance with all required features correctly implemented
• Annotations (F₀, 3rd harmonic) and reference lines add meaningful data storytelling

Weaknesses

• Library Mastery remains the main gap — implementation uses standard plotnine features without leveraging more distinctive capabilities like stat layers or custom geoms
• Small helper function hz_to_band() slightly breaks KISS linear-flow principle

Issues Found

1. CQ-01 MINOR: Helper function hz_to_band() defined in code
   • Fix: Inline the np.interp() calls directly in annotation positions
2. LM-02 LOW: Generic plotnine usage without distinctive library features
   • Fix: Consider using stat transformations or other plotnine-specific grammar features

AI Feedback for Next Attempt

Strong implementation at 89/100. The dark theme, data synthesis, and annotations are excellent. The main gap is Library Mastery (LM-02) — the implementation uses plotnine correctly but generically. To reach 90+, consider leveraging more distinctive plotnine grammar features. The small hz_to_band helper could be inlined for a perfect KISS score.

Verdict: REJECTED

[github-actions]

🔧 Repair Attempt 3/3

Applied fixes based on AI review feedback.

Status: Repair completed, re-triggering review...

---

🤖 impl-repair

[claude]

AI Review - Attempt 3/3

Image Description

The plot displays a mel-spectrogram on a fully dark-themed canvas. The x-axis shows time (0–3 seconds) and the y-axis shows mel-scaled frequency with Hz labels at key mel band edges (128, 256, 512, 1024, 2048, 4096, 8000 Hz). The colormap is a custom inferno-like gradient progressing from very dark black/purple (low power ~-60 dB) through magenta and orange to bright yellow (0 dB). Clear horizontal bands of energy are visible at harmonic frequencies (~220, 440, 880 Hz), with lower harmonics being brightest and decaying over time. A prominent chirp sweep arcs from approximately 500 Hz at t≈0.8s up to ~4000 Hz at t≈2.0s, creating a striking curved bright line that serves as the main visual focal point. Two data-driven annotations label the fundamental frequency ("F₀" in bright yellow) and "3rd" harmonic (in orange), with very subtle reference lines at those frequencies. A tall colorbar on the right is labeled "Power (dB)". The title reads "spectrogram-mel · plotnine · pyplots.ai" in bold light gray. The panel background (#4) matches the colormap floor, and the outer plot background (#0e0e1a) creates a cohesive dark theme throughout.

Score: 90/100

Category	Score	Max
Visual Quality	29	30
Design Excellence	15	20
Spec Compliance	15	15
Data Quality	15	15
Code Quality	10	10
Library Mastery	6	10
Total	90	100

Visual Quality (29/30)

• VQ-01: Text Legibility (8/8) — All font sizes explicitly set: title=24pt, axis titles=20pt, tick labels=16pt, legend title=16pt, legend text=14pt. All perfectly readable on dark background with appropriate contrast colors.
• VQ-02: No Overlap (6/6) — All text fully readable. Y-axis labels well-spaced on mel scale (128–8000 Hz). Annotations positioned at right edge avoiding data collision.
• VQ-03: Element Visibility (6/6) — geom_raster with interpolate=True produces smooth, gap-free spectrogram. Harmonics, chirp sweep, and amplitude decay all clearly visible.
• VQ-04: Color Accessibility (4/4) — Custom inferno-like sequential colormap is perceptually uniform and colorblind-safe. Good contrast throughout.
• VQ-05: Layout & Canvas (3/4) — Good 16:9 proportions. Dark background is cohesive. Plot fills canvas well with tall colorbar. Slight right-side weight from colorbar area.
• VQ-06: Axis Labels & Title (2/2) — "Time (s)" and "Frequency (Hz)" with units. Title in correct format.

Design Excellence (15/20)

• DE-01: Aesthetic Sophistication (6/8) — Custom 10-color gradient palette, dark panel (feat: add complete automation infrastructure for plot generation #4) matching colormap floor, cohesive dark outer background (#0e0e1a), text color hierarchy (#e0e0e0/#cccccc/#aaaaaa), annotation colors pulled from palette endpoints. Clearly above library defaults with intentional design throughout.
• DE-02: Visual Refinement (5/6) — Grid completely removed, dark theme throughout both panel and outer background, generous legend key (height=60, width=14), custom margins. Very polished. Minor: annotation reference lines are extremely subtle (alpha 0.12–0.15), nearly invisible.
• DE-03: Data Storytelling (4/6) — F₀ and 3rd harmonic annotations guide the viewer to harmonic structure. Chirp sweep creates a natural focal point. Time-varying amplitude decay adds temporal narrative. Reference lines provide subtle structural context.

Spec Compliance (15/15)

• SC-01: Plot Type (5/5) — Correct mel-spectrogram with STFT, mel filterbank, and dB power conversion.
• SC-02: Required Features (4/4) — All spec features present: dB scale, sequential colormap, time x-axis in seconds, mel-scaled y-axis with Hz labels at key mel band edges, colorbar labeled in dB, n_fft=2048, hop_length=512, n_mels=128, synthesized audio.
• SC-03: Data Mapping (3/3) — X=time in seconds, Y=mel frequency bands with Hz labels, fill=power in dB. Correct throughout.
• SC-04: Title & Legend (3/3) — Correct format "spectrogram-mel · plotnine · pyplots.ai". Colorbar labeled "Power (dB)".

Data Quality (15/15)

• DQ-01: Feature Coverage (6/6) — Rich synthesized signal with fundamental (220 Hz), harmonics (440, 880, 1320, 3300 Hz), chirp sweep (500–4000 Hz), noise component, and time-varying amplitudes. Demonstrates all aspects of mel-spectrogram visualization.
• DQ-02: Realistic Context (5/5) — Audio signal with 220 Hz fundamental (A3 note) and natural harmonics is realistic for speech/music analysis. Neutral scientific topic.
• DQ-03: Appropriate Scale (4/4) — Standard 22050 Hz sample rate, 3-second duration, standard STFT parameters (n_fft=2048, hop=512). All realistic for audio analysis.

Code Quality (10/10)

• CQ-01: KISS Structure (3/3) — Clean linear flow: imports → data synthesis → STFT → mel filterbank → DataFrame → plot → save. No functions or classes.
• CQ-02: Reproducibility (2/2) — np.random.seed(42) set at top.
• CQ-03: Clean Imports (2/2) — All imports used. scipy.signal.stft is an appropriate dependency for STFT computation.
• CQ-04: Code Elegance (2/2) — Vectorized mel filterbank using numpy broadcasting is clean and efficient. Data-driven annotations via separate DataFrames are elegant.
• CQ-05: Output & API (1/1) — Saves as plot.png with dpi=300, current plotnine API.

Library Mastery (6/10)

• LM-01: Idiomatic Usage (4/5) — Strong grammar-of-graphics composition: aes mapping, geom_raster, scale_fill_gradientn, guide_colorbar(nbin=256, display="raster"), coord_cartesian, extensive theme layering. Data-driven annotations via geom_text/geom_segment with separate DataFrames and inherit_aes=False is the proper ggplot way.
• LM-02: Distinctive Features (2/5) — geom_raster(interpolate=True) and guide_colorbar(nbin=256, display="raster") are plotnine-specific. Data-driven annotation approach with separate DataFrames is idiomatic grammar-of-graphics. However, these aren't features that truly couldn't be replicated in other libraries.

Score Caps Applied

• None — no caps triggered

Strengths

• Cohesive dark theme design with panel background matching colormap floor and harmonized outer background
• Rich synthesized audio data with harmonics, chirp sweep, and amplitude decay creating a visually compelling spectrogram
• Clean vectorized mel filterbank implementation avoiding librosa dependency
• Data-driven annotations using separate DataFrames following grammar-of-graphics principles
• Full spec compliance with all required features correctly implemented

Weaknesses

• Library Mastery remains the main gap — implementation uses plotnine correctly but doesn't leverage truly distinctive features like stat transformations or custom geoms
• Annotation reference lines are extremely subtle (alpha 0.12–0.15), nearly invisible in the final render

Issues Found

1. LM-02 LOW: Plotnine usage is competent and idiomatic but not distinctively leveraging unique library capabilities
   • Fix: Consider stat transformations or other grammar features unique to plotnine/ggplot
2. DE-02 MINOR: Reference line alpha values (0.12, 0.15) are so low they're nearly invisible
   • Fix: Slightly increase alpha to 0.2–0.25 for visibility while maintaining subtlety

AI Feedback for Next Attempt

Implementation reaches publication quality at 90/100. The dark theme cohesion, rich data synthesis, and clean grammar-of-graphics composition are excellent. The main gap is Library Mastery (LM-02) — consider exploring plotnine-specific stat transformations or custom grammar features in future implementations.

Verdict: APPROVED