fix: add logarithmic frequency scale to spectrogram matplotlib plots

- Add log_freq parameter to plot_on_axis() and to_matplotlib() (default: True)
- Fixes issue where CQT log-spaced frequency bins were displayed with linear scale
- Sets y-axis to log scale automatically for proper CQT representation

Author: jon-myers

idtap/spectrogram.py

@@ -313,6 +313,7 @@ def plot_on_axis(self, ax: 'Axes',
                     cmap: str = 'viridis',
                     alpha: float = 1.0,
                     zorder: int = 0,
+                    log_freq: bool = True,
                     **imshow_kwargs) -> 'AxesImage':
         """Plot spectrogram on an existing matplotlib axis (for overlays).
 
@@ -325,6 +326,7 @@ def plot_on_axis(self, ax: 'Axes',
             cmap: Matplotlib colormap name
             alpha: Transparency (0.0-1.0), useful for subtle underlays
             zorder: Drawing order (0 = background, higher = foreground)
+            log_freq: Whether to use logarithmic frequency scale (default: True)
             **imshow_kwargs: Additional arguments passed to ax.imshow()
 
         Returns:
@@ -353,6 +355,12 @@ def plot_on_axis(self, ax: 'Axes',
             **imshow_kwargs
         )
 
+        # Set log scale for frequency axis (CQT is log-spaced)
+        if log_freq:
+            ax.set_yscale('log')
+            # Set reasonable y-axis limits
+            ax.set_ylim(self.freq_range[0], self.freq_range[1])
+
         return im
 
     def to_image(self, width: Optional[int] = None,
@@ -417,7 +425,8 @@ def to_matplotlib(self, figsize: Tuple[float, float] = (12, 6),
                      power: float = 1.0,
                      cmap: str = 'viridis',
                      show_colorbar: bool = True,
-                     show_axes: bool = True) -> 'Figure':
+                     show_axes: bool = True,
+                     log_freq: bool = True) -> 'Figure':
         """Generate standalone matplotlib Figure for publication.
 
         Use this for quick visualization. For overlays and custom plots,
@@ -429,6 +438,7 @@ def to_matplotlib(self, figsize: Tuple[float, float] = (12, 6),
             cmap: Matplotlib colormap name
             show_colorbar: Whether to show colorbar
             show_axes: Whether to show frequency/time axis labels
+            log_freq: Whether to use logarithmic frequency scale (default: True)
 
         Returns:
             Matplotlib Figure object
@@ -438,7 +448,7 @@ def to_matplotlib(self, figsize: Tuple[float, float] = (12, 6),
         fig, ax = plt.subplots(figsize=figsize)
 
         # Use plot_on_axis internally
-        im = self.plot_on_axis(ax, power=power, cmap=cmap)
+        im = self.plot_on_axis(ax, power=power, cmap=cmap, log_freq=log_freq)
 
         if show_axes:
             ax.set_xlabel('Time (s)')