Add Lab05 resampling visualization

Author: Lay007

tools/generate_lab05_resampling.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+import numpy as np
+import matplotlib.pyplot as plt
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+OUT = ROOT / "docs" / "assets" / "lab05_resampling_polyphase.png"
+OUT.parent.mkdir(parents=True, exist_ok=True)
+
+fs = 8000
+N = 1024
+t = np.arange(N)/fs
+
+# input signal
+x = np.sin(2*np.pi*700*t) + 0.5*np.sin(2*np.pi*1800*t)
+
+L = 3
+M = 2
+
+# naive upsample
+xu = np.zeros(len(x)*L)
+xu[::L] = x
+
+# simple FIR (low-pass)
+num_taps = 63
+n = np.arange(num_taps) - (num_taps-1)/2
+h = np.sinc(n/L) * np.hanning(num_taps)
+h /= np.sum(h)
+
+xf = np.convolve(xu, h, mode='same')
+
+# decimate
+y = xf[::M]
+
+plt.figure(figsize=(10,6))
+
+plt.subplot(3,1,1)
+plt.plot(x[:200])
+plt.title("Input signal")
+
+plt.subplot(3,1,2)
+plt.plot(xu[:400])
+plt.title("Upsampled (zero insertion)")
+
+plt.subplot(3,1,3)
+plt.plot(y[:200])
+plt.title("Resampled output (L/M)")
+
+plt.tight_layout()
+plt.savefig(OUT, dpi=150)
+print("Saved:", OUT)