Gap 4: MaximizerFx oversample 4x soft-clip + ceiling — zero-stuff + FIR33 anti-alias + post-decimation clamp (giảm aliasing fold-back, sample peak <= ceiling); test_61: impulse delay 8 mẫu, unity transparent, alias 9.1k -117dBFS, ceiling -1dB (24 passed)

tests/test_daw_phase5.py

@@ -528,6 +528,85 @@ def test_59_limiter_brickwall_oversample(fx_bridge):
     pk_low = float(np.max(np.abs(out_low)))
     assert 0.05 <= pk_low <= 0.15, f"low-level peak {pk_low:.4f} lech unity"
 
+def test_61_maximizer_oversample(fx_bridge):
+    """Gap 4: MaximizerFx oversample 4x — impulse delay 8 mẫu (2×FIR33 group
+    delay 16@4x / 4) chứng minh oversample active; sine -20dB boost 0 trong
+    suốt (unity); 5kHz soft_clip 100: harmonic 3 (15k) in-band giữ > -40dBFS
+    còn alias spur 9.1k (fold cua harmonic 7 = 35k) bi FIR33 anti-alias chặn
+    < -50dBFS; hot sine bám ceiling -1dB."""
+
+    def _bin_db(x, f):
+        x0 = x[0].astype(np.float64)
+        n = len(x0)
+        win = np.hanning(n)
+        X = np.fft.rfft((x0 - np.mean(x0)) * win)
+        freq = np.fft.rfftfreq(n, 1.0 / SR)
+        i = int(np.argmin(np.abs(freq - f)))
+        amp = np.abs(X[i]) * 2.0 / np.sum(win)
+        return 20.0 * np.log10(amp + 1e-12)
+
+    mx = [{"type": "builtin", "id": "maximizer",
+           "params": {"boost_db": 0.0, "soft_clip": 0.0, "upward": 0.0,
+                      "ceiling_db": -1.0}}]
+    n = 8192
+    t = np.arange(n) / SR
+
+    # 1) impulse → delay 8 (oversample FIR chain active), gain ~1
+    imp = np.zeros(n, dtype=np.float32)
+    imp[512] = 1.0
+    audio = np.stack([imp, imp]).astype(np.float32)
+    with tempfile.TemporaryDirectory() as td:
+        wav_in = os.path.join(td, "in.wav")
+        _write_wav(wav_in, audio, SR)
+        out = _render_bridge(fx_bridge, wav_in, SR, mx, block=512)
+    argmax = int(np.argmax(np.abs(out[0])))
+    assert argmax == 512 + 8, f"impulse delay {argmax - 512} (expect 8)"
+    pk = float(np.max(np.abs(out[0])))
+    assert 0.8 <= pk <= 1.2, f"impulse peak {pk:.4f} (expect ~1.0)"
+
+    # 2) trong suốt: -20dBFS 1kHz qua maximizer gain 0 → unity
+    sine = (0.1 * np.sin(2 * np.pi * 1000.0 * t)).astype(np.float32)
+    audio = np.stack([sine, sine])
+    with tempfile.TemporaryDirectory() as td:
+        wav_in = os.path.join(td, "in.wav")
+        _write_wav(wav_in, audio, SR)
+        out2 = _render_bridge(fx_bridge, wav_in, SR, mx, block=512)
+    pk2 = float(np.max(np.abs(out2[0])))
+    assert 0.09 <= pk2 <= 0.11, f"transparent peak {pk2:.4f} (expect 0.1)"
+
+    # 3) soft_clip 100: 15k in-band giữ, alias 9.1k bị chặn
+    mx_hot = [{"type": "builtin", "id": "maximizer",
+               "params": {"boost_db": 0.0, "soft_clip": 100.0, "upward": 0.0,
+                          "ceiling_db": -1.0}}]
+    sine5 = (0.7 * np.sin(2 * np.pi * 5000.0 * t)).astype(np.float32)
+    audio = np.stack([sine5, sine5])
+    with tempfile.TemporaryDirectory() as td:
+        wav_in = os.path.join(td, "in.wav")
+        _write_wav(wav_in, audio, SR)
+        out3 = _render_bridge(fx_bridge, wav_in, SR, mx_hot, block=512)
+    assert out3.shape == audio.shape, "length giu nguyen"
+    h3 = _bin_db(out3, 15000.0)
+    alias = _bin_db(out3, 9100.0)
+    print(f"maximizer: h3@15k={h3:.1f}dBFS alias@9.1k={alias:.1f}dBFS")
+    assert h3 > -40.0, f"3rd harmonic 15k {h3:.1f}dBFS qua thap"
+    assert alias < -50.0, f"alias spur 9.1k {alias:.1f}dBFS (oversample phai chan fold 35k)"
+
+    # 4) hot sine bám ceiling -1dB
+    ceil_lin = 10.0 ** (-1.0 / 20.0)
+    sine_hot = (0.9 * np.sin(2 * np.pi * 1000.0 * t)).astype(np.float32)
+    audio = np.stack([sine_hot, sine_hot])
+    mx_boost = [{"type": "builtin", "id": "maximizer",
+                 "params": {"boost_db": 18.0, "soft_clip": 100.0, "upward": 0.0,
+                            "ceiling_db": -1.0}}]
+    with tempfile.TemporaryDirectory() as td:
+        wav_in = os.path.join(td, "in.wav")
+        _write_wav(wav_in, audio, SR)
+        out4 = _render_bridge(fx_bridge, wav_in, SR, mx_boost, block=512)
+    pk4 = float(np.max(np.abs(out4[0])))
+    assert pk4 <= ceil_lin + 0.005, f"ceiling peak {pk4:.4f} > {ceil_lin:.4f}"
+    assert pk4 >= 0.7, f"ceiling peak {pk4:.4f} qua thap"
+
+
 # ── 5.C Realtime VST3 setParam live (PLAN_MASTER_ENHANCE C) ───────────────
 def test_60_vst3_setparam_live(fx_bridge, adelay, monkeypatch):
     """set_param runtime cho VST3: chain [vst3-delay, builtin limiter], đổi