From 39cc670cd23478621b44b783c141c2139ceb44f2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20=C4=8Colja?= <martin.colja@infinum.com>
Date: Fri, 1 Mar 2024 13:00:58 +0100
Subject: [PATCH 1/2] write failing test

---
 .../AudioKitEXTests/CallbackInstrumentTests.swift | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Tests/AudioKitEXTests/CallbackInstrumentTests.swift b/Tests/AudioKitEXTests/CallbackInstrumentTests.swift
index 5bf1019..80741b1 100644
--- a/Tests/AudioKitEXTests/CallbackInstrumentTests.swift
+++ b/Tests/AudioKitEXTests/CallbackInstrumentTests.swift
@@ -66,5 +66,20 @@ class CallbackInstrumentTests: XCTestCase {
         /// If the callback does get called, this will fail our test, adding insult to injury
         XCTAssertEqual(data, expectedData)
     }
+
+    func testClearsBuffer() {
+        let input = PlaygroundOscillator(waveform: Table([1, 1]))
+        let callback = CallbackInstrument()
+
+        let engine = AudioEngine()
+        let mixer = Mixer(input, callback)
+        engine.output = mixer
+
+        input.start()
+        let audio = engine.startTest(totalDuration: 1.0)
+        audio.append(engine.render(duration: 1.0))
+
+        XCTAssertTrue(audio.toFloatChannelData()!.flatMap { $0 }.allSatisfy { $0 == 1 })
+    }
 }
 #endif

From 729719cdda2e7100b813ca3cb1ab82a505eb07e4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20=C4=8Colja?= <martin.colja@infinum.com>
Date: Fri, 1 Mar 2024 13:01:33 +0100
Subject: [PATCH 2/2] set output buffer values to zero

---
 Sources/CAudioKitEX/Nodes/CallbackInstrumentDSP.mm | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Sources/CAudioKitEX/Nodes/CallbackInstrumentDSP.mm b/Sources/CAudioKitEX/Nodes/CallbackInstrumentDSP.mm
index 3054a84..98635ef 100644
--- a/Sources/CAudioKitEX/Nodes/CallbackInstrumentDSP.mm
+++ b/Sources/CAudioKitEX/Nodes/CallbackInstrumentDSP.mm
@@ -36,6 +36,8 @@
     }
 
     void process(FrameRange range) override {
+        zeroOutput(range.count, range.start);
+
         count += range.count;
         if (updateTime) {
             lastFrameCount = count;