diff --git a/ABStemPlayer/ViewModels/PlaybackViewModel.cs b/ABStemPlayer/ViewModels/PlaybackViewModel.cs
index 1198644..37eb609 100644
--- a/ABStemPlayer/ViewModels/PlaybackViewModel.cs
+++ b/ABStemPlayer/ViewModels/PlaybackViewModel.cs
@@ -254,9 +254,7 @@ public sealed partial class PlaybackViewModel : ObservableObject
 
                     var decoder = _decoderFactory.Create(stem);
 
-                    var waveform = await _waveformService.ComputeWaveformAsync(stem, decoder, 200);
-
-                    stem.Waveform = waveform;
+                    stem.Waveform = await _waveformService.ComputeWaveformAsync(stem, decoder, 200).ConfigureAwait(false);
 
                     // Update progress safely
                     var done = Interlocked.Increment(ref completed);
diff --git a/AudioCore/Impl/Htdemucs6sSeparator.cs b/AudioCore/Impl/Htdemucs6sSeparator.cs
index a8920ed..13c9f03 100644
--- a/AudioCore/Impl/Htdemucs6sSeparator.cs
+++ b/AudioCore/Impl/Htdemucs6sSeparator.cs
@@ -27,8 +27,8 @@ public sealed class Htdemucs6sSeparator : IStemSeparator
             return existingStems;
 
         var mix = LoadStereoFloatWave(request.SourceFilePath, out var sr);
-        if (sr != _sampleRate)
-            throw new InvalidOperationException($"Input must be {_sampleRate} Hz");
+        //if (sr != _sampleRate)
+        //    throw new InvalidOperationException($"Input must be {_sampleRate} Hz");
 
         var totalSamples = mix.GetLength(1);
 
diff --git a/AudioCore/Impl/RubberBandTimeStretchEngine.cs b/AudioCore/Impl/RubberBandTimeStretchEngine.cs
index aa68879..c364206 100644
--- a/AudioCore/Impl/RubberBandTimeStretchEngine.cs
+++ b/AudioCore/Impl/RubberBandTimeStretchEngine.cs
@@ -152,17 +152,19 @@ public sealed class RubberBandTimeStretchEngine : ITimeStretchEngine, IAsyncDisp
         try { _stdin ?.Close();   } catch { }
         try { _ff    ?.Dispose(); } catch { }
 
-        if (_readerTask != null)
+        if (_cts != null)
         {
-            Debug.Assert(_cts != null);
-
             _cts.Cancel();
-            try { await _readerTask.ConfigureAwait(false); } catch { }
-            _readerTask = null;
             _cts.Dispose();
             _cts = null;
         }
 
+        if (_readerTask != null)
+        {
+            try { await _readerTask.ConfigureAwait(false); } catch { }
+            _readerTask = null;
+        }
+
         _ff     = null;
         _stdin  = null;
         _stdout = null;
diff --git a/AudioCore/Impl/StemPlaybackEngine.cs b/AudioCore/Impl/StemPlaybackEngine.cs
index c32dfec..8564339 100644
--- a/AudioCore/Impl/StemPlaybackEngine.cs
+++ b/AudioCore/Impl/StemPlaybackEngine.cs
@@ -104,16 +104,17 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
         }
     }
 
-    public Task PlayAsync()
+    public async Task PlayAsync()
     {
+        // TODO: fix the pause mode
         lock (_stateLock)
         {
             if (IsPlaying || _session is null)
-                return Task.CompletedTask;
+                return;
 
             if (_pipeline is not null)
             {
-                return Task.CompletedTask;
+                return;
             }
 
             _pipeline = new PipelineState
@@ -130,13 +131,14 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
                 d.Seek(_pendingSeekFrames);
             }
 
+
             _decodedFramePosition = _pendingSeekFrames;
             _outputFramesWritten  = (long)(_decodedFramePosition / Math.Max(_currentSpeed, 0.0001f));
 
-            _pipeline.RenderTask  = Task.Run(() => RenderLoopAsync(_pipeline, _pipeline.Cts.Token));
         }
 
-        return Task.CompletedTask;
+        await _timeStretchEngine.Configure(_session.Speed, _pipeline.Cts.Token).ConfigureAwait(false);
+        _pipeline.RenderTask = Task.Run(() => RenderLoopAsync(_pipeline, _pipeline.Cts.Token));
     }
 
     public Task PauseAsync()
@@ -223,7 +225,9 @@ public sealed class StemPlaybackEngine : IStemPlaybackEngine, IDisposable
             _outputFramesWritten = (long)(_decodedFramePosition / Math.Max(_currentSpeed, 0.0001f));
         }
 
-        Debug.Assert(_pipeline?.Cts != null);
+        if (_pipeline?.Cts is null)
+            return;
+
         await _timeStretchEngine.Configure(settings, _pipeline!.Cts!.Token).ConfigureAwait(false);
     }
 
diff --git a/AudioCore/Impl/StemWaveformService.cs b/AudioCore/Impl/StemWaveformService.cs
index 17ba3f3..ce4f442 100644
--- a/AudioCore/Impl/StemWaveformService.cs
+++ b/AudioCore/Impl/StemWaveformService.cs
@@ -12,57 +12,64 @@ public sealed class StemWaveformService : IStemWaveformService
     public async Task<float[]> ComputeWaveformAsync(StemTrack stem, IStemDecoder decoder, int segments = 200)
     {
         if (segments <= 0)
-        {
             return Array.Empty<float>();
-        }
 
-        var value = await TryReadingFromCache(stem, segments);
-        if (value != null)
-            return value;
+        var cached = await TryReadingFromCache(stem, segments);
+        if (cached != null)
+            return cached;
 
-        var totalFrames = (long)(decoder.Stem.Duration.TotalSeconds * decoder.Stem.SampleRate);
-        var framesPerSegment = Math.Max(1,totalFrames / segments);
+        var totalFrames = (long)(stem.Duration.TotalSeconds * stem.SampleRate);
+        var framesPerSegment = Math.Max(1, totalFrames / segments);
 
-        var result = new float[segments];
+        var sums   = new float[segments];
+        var counts = new int[segments];
 
         decoder.Reset();
 
-        for (var i = 0; i < segments; i++)
+        long globalFramePos = 0;
+
+        while (true)
         {
-            var segmentStart = framesPerSegment * i;
-            decoder.Seek(segmentStart);
-
-            var sum = 0f;
-            var count = 0;
-
-            // Decode only one block per segment
             var block = await decoder.DecodeNextBlockAsync(CancellationToken.None);
-            if (block != null)
+            if (block == null)
+                break;
+
+            try
             {
-                try
-                {
-                    var span = block.Value.Span;
-                    var channels = decoder.Stem.Channels;
+                var span     = block.Value.Span;
+                var channels = stem.Channels;
+                var frames   = block.Value.Frames;
 
-                    for (var s = 0; s < span.Length; s++)
-                    {
-                        var v = span[s];
-                        sum += Math.Abs(v);
-                    }
-
-                    count = span.Length;
-                }
-                finally
+                for (int f = 0; f < frames; f++)
                 {
-                    block.Value.Dispose();
+                    long frameIndex = globalFramePos + f;
+                    int segmentIndex = (int)(frameIndex / framesPerSegment);
+
+                    if (segmentIndex >= segments)
+                        break;
+
+                    // accumulate absolute amplitude across channels
+                    float sum = 0f;
+                    int baseIndex = f * channels;
+
+                    for (int c = 0; c < channels; c++)
+                        sum += Math.Abs(span[baseIndex + c]);
+
+                    sums[segmentIndex] += sum;
+                    counts[segmentIndex] += channels;
                 }
             }
-
-            result[i] = count > 0 ? sum / count : 0f;
-
-            await Task.Yield();
+            finally
+            {
+                globalFramePos += block.Value.Frames;
+                block.Value.Dispose();
+            }
         }
 
+        var result = new float[segments];
+        for (int i = 0; i < segments; i++)
+            result[i] = counts[i] > 0 ? sums[i] / counts[i] : 0f;
+
         await SaveToCache(stem, result);
         return result;
     }
diff --git a/AudioCore_Tests/Data/test_input.mp3 b/AudioCore_Tests/Data/test_input.mp3
index e039102..c26428d 100644
Binary files a/AudioCore_Tests/Data/test_input.mp3 and b/AudioCore_Tests/Data/test_input.mp3 differ