diff --git a/Sources/Butterworth/WaveletsWrapper.mm b/Sources/Butterworth/WaveletsWrapper.mm
index cffb755..dba98ca 100644
--- a/Sources/Butterworth/WaveletsWrapper.mm
+++ b/Sources/Butterworth/WaveletsWrapper.mm
@@ -1,6 +1,6 @@
 //
 //  WaveletsWrapper.cpp
-//  
+//
 //
 //  Created by Nikita Charushnikov on 01.08.23.
 //
@@ -11,7 +11,7 @@
 
 @implementation WaveletsWrapper
 
-- (NSMutableArray<NSNumber *> *)stationaryWaveletTransformation: (double[]) signal :(int) signalSize :(NSString *) wavelet :(int) level {
+- (void)stationaryWaveletTransformation: (double[]) signal :(double[]) result  :(int) signalSize :(NSString *) wavelet :(int) level {
     
     wave_object wave_obj;
     wt_object wavelet_obj;
@@ -26,17 +26,15 @@ @implementation WaveletsWrapper
     
     swt(wavelet_obj, signal);
     
-    NSMutableArray *waveletsOutput = [NSMutableArray array];
-    
     for (int i = 0; i < wavelet_obj->outlength; ++i) {
         const double output = wavelet_obj->output[i];
-        [waveletsOutput addObject:[NSNumber numberWithDouble:output]];
+        result[i] = output;
     }
     
     wave_free(wave_obj);
     wt_free(wavelet_obj);
     
-    return waveletsOutput;
 }
 
 @end
+
diff --git a/Sources/Butterworth/include/WaveletsWrapper.h b/Sources/Butterworth/include/WaveletsWrapper.h
index 6f31133..3db9627 100644
--- a/Sources/Butterworth/include/WaveletsWrapper.h
+++ b/Sources/Butterworth/include/WaveletsWrapper.h
@@ -11,6 +11,6 @@
 
 @interface WaveletsWrapper : NSObject
 
-- (NSMutableArray<NSNumber *> *)stationaryWaveletTransformation: (double[]) signal :(int) signalSize :(NSString *) wavelet :(int) level;
+- (void)stationaryWaveletTransformation: (double[]) signal :(double[]) result  :(int) signalSize :(NSString *) wavelet :(int) level;
 
 @end
diff --git a/Sources/PeakSwift/Utils/Helper/Wavelets/StationaryWaveletTransformation.swift b/Sources/PeakSwift/Utils/Helper/Wavelets/StationaryWaveletTransformation.swift
index 8d10add..db5432f 100644
--- a/Sources/PeakSwift/Utils/Helper/Wavelets/StationaryWaveletTransformation.swift
+++ b/Sources/PeakSwift/Utils/Helper/Wavelets/StationaryWaveletTransformation.swift
@@ -28,12 +28,14 @@ class StationaryWaveletTransformation {
             fatalError("For applying stationary wavelets transformation: signal.size% 2^^level == 0")
         }
         
-        var inputSignal = [Double](signal)
+        let outputWaveletTransformationSize = signalSize * (level + 1)
         
-        let outputWaveletTransformationRaw = waveletsWrapper.stationaryWaveletTransformation(&inputSignal, Int32(signalSize), wavelet.rawValue, Int32(level))
+        var inputSignal = [Double](signal)
+        var outputWaveletTransformation = [Double].init(repeating: 0.0, count: outputWaveletTransformationSize)
         
-        let outputWaveletTransformation = outputWaveletTransformationRaw as! [Double]
+        waveletsWrapper.stationaryWaveletTransformation(&inputSignal, &outputWaveletTransformation, Int32(signalSize), wavelet.rawValue, Int32(level))
         
+       
         return extractCoefficients(waveletOutput: outputWaveletTransformation, level: level)
     }