diff --git a/app/common/audio/audio.go b/app/common/audio/audio.go
index cffc24a..af9d663 100644
--- a/app/common/audio/audio.go
+++ b/app/common/audio/audio.go
@@ -39,74 +39,80 @@ func CombineWAVFiles(dirPath, outputFilename string, pauseDuration time.Duration
 	}
 
 	for index, wavPath := range wavFiles {
-		file, err := os.Open(wavPath)
-		defer file.Close()
-		if err != nil {
-			return err
-		}
-
-		decoder := wav.NewDecoder(file)
-		if !decoder.IsValidFile() {
-			return response.Err(fmt.Errorf("Invalid WAV file: " + wavPath))
-		}
+		if err := func() error {
+			file, err := os.Open(wavPath)
+			if err != nil {
+				return err
+			}
+			defer file.Close()
 
-		pcmBuffer, err := decoder.FullPCMBuffer()
-		if err != nil {
-			return response.Err(err)
-		}
+			decoder := wav.NewDecoder(file)
+			if !decoder.IsValidFile() {
+				return response.Err(fmt.Errorf("Invalid WAV file: " + wavPath))
+			}
 
-		if pcmBuffer.Format.SampleRate != sampleRate {
-			pcmBuffer, err = ResampleBuffer(pcmBuffer, sampleRate)
+			pcmBuffer, err := decoder.FullPCMBuffer()
 			if err != nil {
-				response.Err(err)
+				return response.Err(err)
 			}
-		}
 
-		if pcmBuffer.Format.NumChannels != channelCount {
-			pcmBuffer, err = ChangeChannelCount(pcmBuffer, channelCount)
-			if err != nil {
-				response.Err(err)
+			if pcmBuffer.Format.SampleRate != sampleRate {
+				pcmBuffer, err = ResampleBuffer(pcmBuffer, sampleRate)
+				if err != nil {
+					return response.Err(err)
+				}
 			}
-		}
 
-		if pcmBuffer.SourceBitDepth != bitDepth {
-			pcmBuffer, err = ChangeBitDepth(pcmBuffer, bitDepth)
-			if err != nil {
-				response.Err(err)
+			if pcmBuffer.Format.NumChannels != channelCount {
+				pcmBuffer, err = ChangeChannelCount(pcmBuffer, channelCount)
+				if err != nil {
+					return response.Err(err)
+				}
 			}
-		}
 
-		if index == 0 {
-			combinedBuffer = &audio.IntBuffer{
-				Data:           []int{},
-				Format:         pcmBuffer.Format,
-				SourceBitDepth: pcmBuffer.SourceBitDepth,
+			if pcmBuffer.SourceBitDepth != bitDepth {
+				pcmBuffer, err = ChangeBitDepth(pcmBuffer, bitDepth)
+				if err != nil {
+					return response.Err(err)
+				}
 			}
-		}
 
-		combinedBuffer.Data = append(combinedBuffer.Data, pcmBuffer.Data...)
+			if index == 0 {
+				combinedBuffer = &audio.IntBuffer{
+					Data:           []int{},
+					Format:         pcmBuffer.Format,
+					SourceBitDepth: pcmBuffer.SourceBitDepth,
+				}
+			}
 
-		if index < len(wavFiles)-1 {
-			combinedBuffer.Data = append(combinedBuffer.Data, silenceBuffer.Data...)
+			combinedBuffer.Data = append(combinedBuffer.Data, pcmBuffer.Data...)
+
+			if index < len(wavFiles)-1 {
+				combinedBuffer.Data = append(combinedBuffer.Data, silenceBuffer.Data...)
+			}
+
+			return nil
+		}(); err != nil {
+			return err
 		}
 	}
 
 	outputPath := filepath.Join(dirPath, outputFilename)
 	combinedFile, err := os.Create(outputPath)
 	if err != nil {
-		response.Err(err)
+		return response.Err(err)
 	}
 	defer combinedFile.Close()
 
 	encoder := wav.NewEncoder(combinedFile, sampleRate, bitDepth, channelCount, 1)
 	err = encoder.Write(combinedBuffer)
 	if err != nil {
-		response.Err(err)
+		return response.Err(err)
 	}
 
 	err = encoder.Close()
 	if err != nil {
-		response.Err(err)
+		return response.Err(err)
 	}
 
 	return nil
diff --git a/app/common/audio/player/player.go b/app/common/audio/player/player.go
index 97a5344..a2dddf7 100644
--- a/app/common/audio/player/player.go
+++ b/app/common/audio/player/player.go
@@ -5,6 +5,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/gopxl/beep"
@@ -15,6 +16,10 @@ import (
 	"github.com/gopxl/beep/wav"
 )
 
+const targetRate = beep.SampleRate(48000)
+
+var speakerInitOnce sync.Once
+
 func PlayAudioFile(filePath string) error {
 	if _, err := os.Stat(filePath); os.IsNotExist(err) {
 		return fmt.Errorf("file not found: %s", filePath)
@@ -48,8 +53,9 @@ func PlayAudioFile(filePath string) error {
 	}
 	defer streamer.Close()
 
-	targetRate := beep.SampleRate(48000)
-	speaker.Init(targetRate, targetRate.N(time.Second/10))
+	speakerInitOnce.Do(func() {
+		speaker.Init(targetRate, targetRate.N(time.Second/10))
+	})
 
 	var finalStreamer beep.Streamer = streamer
 	if format.SampleRate != targetRate {