diff --git a/downsampled_audio.wav b/downsampled_audio.wav
new file mode 100644
index 0000000..854b8e5
Binary files /dev/null and b/downsampled_audio.wav differ
diff --git a/speech_analysis.m b/speech_analysis.m
index d93cb2d..be5ebb5 100644
--- a/speech_analysis.m
+++ b/speech_analysis.m
@@ -1,17 +1,16 @@
 pkg load signal
 
 %load & plot audio file modulator
-%modulator = fullfile('sound', 'modulator22.wav');
 [audio_data sampling_freq]= audioread('modulator22.wav');
 
 figure;
 plot(audio_data);
-xlabel('Time (s)');
-ylabel('Amplitude');
-title('Modulator22');
+xlabel('Time in [s]');
+ylabel('Amplitude in [dB]');
+title('Speech data in time domain');
 
-%spectral anlysis
-if (1)
+%FFT vs DFT comparison
+if (0)
   t = 5;
   %average
   for i=1:t
@@ -38,11 +37,13 @@ average_fft = sum_fft/t
 average_dft = sum_dft/t
 end
 
+%Spectrogram
+frequencySpectrum(audio_data,sampling_freq,1);
+
 %Compute and display spectrogram
 if(0)
   spectrogram(audio_data,sampling_freq,5,5);
   %spectrogram(audio_data,sampling_freq,30,5);
-
   wan = audio_data(0.37*sampling_freq:1.17*sampling_freq);
   tu = audio_data(1.24*sampling_freq:1.75*sampling_freq);
   tri = audio_data(1.84*sampling_freq:2.19*sampling_freq);
@@ -50,4 +51,20 @@ if(0)
   frequencySpectrum(wan,sampling_freq,1);
   frequencySpectrum(tu,sampling_freq,1);
   frequencySpectrum(tri,sampling_freq,1);
-end
\ No newline at end of file
+end
+
+%downsampling
+audio_downsampled = downsample(audio_data, 2);
+audiowrite('downsampled_audio.wav',audio_downsampled ,4000);
+
+%down_deci = decimate(audio_data, 2);
+%audiowrite('decimate_audio.wav',down_deci,4000);
+
+%low-pass filter
+lp = fir1(30,1000/sampling_freq,'low');
+y = filter(lp,1,audio_data);
+frequencySpectrum(y,sampling_freq,1);
+
+lp_butter = butter(8,1000/sampling_freq,'low');
+y_butter = filter(lp_butter,1,audio_data);
+frequencySpectrum(y_butter,sampling_freq,1);
\ No newline at end of file