diff --git a/huddle-test-geophones/figs/psd_velocity.png b/huddle-test-geophones/figs/psd_velocity.png
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diff --git a/huddle-test-geophones/figs/tf_geophones.png b/huddle-test-geophones/figs/tf_geophones.png
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diff --git a/huddle-test-geophones/index.html b/huddle-test-geophones/index.html
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diff --git a/huddle-test-geophones/index.org b/huddle-test-geophones/index.org
index 90dbf4d..78e2066 100644
--- a/huddle-test-geophones/index.org
+++ b/huddle-test-geophones/index.org
@@ -96,8 +96,8 @@ The voltage amplifiers include a low pass filter with a cut-off frequency at 1kH
 
 ** Compute PSD
 #+begin_src matlab :results none
-  [pxx1, f1] = pwelch(x1, hanning(ceil(length(t)/100)), 0, [], 1/dt);
-  [pxx2, f2] = pwelch(x2, hanning(ceil(length(t)/100)), 0, [], 1/dt);
+  [pxx1, f1] = pwelch(x1, hanning(ceil(1/dt)), 0, [], 1/dt);
+  [pxx2, f2] = pwelch(x2, hanning(ceil(1/dt)), 0, [], 1/dt);
 #+end_src
 
 ** Take into account sensibility of Geophone
@@ -147,6 +147,7 @@ The cut-off frequency is set at 1kHz.
   set(gca, 'xscale', 'log');
   set(gca, 'yscale', 'log');
   xlabel('Frequency [Hz]'); ylabel('PSD [m/s/sqrt(Hz)]')
+  xlim([2, 500]);
 #+end_src
 
 #+NAME: fig:psd_velocity
@@ -159,3 +160,37 @@ The cut-off frequency is set at 1kHz.
 #+CAPTION: Spectral density of the velocity
 #+RESULTS: fig:psd_velocity
 [[file:figs/psd_velocity.png]]
+** Transfer function between the two geophones
+#+begin_src matlab :results none
+  [T12, f12] = tfestimate(x1, x2, hanning(1/dt), 0, [], 1/dt);
+#+end_src
+
+#+begin_src matlab :results none
+  figure;
+  ax1 = subplot(2, 1, 1);
+  plot(f12, abs(T12));
+  set(gca, 'xscale', 'log'); set(gca, 'yscale', 'log');
+  set(gca, 'XTickLabel',[]);
+  ylabel('Magnitude');
+
+  ax2 = subplot(2, 1, 2);
+  plot(f12, mod(180+180/pi*phase(T12), 360)-180);
+  set(gca, 'xscale', 'log');
+  ylim([-180, 180]);
+  yticks([-180, -90, 0, 90, 180]);
+  xlabel('Frequency [Hz]'); ylabel('Phase');
+
+  linkaxes([ax1,ax2],'x');
+  xlim([2, 500]);
+#+end_src
+
+#+NAME: fig:tf_geophones
+#+HEADER: :tangle no :exports results :results value raw replace :noweb yes
+#+begin_src matlab :var filepath="figs/tf_geophones.pdf" :var figsize="full-tall" :post pdf2svg(file=*this*, ext="png")
+  <<plt-matlab>>
+#+end_src
+
+#+NAME: fig:tf_geophones
+#+CAPTION: Estimated transfer function between the two geophones
+#+RESULTS: fig:tf_geophones
+[[file:figs/tf_geophones.png]]