diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index f94d1fff62fd3ac81cc77b5fe7d2e2c58595e63a..52e024a4478c103b413275d5487ff16e48892fcc 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,15 +1,7 @@
 # run the test suite
 
-tests_old_ubuntu:
-    image: registry.gitlab.lis-lab.fr:5005/skmad-suite/madarrays/ubuntu:16.04
-    tags:
-        - docker
-    script:
-        - pip3 install . --no-deps
-        - pytest
-
-tests_new_ubuntu:
-    image: registry.gitlab.lis-lab.fr:5005/skmad-suite/madarrays/ubuntu:rolling
+tests:
+    image: registry.gitlab.lis-lab.fr:5005/skmad-suite/madarrays/ubuntu:18.04
     tags:
         - docker
     script:
@@ -20,7 +12,7 @@ tests_new_ubuntu:
 # generate the documentation
 
 pages:
-    image: registry.gitlab.lis-lab.fr:5005/skmad-suite/madarrays/ubuntu:rolling
+    image: registry.gitlab.lis-lab.fr:5005/skmad-suite/madarrays/ubuntu:18.04
     tags:
         - docker
     only:
diff --git a/doc/index.rst b/doc/index.rst
index 274c4cd801be0c415873cfd3555d02a5e4156f26..70dc082975d583dc18abbac2aa5056ea057b8df1 100644
--- a/doc/index.rst
+++ b/doc/index.rst
@@ -26,7 +26,7 @@ Documentation
 .. toctree::
     :maxdepth: 1
 
-    install
+    installation
     references
     tutorials
     credits
diff --git a/doc/install.rst b/doc/installation.rst
similarity index 83%
rename from doc/install.rst
rename to doc/installation.rst
index 3a4659ee5124458ebfa4c481a4b1e95ca2435ea0..40c797c99f2666e4316d432b683c05e8c765dff3 100644
--- a/doc/install.rst
+++ b/doc/installation.rst
@@ -1,24 +1,24 @@
-Install
-#######
+Installation
+############
 
 ``madarrays`` requires the following packages:
 
 * `python >= 3.5 <https://wiki.python.org/moin/BeginnersGuide/Download>`_
-* `numpy >= 1.11 <http://www.numpy.org>`_
-* `scipy >= 0.17 <https://www.scipy.org/scipylib/index.html>`_
-* `matplotlib >= 1.5 <http://matplotlib.org/>`_
+* `numpy >= 1.13 <http://www.numpy.org>`_
+* `scipy >= 0.19 <https://www.scipy.org/scipylib/index.html>`_
+* `matplotlib >= 2.1 <http://matplotlib.org/>`_
 * `simpleaudio >= 1.0 <https://github.com/hamiltron/py-simple-audio>`_
 * `resampy >= 0.2 <https://github.com/bmcfee/resampy>`_
 
-Make sure you Python environment is properly configured. It is recommended to
-install `madarrays` in a virtual environment.
+Make sure your Python environment is properly configured. It is recommended to
+install ``madarrays`` in a virtual environment.
 
 Release version
 ---------------
 
 First, make sure you have the latest version of pip (the Python package
 manager) installed. If you do not, refer to the `Pip documentation
-<https://pip.pypa.io/en/stable/installing/>`_ and install `pip` first.
+<https://pip.pypa.io/en/stable/installing/>`_ and install ``pip`` first.
 
 Install the current release with ``pip``::
 
diff --git a/docker/Dockerfile_ubuntu_16.04 b/docker/Dockerfile_ubuntu_16.04
deleted file mode 100644
index d350c3a6e0d367c582ce878dc9f5174a69322b8e..0000000000000000000000000000000000000000
--- a/docker/Dockerfile_ubuntu_16.04
+++ /dev/null
@@ -1,23 +0,0 @@
-FROM ubuntu:16.04
-MAINTAINER Florent Jaillet
-WORKDIR /
-RUN apt-get update && \
-    apt-get install -y --no-install-recommends \
-        python3 \
-        python3-pip \
-        python3-wheel \
-        python3-setuptools \
-        python3-numpy\
-        python3-scipy \
-        python3-matplotlib \
-        ipython3 \
-        python3-six \
-        python3-dev \
-        gcc \
-        libasound2-dev \
-        && \
-    apt-get clean
-RUN mkdir -p /root/.config/matplotlib && \
-    echo "backend: pdf" > /root/.config/matplotlib/matplotlibrc
-RUN pip3 install llvmlite numba resampy simpleaudio --no-deps
-RUN pip3 install pytest pytest-cov pytest-randomly
diff --git a/docker/Dockerfile_ubuntu_rolling b/docker/Dockerfile_ubuntu_18.04
similarity index 89%
rename from docker/Dockerfile_ubuntu_rolling
rename to docker/Dockerfile_ubuntu_18.04
index eb239840acb6791fac7a09d05d84c5809b3af147..2f0ea8822b774581cec490597c535b616372c12a 100644
--- a/docker/Dockerfile_ubuntu_rolling
+++ b/docker/Dockerfile_ubuntu_18.04
@@ -1,7 +1,9 @@
-FROM ubuntu:rolling
+FROM ubuntu:18.04
 MAINTAINER Florent Jaillet
 WORKDIR /
+ENV DEBIAN_FRONTEND noninteractive
 RUN apt-get update && \
+    apt-get upgrade -y && \
     apt-get install -y --no-install-recommends \
         python3 \
         python3-pip \
@@ -10,6 +12,7 @@ RUN apt-get update && \
         python3-numpy\
         python3-scipy \
         python3-matplotlib \
+        python3-ltfatpy \
         ipython3 \
         python3-six \
         python3-numba \
diff --git a/madarrays/waveform.py b/madarrays/waveform.py
index 08ad2ef04d308d9433c0584339917f515d71902f..15be221dc3da6812cf34b0c384a2fd7a52dcdd72 100644
--- a/madarrays/waveform.py
+++ b/madarrays/waveform.py
@@ -169,7 +169,8 @@ class Waveform(MadArray):
                     raise ValueError(errmsg.format(inputs[0].fs, inputs[1].fs))
 
             output = output.view(Waveform)
-            output.fs = inputs[0].fs if isinstance(inputs[0], Waveform) else inputs[1].fs
+            output.fs = inputs[0].fs if isinstance(inputs[0], Waveform) \
+                else inputs[1].fs
 
         return output
 
@@ -771,7 +772,7 @@ class Waveform(MadArray):
     def copy(self):
         return Waveform(self)
 
-    #  def __add__(self, other):
+    def __add__(self, other):
         if isinstance(other, Waveform) and self.fs != other.fs:
             errmsg = 'Waveforms do not have the same fs: {} and {}'
             raise ValueError(errmsg.format(self.fs, other.fs))
diff --git a/requirements/defaults.txt b/requirements/defaults.txt
index bdfa9d2ce5c4895654a0b39c8b96fb7f8163173a..3e5a679d8d92405bc7b898da39f6b4bd0573cd0d 100644
--- a/requirements/defaults.txt
+++ b/requirements/defaults.txt
@@ -1,7 +1,7 @@
 --index-url https://pypi.python.org/simple/
 
 numpy>=1.13
-scipy>=0.17
-matplotlib>=1.5
+scipy>=0.19
+matplotlib>=2.1
 simpleaudio>=1.0
 resampy>=0.2
diff --git a/setup.py b/setup.py
index 99b2b63ed391e698f3270bb85918b841c281e40f..dd1f49578f0eccf6f1f0d80d1278c13dc7f4c607 100644
--- a/setup.py
+++ b/setup.py
@@ -49,7 +49,7 @@ DESCRIPTION = 'Python package for audio data structures with missing entries'
 LICENSE = 'GNU General Public License v3 (GPLv3)'
 URL = 'https://gitlab.lis-lab.fr/skmad-suite/{}'.format(NAME)
 AUTHOR = 'Ronan Hamon, Valentin Emiya, and Florent Jaillet'
-AUTHOR_EMAIL = ('ronan.hamon@lis-lab.fr', 'valentin.emiya@lis-lab.fr',
+AUTHOR_EMAIL = ('ronan.hamon@lis-lab.fr, valentin.emiya@lis-lab.fr, '
                 'florent.jaillet@lis-lab.fr')
 INSTALL_REQUIRES = ['matplotlib',
                     'numpy',
@@ -71,7 +71,7 @@ CLASSIFIERS = [
     'Programming Language :: Python :: 3.5',
     'Programming Language :: Python :: 3.6']
 PYTHON_REQUIRES = '>=3.5'
-EXTRA_REQUIRE = {
+EXTRAS_REQUIRE = {
     'dev': ['coverage', 'pytest', 'pytest-cov', 'pytest-randomly', 'ipython'],
     'doc': ['sphinx', 'nbsphinx', 'numpydoc', 'sphinx-paramlinks']}
 PROJECT_URLS = {'Bug Reports': URL + '/issues',
@@ -131,7 +131,7 @@ def setup_package():
           packages=find_packages(exclude=['doc', 'dev']),
           install_requires=INSTALL_REQUIRES,
           python_requires=PYTHON_REQUIRES,
-          extras_require=EXTRA_REQUIRE,
+          extras_require=EXTRAS_REQUIRE,
           project_urls=PROJECT_URLS)