diff --git a/docs/index.rst b/docs/index.rst
index 86af541..4726e2a 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -26,4 +26,5 @@ API Reference
    :maxdepth: 1
    :glob:
 
-   mrs_data_api.rst
+   suspect_api.rst
+   mrs_data_api.rst
\ No newline at end of file
diff --git a/docs/suspect_api.rst b/docs/suspect_api.rst
new file mode 100644
index 0000000..0e12fb5
--- /dev/null
+++ b/docs/suspect_api.rst
@@ -0,0 +1,5 @@
+Suspect API Reference
+=====================
+
+.. automodule:: suspect
+    :members: adjust_phase
diff --git a/suspect/__init__.py b/suspect/__init__.py
index bb1d5fd..659b4c4 100644
--- a/suspect/__init__.py
+++ b/suspect/__init__.py
@@ -7,3 +7,4 @@ from . import fitting
 from . import image
 from . import viz
 from ._version import __version__
+from .core import adjust_phase
diff --git a/suspect/core.py b/suspect/core.py
new file mode 100644
index 0000000..ffbde62
--- /dev/null
+++ b/suspect/core.py
@@ -0,0 +1,25 @@
+from .mrsdata import MRSData
+
+
+def adjust_phase(data, zero_phase, first_phase=0, fixed_frequency=0):
+    """
+    Adjust the phase of an MRSData object
+
+    Parameters
+    ----------
+    data : MRSData
+        The MRSData object to be phased
+    zero_phase : scalar
+        The change to the zero order phase, in radians
+    first_phase : scalar, optional
+        The change to the first order phase, in radians per Hz
+    fixed_frequency : scalar, optional
+        The frequency, in Hz, which is unchanged by the first order
+        phase shift
+
+    Returns
+    -------
+    out : MRSData
+        A new MRSData object with adjusted phase.
+    """
+    return data.adjust_phase(zero_phase, first_phase, fixed_frequency)
diff --git a/suspect/mrsdata.py b/suspect/mrsdata.py
index 0be660d..3d251e7 100644
--- a/suspect/mrsdata.py
+++ b/suspect/mrsdata.py
@@ -246,4 +246,26 @@ class MRSData(numpy.ndarray):
 
         transformed_point = numpy.linalg.inv(self.transform) * numpy.matrix([x, y, z, 1]).T
 
-        return numpy.squeeze(numpy.asarray(transformed_point))[0:3]
\ No newline at end of file
+        return numpy.squeeze(numpy.asarray(transformed_point))[0:3]
+
+    def adjust_phase(self, zero_phase, first_phase=0, fixed_frequency=0):
+        """
+        Adjust the phases of the signal.
+
+        Refer to suspect.adjust_phase for full documentation.
+
+        See Also
+        --------
+        suspect.adjust_phase : equivalent function
+        """
+        # easiest to apply the phase shift in the frequency domain
+        # TODO when MRSSpectrum is a real class, this function can delegate
+        # to that one.
+        spectrum = self.spectrum()
+        phase_ramp = numpy.linspace(-self.sw / 2,
+                                    self.sw / 2,
+                                    self.np,
+                                    endpoint=False)
+        phase_shift = zero_phase + first_phase * (fixed_frequency + phase_ramp)
+        phased_spectrum = spectrum * numpy.exp(1j * phase_shift)
+        return self.inherit(numpy.fft.ifft(numpy.fft.ifftshift(phased_spectrum, axes=-1), axis=-1))

Add adjust_phase function
Add a function which can be passed an MRSData object and a zeroth (and optional first) order phase, and returns a new MRSData object which has had the phase shifts applied. This should also be callable with a method on the original MRSData object, by analogy with methods like np.ndarray.clip()
diff --git a/tests/test_mrs/test_core.py b/tests/test_mrs/test_core.py
new file mode 100644
index 0000000..97a9f0e
--- /dev/null
+++ b/tests/test_mrs/test_core.py
@@ -0,0 +1,17 @@
+import suspect
+
+import numpy
+
+
+def test_adjust_zero_phase():
+    data = suspect.MRSData(numpy.ones(10), 1e-3, 123)
+    phased_data = suspect.adjust_phase(data, numpy.pi / 2)
+    numpy.testing.assert_allclose(phased_data, 1j * numpy.ones(10))
+
+
+def test_adjust_first_phase():
+    data = suspect.MRSData(numpy.fft.ifft(numpy.ones(10)), 1e-1, 123)
+    phased_data = suspect.adjust_phase(data, 0, numpy.pi / 10).spectrum()
+    numpy.testing.assert_almost_equal(phased_data[0], -1j)
+    numpy.testing.assert_almost_equal(phased_data[-1], numpy.exp(1j * 0.4 * numpy.pi))
+    numpy.testing.assert_almost_equal(phased_data[5], 1)

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest mock
3.9
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.16
asteval==1.0.6
asttokens==3.0.0
attrs==25.3.0
babel==2.17.0
beautifulsoup4==4.13.3
bleach==6.2.0
certifi==2025.1.31
charset-normalizer==3.4.1
comm==0.2.2
debugpy==1.8.13
decorator==5.2.1
defusedxml==0.7.1
dill==0.3.9
docutils==0.21.2
exceptiongroup==1.2.2
executing==2.2.0
fastjsonschema==2.21.1
idna==3.10
imagesize==1.4.1
importlib_metadata==8.6.1
iniconfig==2.1.0
ipykernel==6.29.5
ipython==8.18.1
jedi==0.19.2
Jinja2==3.1.6
jsonschema==4.23.0
jsonschema-specifications==2024.10.1
jupyter_client==8.6.3
jupyter_core==5.7.2
jupyterlab_pygments==0.3.0
lmfit==1.3.3
MarkupSafe==3.0.2
matplotlib-inline==0.1.7
mistune==3.1.3
mock==5.2.0
nbclient==0.10.2
nbconvert==7.16.6
nbformat==5.10.4
nbsphinx==0.9.7
nest-asyncio==1.6.0
numpy==2.0.2
packaging==24.2
pandocfilters==1.5.1
Parsley==1.3
parso==0.8.4
pexpect==4.9.0
platformdirs==4.3.7
pluggy==1.5.0
prompt_toolkit==3.0.50
psutil==7.0.0
ptyprocess==0.7.0
pure_eval==0.2.3
pydicom==2.4.4
Pygments==2.19.1
pytest==8.3.5
python-dateutil==2.9.0.post0
PyWavelets==1.6.0
pyzmq==26.3.0
referencing==0.36.2
requests==2.32.3
rpds-py==0.24.0
scipy==1.13.1
six==1.17.0
snowballstemmer==2.2.0
soupsieve==2.6
Sphinx==7.4.7
sphinxcontrib-applehelp==2.0.0
sphinxcontrib-devhelp==2.0.0
sphinxcontrib-htmlhelp==2.1.0
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-qthelp==2.0.0
sphinxcontrib-serializinghtml==2.0.0
stack-data==0.6.3
-e git+https://github.com/openmrslab/suspect.git@973a03f749fd6af336f968dd2e99366586ac59d2#egg=suspect
tinycss2==1.4.0
tomli==2.2.1
tornado==6.4.2
traitlets==5.14.3
typing_extensions==4.13.0
uncertainties==3.2.2
urllib3==2.3.0
wcwidth==0.2.13
webencodings==0.5.1
zipp==3.21.0

name: suspect
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.4.4=h6a678d5_1
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=3.0.16=h5eee18b_0
  - pip=25.0=py39h06a4308_0
  - python=3.9.21=he870216_1
  - readline=8.2=h5eee18b_0
  - setuptools=75.8.0=py39h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - tzdata=2025a=h04d1e81_0
  - wheel=0.45.1=py39h06a4308_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.16
      - asteval==1.0.6
      - asttokens==3.0.0
      - attrs==25.3.0
      - babel==2.17.0
      - beautifulsoup4==4.13.3
      - bleach==6.2.0
      - certifi==2025.1.31
      - charset-normalizer==3.4.1
      - comm==0.2.2
      - debugpy==1.8.13
      - decorator==5.2.1
      - defusedxml==0.7.1
      - dill==0.3.9
      - docutils==0.21.2
      - exceptiongroup==1.2.2
      - executing==2.2.0
      - fastjsonschema==2.21.1
      - idna==3.10
      - imagesize==1.4.1
      - importlib-metadata==8.6.1
      - iniconfig==2.1.0
      - ipykernel==6.29.5
      - ipython==8.18.1
      - jedi==0.19.2
      - jinja2==3.1.6
      - jsonschema==4.23.0
      - jsonschema-specifications==2024.10.1
      - jupyter-client==8.6.3
      - jupyter-core==5.7.2
      - jupyterlab-pygments==0.3.0
      - lmfit==1.3.3
      - markupsafe==3.0.2
      - matplotlib-inline==0.1.7
      - mistune==3.1.3
      - mock==5.2.0
      - nbclient==0.10.2
      - nbconvert==7.16.6
      - nbformat==5.10.4
      - nbsphinx==0.9.7
      - nest-asyncio==1.6.0
      - numpy==2.0.2
      - packaging==24.2
      - pandocfilters==1.5.1
      - parsley==1.3
      - parso==0.8.4
      - pexpect==4.9.0
      - platformdirs==4.3.7
      - pluggy==1.5.0
      - prompt-toolkit==3.0.50
      - psutil==7.0.0
      - ptyprocess==0.7.0
      - pure-eval==0.2.3
      - pydicom==2.4.4
      - pygments==2.19.1
      - pytest==8.3.5
      - python-dateutil==2.9.0.post0
      - pywavelets==1.6.0
      - pyzmq==26.3.0
      - referencing==0.36.2
      - requests==2.32.3
      - rpds-py==0.24.0
      - scipy==1.13.1
      - six==1.17.0
      - snowballstemmer==2.2.0
      - soupsieve==2.6
      - sphinx==7.4.7
      - sphinxcontrib-applehelp==2.0.0
      - sphinxcontrib-devhelp==2.0.0
      - sphinxcontrib-htmlhelp==2.1.0
      - sphinxcontrib-jsmath==1.0.1
      - sphinxcontrib-qthelp==2.0.0
      - sphinxcontrib-serializinghtml==2.0.0
      - stack-data==0.6.3
      - tinycss2==1.4.0
      - tomli==2.2.1
      - tornado==6.4.2
      - traitlets==5.14.3
      - typing-extensions==4.13.0
      - uncertainties==3.2.2
      - urllib3==2.3.0
      - wcwidth==0.2.13
      - webencodings==0.5.1
      - zipp==3.21.0
prefix: /opt/conda/envs/suspect

tests/test_mrs/test_core.py::test_adjust_zero_phase tests/test_mrs/test_core.py::test_adjust_first_phase
docs/suspect_api.rst suspect/core.py suspect/mrsdata.py suspect/__init__.py docs/index.rst
docs/suspect_api.rst suspect/core.py suspect/mrsdata.py suspect/__init__.py docs/index.rst