diff --git a/dont_fret/channel_kde.py b/dont_fret/channel_kde.py
new file mode 100644
index 0000000..fac0a3a
--- /dev/null
+++ b/dont_fret/channel_kde.py
@@ -0,0 +1,142 @@
+"""
+Module for channel based kernel density estimation
+
+This is based on:
+Disentangling Subpopulations in Single-Molecule FRET and ALEX Experiments with Photon Distribution Analysis
+https://doi.org/10.1016/j.bpj.2011.11.4025
+
+Please cite the paper when using this module.
+
+"""
+
+import warnings
+from typing import Optional
+
+import numpy as np
+import polars as pl
+from numba import float64, int64, jit, types
+
+from dont_fret.expr import is_in_expr
+
+
+def alex_2cde(
+    burst_photons: pl.DataFrame,
+    kde_rates: pl.DataFrame,
+    dex_streams: Optional[list[str]] = None,
+    aex_streams: Optional[list[str]] = None,
+) -> pl.Series:
+    """
+    burst_photons: Dataframe with columns: timestamps, stream, burst_index
+    kde_rates: Dataframe with columns: timestamps, D_ex, A_ex.
+    dex_streams: list of photon streams which are donor excitation (default: DD, DA)
+    aex_streams: list of photon streams which are acceptor excitation (default: AA)
+    """
+    dex_streams = dex_streams if dex_streams else ["DD", "DA"]
+    aex_streams = aex_streams if aex_streams else ["AA"]
+
+    f_dex = is_in_expr("stream", dex_streams)
+    f_aex = is_in_expr("stream", aex_streams)
+
+    # equivalent to (but faster):
+    # joined_df = burst_photons.join(kde_rates, on=['timestamps', 'stream'], how='inner')
+    j1 = burst_photons.join(kde_rates, on=["timestamps"], how="left")
+    joined_df = j1.filter(pl.col("stream") == pl.col("stream_right"))
+    # joined_df = burst_photons.join(kde_rates, on=["timestamps"], how="left").filter(
+    #     pl.col("stream") == pl.col("stream_right")
+    # )
+
+    b_df = joined_df.select(
+        [
+            pl.col("burst_index"),
+            pl.col("stream"),
+            (pl.col("A_ex") / pl.col("D_ex")).alias("ratio_AD"),
+        ]
+    )
+
+    # tomov et al eqn 10 and 11
+    df_f_dex = b_df.filter(f_dex)
+    agg_dex = df_f_dex.group_by("burst_index", maintain_order=True).agg(
+        [pl.col("ratio_AD").sum(), pl.len().alias("N_dex")]
+    )
+
+    df_f_aex = b_df.filter(f_aex)
+    agg_dax = df_f_aex.group_by("burst_index", maintain_order=True).agg(
+        [(1 / pl.col("ratio_AD")).sum().alias("ratio_DA"), pl.len().alias("N_aex")]
+    )
+
+    combined = pl.concat([agg_dex, agg_dax], how="align")
+
+    # tomov et al eqn 12
+    ax_2cde_bracket = (1 / pl.col("N_aex")) * pl.col("ratio_AD") - (1 / pl.col("N_dex")) * pl.col(
+        "ratio_DA"
+    )
+    ax_2cde_norm = pl.lit(100) - pl.lit(50) * ax_2cde_bracket
+
+    alex_2cde = combined.select(ax_2cde_norm.alias("alex_2cde")).to_series()
+
+    return alex_2cde
+
+
+def make_kernel(
+    tau: float, timestamps_unit: float, domain_size: int = 10, kernel="laplace"
+) -> np.ndarray:
+    window_size = domain_size * (tau / timestamps_unit)
+    window_size_even_int = 2 * round(window_size / 2)
+
+    # check that rounding error isnt too large
+    rel_dev = (window_size - window_size_even_int) / window_size
+    if np.abs(rel_dev) > 0.01:
+        warnings.warn(
+            "Kernel window size deviation from rounding larger than 1 percent. Choose a smaller `tau` with respect to `timestamps_unit'"
+        )
+
+    t_eval = np.linspace(-domain_size / 2, domain_size / 2, window_size_even_int + 1, endpoint=True)
+    kernel = np.exp(-np.abs(t_eval))
+
+    return kernel
+
+
+def convolve_stream(data: pl.DataFrame, streams: list[str], kernel: np.ndarray) -> np.ndarray:
+    f_expr = is_in_expr("stream", streams)
+
+    df = data.filter(f_expr)
+    # TODO warn on copy
+    event_times = df["timestamps"].to_numpy(allow_copy=True)
+    eval_times = data["timestamps"].to_numpy(allow_copy=True)
+
+    return async_convolve(event_times, eval_times, kernel)
+
+
+@jit(
+    float64[:](
+        types.Array(int64, 1, "C", readonly=True),
+        types.Array(int64, 1, "C", readonly=True),
+        types.Array(float64, 1, "C", readonly=True),
+    ),
+    nopython=True,
+    cache=True,
+    nogil=True,
+)
+def async_convolve(event_times, eval_times, kernel):
+    """convolve integer timestamps with a kernel"""
+
+    i_lower = 0
+    i_upper = 0
+
+    window_half_size = len(kernel) // 2
+    result = np.zeros_like(eval_times, dtype=np.float64)
+
+    for i, time in enumerate(eval_times):
+        while event_times[i_upper] < time + window_half_size:
+            if i_upper == len(event_times):
+                break
+            i_upper += 1
+
+        while event_times[i_lower] < time - window_half_size:
+            i_lower += 1
+
+        for j in range(i_lower, i_upper):
+            idx = event_times[j] - time + window_half_size
+            result[i] += kernel[idx]
+
+    return result
diff --git a/dont_fret/expr.py b/dont_fret/expr.py
index 123dc07..a175424 100644
--- a/dont_fret/expr.py
+++ b/dont_fret/expr.py
@@ -32,6 +32,17 @@ def reduce_or(exprs: list[pl.Expr]) -> pl.Expr:
     return reduce(or_, exprs)
 
 
+def is_in_expr(field: str, values: list) -> pl.Expr:
+    """generate an polars expression equivalent to pl.col(field).is_in(values) by chaining equal
+    and or operations together
+
+    this is (sometimes?) faster to execute
+    """
+
+    exprs = [pl.col(field) == value for value in values]
+    return reduce_or(exprs)
+
+
 def parse_yaml_expressions(yaml_content: str) -> Dict[str, pl.Expr]:
     yaml_data = yaml.safe_load(yaml_content)
     return {key: parse_expression(value).alias(key) for key, value in yaml_data.items()}
diff --git a/templates/07_c_kde.py b/templates/07_c_kde.py
new file mode 100644
index 0000000..b3693a1
--- /dev/null
+++ b/templates/07_c_kde.py
@@ -0,0 +1,43 @@
+# %%
+from pathlib import Path
+
+import matplotlib.pyplot as plt
+import polars as pl
+
+from dont_fret.channel_kde import alex_2cde, convolve_stream, make_kernel
+from dont_fret.fileIO import PhotonFile
+from dont_fret.models import PhotonData
+
+# %%
+cwd = Path(__file__).parent
+test_data_dir = cwd.parent / "tests" / "test_data" / "input" / "ds1"
+ptu_file = "datafile_1.ptu"
+
+# %%
+photons = PhotonData.from_file(PhotonFile(test_data_dir / ptu_file))
+
+tau = 50e-6
+assert photons.timestamps_unit
+kernel = make_kernel(tau, photons.timestamps_unit)
+
+fig, ax = plt.subplots()
+ax.plot(kernel)
+
+# %%
+
+# tomov et al eqn 9
+D_ex = convolve_stream(photons.data, ["DD", "DA"], kernel)
+A_ex = convolve_stream(photons.data, ["AA"], kernel)
+
+# %%
+
+kde_data = photons.data.select(
+    [pl.col("timestamps"), pl.col("stream"), pl.lit(D_ex).alias("D_ex"), pl.lit(A_ex).alias("A_ex")]
+)
+
+bursts = photons.burst_search("APBS")
+
+# %%
+alex_2cde_vals = alex_2cde(bursts.photon_data, kde_data)
+
+# %%
diff --git a/tests/generate_fretbursts_kde.py b/tests/generate_fretbursts_kde.py
new file mode 100644
index 0000000..e6dc9a1
--- /dev/null
+++ b/tests/generate_fretbursts_kde.py
@@ -0,0 +1,114 @@
+"""
+generates test data for comparing fretbursts / dontfret channel kde
+
+ran with fretbursts '0.8.3'
+
+"""
+# %%
+
+import polars as pl
+from fretbursts import *
+from fretbursts.phtools import phrates
+
+# %%
+
+
+url = "http://files.figshare.com/2182601/0023uLRpitc_NTP_20dT_0.5GndCl.hdf5"
+download_file(url, save_dir="./data")
+
+filename = "data/0023uLRpitc_NTP_20dT_0.5GndCl.hdf5"
+
+d = loader.photon_hdf5(filename)
+loader.alex_apply_period(d)
+d.calc_bg(fun=bg.exp_fit, time_s=20, tail_min_us="auto", F_bg=1.7)
+d.burst_search()
+
+ds1 = d.select_bursts(select_bursts.size, th1=30)
+ds = ds1.select_bursts(select_bursts.naa, th1=30)
+
+# %%
+ph = d.ph_times_m[0]
+
+
+tau_s = 50e-6  # in seconds
+tau = int(tau_s / d.clk_p)  # in raw timestamp units
+tau
+
+# %%
+
+# %%
+bursts = ds1.mburst[0]
+
+ph_dex = d.get_ph_times(ph_sel=Ph_sel(Dex="DAem"))
+ph_aex = d.get_ph_times(ph_sel=Ph_sel(Aex="Aem"))
+
+mask_dex = d.get_ph_mask(ph_sel=Ph_sel(Dex="DAem"))
+mask_aex = d.get_ph_mask(ph_sel=Ph_sel(Aex="Aem"))
+
+KDE_DexTi = phrates.kde_laplace(ph_dex, tau, time_axis=ph)
+KDE_AexTi = phrates.kde_laplace(ph_aex, tau, time_axis=ph)
+
+# %%
+
+
+# %%
+
+ALEX_2CDE = []
+BRDex, BRAex = [], []
+for ib, burst in enumerate(bursts):
+    burst_slice = slice(int(burst.istart), int(burst.istop) + 1)
+    if ~mask_dex[burst_slice].any() or ~mask_aex[burst_slice].any():
+        # Either D or A photon stream has no photons in current burst,
+        # thus ALEX_2CDE cannot be computed.
+        ALEX_2CDE.append(np.nan)
+        continue
+
+    kde_dexdex = KDE_DexTi[burst_slice][mask_dex[burst_slice]]
+    kde_aexdex = KDE_AexTi[burst_slice][mask_dex[burst_slice]]
+    N_chaex = mask_aex[burst_slice].sum()
+    BRDex.append(np.sum(kde_aexdex / kde_dexdex) / N_chaex)
+
+    kde_aexaex = KDE_AexTi[burst_slice][mask_aex[burst_slice]]
+    kde_dexaex = KDE_DexTi[burst_slice][mask_aex[burst_slice]]
+    N_chdex = mask_dex[burst_slice].sum()
+    BRAex.append(np.sum(kde_dexaex / kde_aexaex) / N_chdex)
+
+    alex_2cde = 100 - 50 * (BRDex[-1] - BRAex[-1])
+    ALEX_2CDE.append(alex_2cde)
+ALEX_2CDE = np.array(ALEX_2CDE)
+
+ALEX_2CDE
+
+# %%
+
+timestamps = ph
+timestamps
+# %%
+
+stream = np.empty_like(timestamps, dtype="U2")
+stream
+
+
+streams = {
+    "DD": {"Dex": "Dem"},
+    "DA": {"Dex": "Aem"},
+    "AA": {"Aex": "Aem"},
+    "AD": {"Aex": "Dem"},
+}
+
+for stream_label, kwargs in streams.items():
+    mask = d.get_ph_mask(ph_sel=Ph_sel(**kwargs))
+    stream[mask] = stream_label
+
+# %%
+
+
+photons_export = pl.DataFrame({"timestamps": timestamps, "stream": stream})
+photons_export.write_parquet("photon_data.pq")
+
+# %%
+
+
+burst_export = pl.DataFrame([{"istart": b.istart, "istop": b.istop} for b in bursts])
+burst_export = burst_export.with_columns(pl.lit(ALEX_2CDE).alias("alex_2cde"))
+burst_export.write_parquet("burst_data.pq")
diff --git a/tests/test_c_kde.py b/tests/test_c_kde.py
new file mode 100644
index 0000000..7300ba2
--- /dev/null
+++ b/tests/test_c_kde.py
@@ -0,0 +1,48 @@
+# %%
+
+from pathlib import Path
+
+import matplotlib.pyplot as plt
+import numpy as np
+import polars as pl
+import polars.testing as pl_test
+
+from dont_fret.channel_kde import alex_2cde, convolve_stream, make_kernel
+from dont_fret.fileIO import PhotonFile
+from dont_fret.models import PhotonData
+
+cwd = Path(__file__).parent
+input_data_dir = cwd / "test_data" / "input"
+output_data_dir = cwd / "test_data" / "output"
+
+
+def test_compare_cde_fretbursts():
+    tau = 50e-6
+    TIMESTAMPS_UNIT = 1.25e-08
+
+    photon_data = pl.read_parquet(output_data_dir / "kde" / "photon_data.pq")
+    bursts_ref = pl.read_parquet(output_data_dir / "kde" / "burst_data.pq")
+
+    kernel = make_kernel(tau, TIMESTAMPS_UNIT)
+    D_ex = convolve_stream(photon_data, ["DD", "DA"], kernel)
+    A_ex = convolve_stream(photon_data, ["AA"], kernel)
+    kde_data = photon_data.select(
+        [
+            pl.col("timestamps"),
+            pl.col("stream"),
+            pl.lit(D_ex).alias("D_ex"),
+            pl.lit(A_ex).alias("A_ex"),
+        ]
+    )
+
+    burst_dfs = []
+    for i in range(len(bursts_ref)):
+        istart = bursts_ref[i]["istart"].item()
+        istop = bursts_ref[i]["istop"].item()
+        b_df = photon_data[istart : istop + 1].with_columns(pl.lit(i).alias("burst_index"))
+        burst_dfs.append(b_df)
+
+    burst_data = pl.concat(burst_dfs, how="vertical_relaxed")
+
+    alex_2cde_vals = alex_2cde(burst_data, kde_data)
+    pl_test.assert_series_equal(alex_2cde_vals.fill_null(np.nan), bursts_ref["alex_2cde"])
diff --git a/tests/test_data/output/kde/burst_data.pq b/tests/test_data/output/kde/burst_data.pq
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index 0000000..e7bad89
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diff --git a/tests/test_data/output/kde/photon_data.pq b/tests/test_data/output/kde/photon_data.pq
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index 0000000..139f93b
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