diff --git a/test/fftspeed.py b/test/fftspeed.py
new file mode 100644
index 0000000..0957f2e
--- /dev/null
+++ b/test/fftspeed.py
@@ -0,0 +1,44 @@
+import numpy
+
+def roundtrip(wave, size):
+    nchan, ntick = wave.shape
+
+    if size == ntick:
+        return wave
+
+    spec = numpy.fft.fft(wave, axis=1)
+    spec = numpy.fft.ifftshift(spec)
+
+    # note: this is not quite right but good enough for speed
+    if size < ntick:            # downsample
+        half = (ntick-size)//2
+        spec = spec[:, half:-half]
+    else:                       # upsample
+        half = (size-ntick)//2
+        spec = numpy.hstack( (numpy.zeros((nchan,half), dtype=spec.dtype),
+                              spec,
+                              numpy.zeros((nchan,half), dtype=spec.dtype)) )
+    spec = numpy.fft.fftshift(spec)
+    wave = numpy.real(numpy.fft.ifft(spec))
+    return wave * wave.shape[1] / ntick
+
+import timeit
+def main(filename, size):
+    f = numpy.load(filename)
+    fr = f[f.files[0]]
+    
+    def runit():
+        roundtrip(fr, size)
+
+    got = timeit.timeit(runit, number=10)
+    print(got)
+
+if '__main__' == __name__:
+    import sys
+    try:
+        size = int(sys.argv[2])
+    except IndexError:
+        size = 6144
+
+    main(sys.argv[1], int(sys.argv[2]))
+