diff --git a/mhkit/acoustics/analysis.py b/mhkit/acoustics/analysis.py
index 145757fd..80e9030a 100644
--- a/mhkit/acoustics/analysis.py
+++ b/mhkit/acoustics/analysis.py
@@ -50,6 +50,17 @@
 from mhkit.dolfyn.time import epoch2dt64, dt642epoch
 
 
+def _check_numeric(value, name: str):
+    if np.issubdtype(type(value), np.ndarray):
+        value = value.item()
+    if not (
+        isinstance(value, (int, float))
+        or np.issubdtype(type(value), np.integer)
+        or np.issubdtype(type(value), np.floating)
+    ):
+        raise TypeError(f"{name} must be a numeric type (int or float).")
+
+
 def _fmax_warning(
     fn: Union[int, float, np.ndarray], fmax: Union[int, float, np.ndarray]
 ) -> Union[int, float, np.ndarray]:
@@ -69,11 +80,6 @@ def _fmax_warning(
         The adjusted maximum frequency limit, ensuring it does not exceed the Nyquist frequency.
     """
 
-    if not isinstance(fn, (int, float, np.ndarray)):
-        raise TypeError("'fn' must be a numeric type (int or float).")
-    if not isinstance(fmax, (int, float, np.ndarray)):
-        raise TypeError("'fmax' must be a numeric type (int or float).")
-
     if fmax > fn:
         warnings.warn(
             f"`fmax` = {fmax} is greater than the Nyquist frequency. Setting"
@@ -120,10 +126,8 @@ def minimum_frequency(
     if not np.issubdtype(water_depth.dtype, np.number):
         raise TypeError("'water_depth' must be a numeric type or array of numerics.")
 
-    if not isinstance(c, (int, float)):
-        raise TypeError("'c' must be a numeric type (int or float).")
-    if not isinstance(c_seabed, (int, float)):
-        raise TypeError("'c_seabed' must be a numeric type (int or float).")
+    _check_numeric(c, "c")
+    _check_numeric(c_seabed, "c_seabed")
 
     if np.any(water_depth <= 0):
         raise ValueError("All elements of 'water_depth' must be positive numbers.")
@@ -143,6 +147,7 @@ def sound_pressure_spectral_density(
     pressure: xr.DataArray,
     fs: Union[int, float],
     bin_length: Union[int, float] = 1,
+    fft_length: Optional[Union[int, float]] = None,
     rms: bool = True,
 ) -> xr.DataArray:
     """
@@ -167,6 +172,8 @@ def sound_pressure_spectral_density(
         Data collection sampling rate [Hz]
     bin_length: int or float
         Length of time in seconds to create FFTs. Default: 1.
+    fft_length: int or float, optional
+        Length of FFT to use. If None, uses bin_length * fs. Default: None.
     rms: bool
         If True, calculates the mean-squared SPSD. Set to False to
         calculate standard SPSD. Default: True.
@@ -180,10 +187,8 @@ def sound_pressure_spectral_density(
     # Type checks
     if not isinstance(pressure, xr.DataArray):
         raise TypeError("'pressure' must be an xarray.DataArray.")
-    if not isinstance(fs, (int, float)):
-        raise TypeError("'fs' must be a numeric type (int or float).")
-    if not isinstance(bin_length, (int, float)):
-        raise TypeError("'bin_length' must be a numeric type (int or float).")
+    _check_numeric(fs, "fs")
+    _check_numeric(bin_length, "bin_length")
 
     # Ensure that 'pressure' has a 'time' coordinate
     if "time" not in pressure.dims:
@@ -191,9 +196,14 @@ def sound_pressure_spectral_density(
 
     # window length of each time series
     nbin = bin_length * fs
+    if fft_length is not None:
+        _check_numeric(fft_length, "fft_length")
+        nfft = fft_length
+    else:
+        nfft = nbin
 
     # Use dolfyn PSD functionality
-    binner = VelBinner(n_bin=nbin, fs=fs, n_fft=nbin)
+    binner = VelBinner(n_bin=nbin, fs=fs, n_fft=nfft)
     # Always 50% overlap if numbers reshape perfectly
     # Mean square sound pressure
     psd = binner.power_spectral_density(pressure, freq_units="Hz")
@@ -221,9 +231,9 @@ def sound_pressure_spectral_density(
             "units": pressure.units + "^2/Hz",
             "long_name": long_name,
             "fs": fs,
-            "nbin": str(bin_length) + " s",
+            "bin_length": bin_length,
             "overlap": "50%",
-            "nfft": nbin,
+            "n_fft": nfft,
         },
     )
 
@@ -234,6 +244,7 @@ def apply_calibration(
     spsd: xr.DataArray,
     sensitivity_curve: xr.DataArray,
     fill_value: Union[float, int, np.ndarray],
+    interp_method: str = "linear",
 ) -> xr.DataArray:
     """
     Applies custom calibration to spectral density values.
@@ -248,6 +259,9 @@ def apply_calibration(
     fill_value: float or int
         Value with which to fill missing values from the calibration curve,
         in units of dB rel 1 V^2/uPa^2.
+    interp_method: str
+        Interpolation method to use when interpolating the calibration curve
+        to the frequencies in 'spsd'. Default is 'linear'.
 
     Returns
     -------
@@ -259,8 +273,7 @@ def apply_calibration(
         raise TypeError("'spsd' must be an xarray.DataArray.")
     if not isinstance(sensitivity_curve, xr.DataArray):
         raise TypeError("'sensitivity_curve' must be an xarray.DataArray.")
-    if not isinstance(fill_value, (int, float, np.ndarray)):
-        raise TypeError("'fill_value' must be a numeric type (int or float).")
+    _check_numeric(fill_value, "fill_value")
 
     # Ensure 'freq' dimension exists in 'spsd'
     if "freq" not in spsd.dims:
@@ -295,7 +308,7 @@ def apply_calibration(
     freq = sensitivity_curve.dims[0]
     # Interpolate calibration curve to desired value
     calibration = sensitivity_curve.interp(
-        {freq: spsd_calibrated["freq"]}, method="linear"
+        {freq: spsd_calibrated["freq"]}, method=interp_method
     )
     # Fill missing with provided value
     calibration = calibration.fillna(fill_value)
@@ -340,6 +353,7 @@ def sound_pressure_spectral_density_level(spsd: xr.DataArray) -> xr.DataArray:
         attrs={
             "units": "dB re 1 uPa^2/Hz",
             "long_name": "Sound Pressure Spectral Density Level",
+            "time_resolution": spsd.attrs["bin_length"],
         },
     )
 
@@ -571,8 +585,8 @@ def band_aggregate(
     for val in octave:
         if not isinstance(val, int) or (val <= 0):
             raise TypeError("'octave' must contain positive integers.")
-    if not isinstance(fmin, int) or (fmin <= 0):
-        raise TypeError("'fmin' must be a positive integer.")
+    _check_numeric(fmin, "fmax")
+    _check_numeric(fmax, "fmax")
     if fmax <= fmin:  # also checks that fmax is positive
         raise ValueError("'fmax' must be greater than 'fmin'.")
 
diff --git a/mhkit/acoustics/graphics.py b/mhkit/acoustics/graphics.py
index fb61361f..17fb9e94 100644
--- a/mhkit/acoustics/graphics.py
+++ b/mhkit/acoustics/graphics.py
@@ -24,7 +24,7 @@
 import xarray as xr
 import matplotlib.pyplot as plt
 
-from .analysis import _fmax_warning
+from .analysis import _fmax_warning, _check_numeric
 
 
 def plot_spectrogram(
@@ -61,8 +61,9 @@ def plot_spectrogram(
         Figure plot axis
     """
 
-    if not isinstance(fmin, (int, float)) or not isinstance(fmax, (int, float)):
-        raise TypeError("fmin and fmax must be numeric types.")
+    # Type checks
+    _check_numeric(fmin, "fmin")
+    _check_numeric(fmax, "fmax")
     if fmin >= fmax:
         raise ValueError("fmin must be less than fmax.")
 
@@ -128,8 +129,8 @@ def plot_spectra(
         Figure plot axis
     """
 
-    if not isinstance(fmin, (int, float)) or not isinstance(fmax, (int, float)):
-        raise TypeError("fmin and fmax must be numeric types.")
+    _check_numeric(fmin, "fmin")
+    _check_numeric(fmax, "fmax")
     if fmin >= fmax:
         raise ValueError("fmin must be less than fmax.")
 
diff --git a/mhkit/acoustics/io.py b/mhkit/acoustics/io.py
index c1743b0e..cf836e4f 100644
--- a/mhkit/acoustics/io.py
+++ b/mhkit/acoustics/io.py
@@ -49,6 +49,8 @@
 import xarray as xr
 from scipy.io import wavfile
 
+from mhkit.acoustics.analysis import _check_numeric
+
 
 def _read_wav_metadata(f: BinaryIO) -> dict:
     """
@@ -132,10 +134,9 @@ def _calculate_voltage_and_time(
         raise TypeError("Raw audio data 'raw' must be a numpy.ndarray.")
     if not isinstance(bits_per_sample, int):
         raise TypeError("'bits_per_sample' must be an integer.")
-    if not isinstance(peak_voltage, (int, float)):
-        raise TypeError("'peak_voltage' must be numeric (int or float).")
     if not isinstance(start_time, (str, np.datetime64)):
         raise TypeError("'start_time' must be a string or np.datetime64.")
+    _check_numeric(peak_voltage, "peak_voltage")
 
     length = raw.shape[0] // fs  # length of recording in seconds
 
@@ -196,15 +197,12 @@ def read_hydrophone(
 
     if not isinstance(filename, (str, Path)):
         raise TypeError("Filename must be a string or a pathlib.Path object.")
-    if not isinstance(peak_voltage, (int, float)):
-        raise TypeError("'peak_voltage' must be numeric (int or float).")
-    if sensitivity is not None and not isinstance(sensitivity, (int, float)):
-        raise TypeError("'sensitivity' must be numeric (int, float) or None.")
-    if not isinstance(gain, (int, float)):
-        raise TypeError("'gain' must be numeric (int or float).")
+    if sensitivity is not None:
+        _check_numeric(sensitivity, "sensitivity")
+    _check_numeric(peak_voltage, "peak_voltage")
+    _check_numeric(gain, "gain")
     if not isinstance(start_time, (str, np.datetime64)):
         raise TypeError("'start_time' must be a string or np.datetime64")
-
     if (sensitivity is not None) and (sensitivity > 0):
         raise ValueError(
             "Hydrophone calibrated sensitivity should be entered as a negative number."
@@ -225,9 +223,9 @@ def read_hydrophone(
     # If sensitivity is provided, convert to sound pressure
     if sensitivity is not None:
         # Subtract gain
-        # Hydrophone with sensitivity of -177 dB and gain of -3 dB = sensitivity of -174 dB
+        # Hydrophone with sensitivity of -177 dB and gain of 3 dB = sensitivity of -174 dB
         if gain:
-            sensitivity -= gain
+            sensitivity += gain
         # Convert calibration from dB rel 1 V/uPa into ratio
         sensitivity = 10 ** (sensitivity / 20)  # V/uPa
 
@@ -511,25 +509,18 @@ def export_audio(
     -------
     None
     """
+
     if not isinstance(filename, str):
         raise TypeError("'filename' must be a string.")
-
     if not isinstance(pressure, xr.DataArray):
         raise TypeError("'pressure' must be an xarray.DataArray.")
-
     if not hasattr(pressure, "values") or not isinstance(pressure.values, np.ndarray):
         raise TypeError("'pressure.values' must be a numpy.ndarray.")
-
-    if not hasattr(pressure, "sensitivity") or not isinstance(
-        pressure.sensitivity, (int, float)
-    ):
-        raise TypeError("'pressure.sensitivity' must be a numeric type (int or float).")
-
-    if not hasattr(pressure, "fs") or not isinstance(pressure.fs, (int, float)):
-        raise TypeError("'pressure.fs' must be a numeric type (int or float).")
-
-    if not isinstance(gain, (int, float)):
-        raise TypeError("'gain' must be a numeric type (int or float).")
+    if not hasattr(pressure, "sensitivity"):
+        _check_numeric(pressure.sensitivity, "pressure.sensitivity")
+    if not hasattr(pressure, "fs"):
+        _check_numeric(pressure.fs, "pressure.fs")
+    _check_numeric(gain, "gain")
 
     # Convert from Pascals to UPa
     upa = pressure.values.T * 1e6
diff --git a/mhkit/acoustics/sel.py b/mhkit/acoustics/sel.py
index 781db387..9083dc16 100644
--- a/mhkit/acoustics/sel.py
+++ b/mhkit/acoustics/sel.py
@@ -134,9 +134,7 @@ def sound_exposure_level(
     exposure = np.trapezoid(band * w, band["freq"])
 
     # Sound exposure level (L_{E,p}) = (L_{p,rms} + 10log10(t))
-    sel = 10 * np.log10(exposure / reference) + 10 * np.log10(
-        spsd.attrs["nfft"] / spsd.attrs["fs"]  # n_points / (n_points/s)
-    )
+    sel = 10 * np.log10(exposure / reference) + 10 * np.log10(spsd.attrs["bin_length"])
 
     out = xr.DataArray(
         sel.astype(np.float32),
@@ -145,7 +143,7 @@ def sound_exposure_level(
             "units": "dB re 1 uPa^2 s",
             "long_name": long_name,
             "weighting_group": group,
-            "integration_time": spsd.attrs["nbin"],
+            "integration_time": spsd.attrs["bin_length"],
             "freq_band_min": fmin,
             "freq_band_max": fmax,
         },
diff --git a/mhkit/acoustics/spl.py b/mhkit/acoustics/spl.py
index 2e9ef86a..3be616c9 100644
--- a/mhkit/acoustics/spl.py
+++ b/mhkit/acoustics/spl.py
@@ -19,7 +19,7 @@
 import numpy as np
 import xarray as xr
 
-from .analysis import _fmax_warning, _create_frequency_bands
+from .analysis import _check_numeric, _fmax_warning, _create_frequency_bands
 
 
 def _argument_check(spsd, fmin, fmax):
@@ -45,10 +45,8 @@ def _argument_check(spsd, fmin, fmax):
     # Type checks
     if not isinstance(spsd, xr.DataArray):
         raise TypeError("'spsd' must be an xarray.DataArray.")
-    if not isinstance(fmin, int):
-        raise TypeError("'fmin' must be an integer.")
-    if not isinstance(fmax, int):
-        raise TypeError("'fmax' must be an integer.")
+    _check_numeric(fmin, "fmin")
+    _check_numeric(fmax, "fmax")
 
     # Ensure 'freq' and 'time' dimensions are present
     if ("freq" not in spsd.dims) or ("time" not in spsd.dims):
@@ -59,9 +57,9 @@ def _argument_check(spsd, fmin, fmax):
         raise ValueError(
             "'spsd' must have 'fs' (sampling frequency) in its attributes."
         )
-    if "nfft" not in spsd.attrs:
+    if "n_fft" not in spsd.attrs:
         raise ValueError(
-            "'spsd' must have 'nfft' (sampling frequency) in its attributes."
+            "'spsd' must have 'n_fft' (number of points in each FFT) in its attributes."
         )
 
     # Value checks
@@ -119,6 +117,7 @@ def sound_pressure_level(
         attrs={
             "units": "dB re 1 uPa",
             "long_name": "Sound Pressure Level",
+            "time_resolution": spsd.attrs["bin_length"],
             "freq_band_min": fmin,
             "freq_band_max": fmax,
         },
@@ -235,6 +234,7 @@ def third_octave_sound_pressure_level(
         {
             "units": "dB re 1 uPa",
             "long_name": "Third Octave Sound Pressure Level",
+            "time_resolution": spsd.attrs["bin_length"],
         }
     )
 
@@ -272,6 +272,7 @@ def decidecade_sound_pressure_level(
         {
             "units": "dB re 1 uPa",
             "long_name": "Decidecade Sound Pressure Level",
+            "time_resolution": spsd.attrs["bin_length"],
         }
     )
 
diff --git a/mhkit/tests/acoustics/test_analysis.py b/mhkit/tests/acoustics/test_analysis.py
index ce792fb3..b60f5f91 100644
--- a/mhkit/tests/acoustics/test_analysis.py
+++ b/mhkit/tests/acoustics/test_analysis.py
@@ -52,7 +52,8 @@ def test_sound_pressure_spectral_density(self):
         self.assertIn("freq", spsd.dims)
         self.assertIn("time", spsd.dims)
         self.assertEqual(spsd.attrs["units"], "Pa^2/Hz")
-        self.assertEqual(spsd.attrs["nbin"], f"{bin_length} s")
+        self.assertEqual(spsd.attrs["bin_length"], bin_length)
+        self.assertEqual(spsd.attrs["n_fft"], bin_length * fs)
 
         # Calculate expected number of segments
         overlap = 0.0