diff --git a/.gitignore b/.gitignore
index c937b44..3021a61 100644
--- a/.gitignore
+++ b/.gitignore
@@ -18,4 +18,4 @@ test/test_workers
 doc
 LASP.egg-info
 lasp_octave_fir.*
-lasp/aps_ui.py
+lasp/ui_*
diff --git a/lasp/__init__.py b/lasp/__init__.py
index e96bd63..54bf4e6 100644
--- a/lasp/__init__.py
+++ b/lasp/__init__.py
@@ -1,3 +1,3 @@
 from .wrappers import *
-from .tools import *
-P_REF = 2e-5
+from .lasp_tools import *
+from .lasp_common import *
\ No newline at end of file
diff --git a/lasp/c/lasp_alg.h b/lasp/c/lasp_alg.h
index 1443576..b26daf0 100644
--- a/lasp/c/lasp_alg.h
+++ b/lasp/c/lasp_alg.h
@@ -25,10 +25,10 @@ static inline d vd_dot(const vd * a,const vd* b) {
     return d_dot(getvdval(a,0),getvdval(b,0),a->n_rows);
 }
 
-/** 
+/**
  * y = fac * y
  *
- * @param y 
+ * @param y
  * @param fac scale factor
  */
 static inline void dmat_scale(dmat* y,const c fac){
@@ -38,10 +38,10 @@ static inline void dmat_scale(dmat* y,const c fac){
     }
 
 }
-/** 
+/**
  * y = fac * y
  *
- * @param y 
+ * @param y
  * @param fac scale factor
  */
 static inline void cmat_scale(cmat* y,const c fac){
diff --git a/lasp/c/lasp_filterbank.c b/lasp/c/lasp_filterbank.c
index 34b2c73..8ca4512 100644
--- a/lasp/c/lasp_filterbank.c
+++ b/lasp/c/lasp_filterbank.c
@@ -98,11 +98,13 @@ dmat FilterBank_filter(FilterBank* fb,
 
     dmat input_block = dmat_alloc(nfft,1);
 
-    /* Output is ready to be multiplied with FFt'th filter */
+    /* FFT'th filter coefficients */
     cmat input_fft = cmat_alloc(nfft/2+1,1);
 
-    /* Output is ready to be multiplied with FFt'th filter */
+    /* Output of the fast convolution */
     cmat output_fft = cmat_alloc(nfft/2+1,nfilters);
+
+    /* Inverse FFT'th output */
     dmat output_block = dmat_alloc(nfft,nfilters);
 
     while (dFifo_size(input_fifo) >= nfft) {
@@ -111,6 +113,7 @@ dmat FilterBank_filter(FilterBank* fb,
                                 &input_block,
                                 fb->P_m_1 /* save P-1 samples */
             );
+        
         dbgassert(nsamples == nfft,"BUG in dFifo");
 
         Fft_fft(fb->fft,&input_block,&input_fft);
@@ -127,7 +130,9 @@ dmat FilterBank_filter(FilterBank* fb,
                         
             vc_free(&output_fft_col);
             vc_free(&filter_col);
+            
         }
+        
         vc_free(&input_fft_col);
 
         Fft_ifft(fb->fft,&output_fft,&output_block);
@@ -136,6 +141,8 @@ dmat FilterBank_filter(FilterBank* fb,
                                          fb->P_m_1,0, /* startrow, startcol */
                                          nfft-fb->P_m_1, /* Number of rows */
                                          output_block.n_cols);
+
+        /* Push the valid samples to the output FIFO */
         dFifo_push(fb->output_fifo,&valid_samples);
         dmat_free(&valid_samples);
 
diff --git a/lasp/c/lasp_mat.h b/lasp/c/lasp_mat.h
index f4e31c9..e1b8421 100644
--- a/lasp/c/lasp_mat.h
+++ b/lasp/c/lasp_mat.h
@@ -357,9 +357,11 @@ static inline void dmat_copy_rows(dmat* to,const dmat* from,
                                   us startrow_from,
                                   us nrows) {
     us col,ncols = to->n_cols;
-
+    dbgassert(to && from,NULLPTRDEREF);
+    dbgassert(to->n_cols == from->n_cols,SIZEINEQUAL);
     dbgassert(startrow_from+nrows <= from->n_rows,OUTOFBOUNDSMATR);
     dbgassert(startrow_to+nrows <= to->n_rows,OUTOFBOUNDSMATR);
+
     for(col=0;col<ncols;col++) {
         d* to_d = getdmatval(to,startrow_to,col);
         d* from_d = getdmatval(from,startrow_from,col);
diff --git a/lasp/c/lasp_python.h b/lasp/c/lasp_python.h
index 286a286..f99e823 100644
--- a/lasp/c/lasp_python.h
+++ b/lasp/c/lasp_python.h
@@ -16,7 +16,14 @@
 #define LASP_NUMPY_FLOAT_TYPE NPY_FLOAT32
 #endif
 
-
+/** 
+ * Create a numpy array from an existing dmat.
+ *
+ * @param mat 
+ * @param transfer_ownership 
+ *
+ * @return 
+ */
 static inline PyObject* dmat_to_ndarray(dmat* mat,bool transfer_ownership) {
     fsTRACE(15);
     dbgassert(mat,NULLPTRDEREF);
diff --git a/lasp/fir_design/__init__.py b/lasp/filter_design/__init__.py
similarity index 100%
rename from lasp/fir_design/__init__.py
rename to lasp/filter_design/__init__.py
diff --git a/lasp/fir_design/fir_design.py b/lasp/filter_design/fir_design.py
similarity index 100%
rename from lasp/fir_design/fir_design.py
rename to lasp/filter_design/fir_design.py
diff --git a/lasp/filter_design/freqweighting_fir.py b/lasp/filter_design/freqweighting_fir.py
new file mode 100644
index 0000000..c419467
--- /dev/null
+++ b/lasp/filter_design/freqweighting_fir.py
@@ -0,0 +1,147 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""!
+Author: J.A. de Jong - ASCEE
+
+Description: Filter design for frequency weightings A and C.
+"""
+from .fir_design import freqResponse, arbitrary_fir_design
+from ..lasp_common import FreqWeighting
+import numpy as np
+
+__all__ = ['A','C','A_fir_design','C_fir_design',
+           'show_Afir','show_Cfir']
+
+fr = 1000.
+fL = 10**1.5
+fH = 10**3.9
+fLsq = fL**2
+fHsq = fH**2
+frsq = fr**2
+fA = 10**2.45
+D = np.sqrt(.5)
+
+b = (1/(1-D))*(frsq+fLsq*fHsq/frsq-D*(fLsq+fHsq))
+c = fLsq*fHsq
+f2 = (3-np.sqrt(5.))/2*fA
+f3 = (3+np.sqrt(5.))/2*fA
+f1 = np.sqrt((-b-np.sqrt(b**2-4*c))/2)
+f4 = np.sqrt((-b+np.sqrt(b**2-4*c))/2)
+f4sq = f4**2
+
+def A_uncor(f):
+    """
+    Computes the uncorrected frequency response of the A-filter
+    """
+    fsq = f**2
+    num  = f4sq*fsq**2
+    denom1 = (fsq+f1**2)
+    denom2 = np.sqrt((fsq+f2**2)*(fsq+f3**2))*(fsq+f4sq)
+    
+    return (num/(denom1*denom2))
+
+def A(f):
+    """
+    Computes the linear A-weighting freqency response
+    """
+    Auncor = A_uncor(f)
+    A1000 = A_uncor(1000.)
+    return Auncor/A1000
+        
+def C_uncor(f):
+    """
+    Computes the uncorrected frequency response of the C-filter
+    """
+    fsq = f**2
+    num  = f4sq*fsq
+    denom1 = (fsq+f1**2)
+    denom2 = (fsq+f4**2)
+    return num/(denom1*denom2)
+
+def C(f):
+    """
+    Computes the linear A-weighting freqency response
+    """
+    Cuncor = C_uncor(f)
+    C1000 = C_uncor(1000.)
+    return Cuncor/C1000
+    
+
+def A_fir_design():
+    fs = 48000.
+    freq_design = np.linspace(0,17e3,3000)
+    freq_design[-1] = fs/2
+    amp_design  = A(freq_design)
+    amp_design[-1] = 0.
+
+    L = 2048 # Filter order
+    fir = arbitrary_fir_design(fs,L,freq_design,amp_design,
+                               window='rectangular')
+    return fir
+
+
+def C_fir_design():
+    fs = 48000.
+    freq_design = np.linspace(0,17e3,3000)
+    freq_design[-1] = fs/2
+    amp_design  = C(freq_design)
+    amp_design[-1] = 0.
+
+    L = 2048 # Filter order
+    fir = arbitrary_fir_design(fs,L,freq_design,amp_design,
+                               window='rectangular')
+    return fir
+
+
+def show_Afir():
+    from asceefigs.plot import Bode, close, Figure
+    close('all')
+
+    fs = 48000.
+    freq_design = np.linspace(0,17e3,3000)
+    freq_design[-1] = fs/2
+    amp_design  = A(freq_design)
+    amp_design[-1] = 0.
+    firs = []
+    
+#    firs.append(arbitrary_fir_design(fs,L,freq_design,amp_design,window='hamming'))
+#    firs.append(arbitrary_fir_design(fs,L,freq_design,amp_design,window='hann'))
+    firs.append(A_fir_design())
+    #from scipy.signal import iirdesign
+    #b,a = iirdesign()
+    freq_check = np.logspace(0,np.log10(fs/2),5000)
+    f=Figure()
+    
+    f.semilogx(freq_check,20*np.log10(A(freq_check)))
+    for fir in firs:
+        H = freqResponse(fs,freq_check, fir)
+        f.plot(freq_check,20*np.log10(np.abs(H)))
+        
+    f.fig.get_axes()[0].set_ylim(-75,3)
+
+
+def show_Cfir():
+    from asceefigs.plot import Bode, close, Figure
+    close('all')
+
+    fs = 48000.
+    freq_design = np.linspace(0,17e3,3000)
+    freq_design[-1] = fs/2
+    amp_design  = C(freq_design)
+    amp_design[-1] = 0.
+    firs = []
+    
+#    firs.append(arbitrary_fir_design(fs,L,freq_design,amp_design,window='hamming'))
+#    firs.append(arbitrary_fir_design(fs,L,freq_design,amp_design,window='hann'))
+    firs.append(C_fir_design())
+    #from scipy.signal import iirdesign
+    #b,a = iirdesign()
+    freq_check = np.logspace(0,np.log10(fs/2),5000)
+    f=Figure()
+    
+    f.semilogx(freq_check,20*np.log10(C(freq_check)))
+    for fir in firs:
+        H = freqResponse(fs,freq_check, fir)
+        f.plot(freq_check,20*np.log10(np.abs(H)))
+        
+    f.fig.get_axes()[0].set_ylim(-30,1)
diff --git a/lasp/fir_design/octave_filter_design_fir.py b/lasp/filter_design/octave_filter_design_fir.py
similarity index 100%
rename from lasp/fir_design/octave_filter_design_fir.py
rename to lasp/filter_design/octave_filter_design_fir.py
diff --git a/lasp/fir_design/octave_filter_limits.py b/lasp/filter_design/octave_filter_limits.py
similarity index 100%
rename from lasp/fir_design/octave_filter_limits.py
rename to lasp/filter_design/octave_filter_limits.py
diff --git a/lasp/lasp_common.py b/lasp/lasp_common.py
new file mode 100644
index 0000000..0730b04
--- /dev/null
+++ b/lasp/lasp_common.py
@@ -0,0 +1,86 @@
+# -*- coding: utf-8 -*-
+#!/usr/bin/env python3
+import numpy as np
+"""
+Common definitions used throughout the code.
+"""
+
+__all__ = ['P_REF','FreqWeighting','TimeWeighting','getTime']
+
+# Reference sound pressure level
+P_REF = 2e-5
+
+class TimeWeighting:
+    none = (None,'Raw (no time weighting)')
+    ufast = (30e-3,'30 ms')
+    fast = (0.125,'Fast')
+    slow = (1.0,'Slow')
+    types = (none, ufast, fast, slow)
+    default = 2
+
+    @staticmethod
+    def fillComboBox(cb):
+        """
+        Fill TimeWeightings to a combobox
+
+        Args:
+            cb: QComboBox to fill
+        """
+        cb.clear()
+        for tw in TimeWeighting.types:
+            cb.addItem(tw[1],tw)
+        cb.setCurrentIndex(TimeWeighting.default)
+
+    def getCurrent(cb):
+        return TimeWeighting.types[cb.currentIndex()]
+
+class FreqWeighting:
+    """
+    Frequency weighting types
+    """
+    A=('A','A-weighting')
+    C=('C','C-weighting')
+    Z=('Z','Z-weighting')
+    types = (A,C,Z)
+    default = 0
+
+    @staticmethod
+    def fillComboBox(cb):
+        """
+        Fill FreqWeightings to a combobox
+
+        Args:
+            cb: QComboBox to fill
+        """
+        cb.clear()
+        for fw in FreqWeighting.types:
+            cb.addItem(fw[1],fw)
+        cb.setCurrentIndex(FreqWeighting.default)
+
+    def getCurrent(cb):
+        return FreqWeighting.types[cb.currentIndex()]
+
+def getTime(fs,N,start=0):
+    """
+    Return a time array for given number of points and sampling frequency.
+
+    Args:
+        fs: Sampling frequency [Hz]
+        N: Number of time samples
+        start: Optional start ofset in number of samples
+    """
+
+    return np.linspace(start/fs,N/fs,N,endpoint=False)
+
+
+def getFreq(fs, nfft):
+    """
+    return an array of frequencies for single-sided spectra
+
+    Args:
+        fs: Sampling frequency [Hz]
+        nfft: Fft length (int)
+    """
+    df = fs/nfft  # frequency resolution
+    K = nfft//2+1 # number of frequency bins
+    return np.linspace(0, (K-1)*df, K)
diff --git a/lasp/lasp_config.py b/lasp/lasp_config.py
new file mode 100644
index 0000000..1f0edeb
--- /dev/null
+++ b/lasp/lasp_config.py
@@ -0,0 +1,17 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""!
+Author: J.A. de Jong - ASCEE
+
+Description: LASP configuration
+"""
+import numpy as np
+
+LASP_NUMPY_FLOAT_TYPE = np.float64
+
+def zeros(shape):
+    return np.zeros(shape,dtype=LASP_NUMPY_FLOAT_TYPE)
+def ones(shape):
+    return np.ones(shape,dtype=LASP_NUMPY_FLOAT_TYPE)
+def empty(shape):
+    return np.empty(shape,dtype=LASP_NUMPY_FLOAT_TYPE)
\ No newline at end of file
diff --git a/lasp/lasp_measurement.py b/lasp/lasp_measurement.py
new file mode 100644
index 0000000..6ddd40f
--- /dev/null
+++ b/lasp/lasp_measurement.py
@@ -0,0 +1,171 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""!
+Author: J.A. de Jong - ASCEE
+
+Description: Measurement class
+"""
+import h5py as h5
+import numpy as np
+from .lasp_config import LASP_NUMPY_FLOAT_TYPE
+import wave,os
+
+class BlockIter:
+    def __init__(self,nblocks,faudio):
+        self.i = 0
+        self.nblocks = nblocks
+        self.fa = faudio
+    def __iter__(self):
+        return self
+    def __next__(self):
+        if self.i == self.nblocks:
+            raise StopIteration
+        self.i+=1
+        return self.fa[self.i-1][:,:]
+
+
+def getSampWidth(dtype):
+    if dtype == np.int32:
+        return 4
+    elif dtype == np.int16:
+        return 2
+    else:
+        raise ValueError('Invalid data type: %s' %dtype)
+
+
+def exportAsWave(fn,fs,data,force=False):
+    if not '.wav' in fn[-4:]:
+        fn += '.wav'
+
+    nchannels = data.shape[1]
+    sampwidth = getSampWidth(data.dtype)
+
+    if os.path.exists(fn) and not force:
+        raise RuntimeError('File already exists: %s', fn)
+
+    with wave.open(fn,'w') as wf:
+        wf.setparams((nchannels,sampwidth,fs,0,'NONE','NONE'))
+        wf.writeframes(np.asfortranarray(data).tobytes())
+
+
+class Measurement:
+    def __init__(self, fn):
+
+        if not '.h5' in fn:
+            fn += '.h5'
+
+        self.fn = fn
+
+        f = h5.File(fn,'r+')
+        self.f = f
+        try:
+            f['video']
+            self.has_video = True
+        except KeyError:
+            self.has_video = False
+
+        self.nblocks, self.blocksize, self.nchannels = f['audio'].shape
+        dtype = f['audio'].dtype
+        self.sampwidth = getSampWidth(dtype)
+
+        self.samplerate = f.attrs['samplerate']
+        self.N = (self.nblocks*self.blocksize)
+        self.T = self.N/self.samplerate
+
+        # comment = read-write thing
+        try:
+            self.f.attrs['comment']
+        except KeyError:
+            self.f.attrs['comment'] = ''
+
+    @property
+    def comment(self):
+        return self.f.attrs['comment']
+
+    @comment.setter
+    def comment(self, cmt):
+        self.f.attrs['comment'] = cmt
+
+    @property
+    def recTime(self):
+        return (self.blocksize*self.nblocks)/self.samplerate
+
+    @property
+    def time(self):
+        return self.f.attrs['time']
+
+    @property
+    def prms(self):
+        try:
+            return self._prms
+        except AttributeError:
+            pass
+        sens = self.sensitivity
+        pms = 0.
+        for block in self.iterBlocks():
+            pms += np.sum(block/sens)**2/self.N
+        self._prms = np.sqrt(pms)
+        return self._prms
+
+
+    def praw(self,block=None):
+        if block is not None:
+            blocks = self.f['audio'][block]
+        else:
+            blocks = []
+            for block in self.iterBlocks():
+                blocks.append(block)
+            blocks = np.asarray(blocks)
+
+            blocks = blocks.reshape(self.nblocks*self.blocksize,
+                                  self.nchannels)
+        if blocks.dtype == np.int32:
+            fac = 2**31
+        elif blocks.dtype == np.int16:
+            fac = 2**15
+        else:
+            raise RuntimeError('Unimplemented data type from recording: %s' %str(blocks.dtype))
+
+        blocks = blocks.astype(LASP_NUMPY_FLOAT_TYPE)/fac/self.sensitivity
+
+        return blocks
+
+    def iterBlocks(self):
+        return BlockIter(self.nblocks,self.f['audio'])
+
+    @property
+    def sensitivity(self):
+        try:
+            return self.f.attrs['sensitivity']
+        except:
+            return 1.0
+
+    @sensitivity.setter
+    def sensitivity(self, sens):
+        self.f.attrs['sensitivity'] = sens
+
+    def exportAsWave(self, fn=None, force=False):
+        """
+        Export measurement file as wave
+        """
+        if fn is None:
+            fn = self.fn
+            fn = os.path.splitext(fn)[0]
+
+        if not '.wav' in fn[-4:]:
+            fn += '.wav'
+
+        if os.path.exists(fn) and not force:
+            raise RuntimeError('File already exists: %s', fn)
+
+        with wave.open(fn,'w') as wf:
+            wf.setparams((self.nchannels,self.sampwidth,self.samplerate,0,'NONE','NONE'))
+            for block in self.iterBlocks():
+                wf.writeframes(np.asfortranarray(block).tobytes())
+
+
+    def __del__(self):
+        try:
+            self.f.close()
+        except AttributeError:
+            pass
diff --git a/lasp/lasp_slm.py b/lasp/lasp_slm.py
new file mode 100644
index 0000000..7e84e11
--- /dev/null
+++ b/lasp/lasp_slm.py
@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+Sound level meter implementation
+@author: J.A. de Jong - ASCEE
+"""
+from .wrappers import FilterBank, SPLowpass
+import numpy as np
+from .lasp_config import zeros
+from .lasp_common import TimeWeighting, P_REF
+__all__ = ['SLM']
+
+class Dummy:
+    def filter_(self, data):
+        return data
+
+class SLM:
+    """
+    Sound Level Meter, implements the single pole lowpass filter
+    """
+    def __init__(self, fs, weighcal,
+                 tw=TimeWeighting.default,
+                 nchannels = 1,
+                 freq=None, cal=None):
+
+        self._weighcal = weighcal
+        if tw is not TimeWeighting.none:
+            self._lps = [SPLowpass(fs, tw[0]) for i in range(nchannels)]
+        else:
+            self._lpw = [Dummy() for i in range(nchannels)]
+        self._Lmax = zeros(nchannels)
+
+    @property
+    def Lmax(self):
+        return self._Lmax
+
+    def addData(self, data):
+        assert data.ndim == 2
+        data_weighted = self._weighcal.filter_(data)
+
+        # Squared
+        sq = data_weighted**2
+        if sq.shape[0] == 0:
+            return np.array([])
+
+        tw = []
+        # Time-weight the signal
+        for chan,lp in enumerate(self._lps):
+            tw.append(lp.filter_(sq[:,chan])[:,0])
+        tw = np.asarray(tw).transpose()
+
+        Level = 10*np.log10(tw/P_REF**2)
+
+        curmax = np.max(Level)
+        if curmax > self._Lmax:
+            self._Lmax = curmax
+
+        return Level
diff --git a/lasp/lasp_tools.py b/lasp/lasp_tools.py
new file mode 100644
index 0000000..0113368
--- /dev/null
+++ b/lasp/lasp_tools.py
@@ -0,0 +1,8 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""!
+Author: J.A. de Jong - ASCEE
+
+Description:
+"""
+import numpy as np
diff --git a/lasp/lasp_weighcal.py b/lasp/lasp_weighcal.py
new file mode 100644
index 0000000..b174dda
--- /dev/null
+++ b/lasp/lasp_weighcal.py
@@ -0,0 +1,136 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+Weighting and calibration filter in one
+@author: J.A. de Jong - ASCEE
+"""
+from .filter_design.freqweighting_fir import A,C
+from .lasp_common import FreqWeighting
+from .filter_design.fir_design import (arbitrary_fir_design,
+                                       freqResponse as frp)
+from lasp.lasp_config import ones, empty
+from .wrappers import FilterBank
+import numpy as np
+
+__all__ = ['WeighCal']
+
+
+class WeighCal:
+    """
+    Time weighting and calibration FIR filter
+    """
+    def __init__(self, fw = FreqWeighting.default,
+                 nchannels = 1,
+                 fs = 48000.,
+                 calfile = None,
+                 sens=1.0):
+        """
+        Initialize the frequency weighting and calibration FIR filters.
+
+        Args:
+            fw: Frequency weighting to apply
+            nchannels: Number of channels for the input data
+            fs: Sampling frequency [Hz]
+            calfile: Calibration file to load.
+            sens: Sensitivity in units [\f$ Pa^{-1} \f$]
+        """
+
+        self.nchannels = nchannels
+        self.fs = fs
+        self.fw = fw
+        self.sens = sens
+        self.calfile = calfile
+
+        # Frequencies used for the filter design
+        freq_design = np.linspace(0,17e3,3000)
+        freq_design[-1] = fs/2
+
+        # Objective function for the frequency response
+        frp_obj = self.frpObj(freq_design)
+
+        self._firs = []
+        self._fbs = []
+        for chan in range(self.nchannels):
+            fir  = arbitrary_fir_design(fs,2048,freq_design,
+                                                  frp_obj[:,chan],
+                                                  window='rectangular')
+            self._firs.append(fir)
+
+            self._fbs.append(FilterBank(fir[:,np.newaxis],4096))
+
+        self._freq_design = freq_design
+
+    def filter_(self,data):
+        """
+        Filter data using the calibration and frequency weighting filter.
+        """
+        nchan = self.nchannels
+        assert data.shape[1] == nchan
+        assert data.shape[0] > 0
+
+        filtered = []
+        for chan in range(nchan):
+            filtered.append(self._fbs[chan].filter_(data[:,chan])[:,0])
+        filtered = np.asarray(filtered).transpose()/self.sens
+        if filtered.ndim == 1:
+            filtered = filtered[:,np.newaxis]
+        return filtered
+
+
+    def frpCalObj(self, freq_design):
+        """
+        Computes the objective frequency response of the calibration filter
+        """
+        calfile = self.calfile
+        if calfile is not None:
+            cal = np.loadtxt(calfile,skiprows=2)
+            freq = cal[:,0]
+            cal = cal[:,1:]
+            if cal.shape[1] != self.nchannels:
+                raise ValueError('Number of channels in calibration file does'
+                                 ' not equal to given number of channels')
+            calfac = 10**(-cal/20)
+            filter_calfac = empty((freq_design.shape[0],self.nchannels))
+
+            for chan in range(self.nchannels):
+                filter_calfac[:,chan] = np.interp(freq_design,freq,calfac[:,chan])
+
+        else:
+            filter_calfac = ones((freq_design.shape[0],self.nchannels,))
+
+        return filter_calfac
+
+    def frpWeightingObj(self, freq_design):
+        """
+        Computes the objective frequency response of the frequency weighting
+        filter.
+        """
+        fw = self.fw
+        if fw == FreqWeighting.A:
+            return A(freq_design)
+        elif fw == FreqWeighting.C:
+            return C(freq_design)
+        elif fw == FreqWeighting.Z:
+            return ones(freq_design.shape[0])
+        else:
+            raise ValueError('Invalid fw parameter')
+
+    def frpObj(self, freq_design):
+        """
+        Combines the frequency weighting and the calibration filter into
+        one frequency response objective function.
+        """
+        # Objective function for the frequency response
+        frp_objective = self.frpCalObj(freq_design) * \
+                        self.frpWeightingObj(freq_design)[:,np.newaxis]
+        frp_objective[-1] = 0.
+
+        return frp_objective
+
+    def freqResponse(self, chan=0, freq=None):
+        """
+        Returns the frequency response of the designed FIR filter
+        """
+        if freq is None:
+            freq = np.logspace(1,np.log10(self.fs/2),500)
+        return freq,frp(self.fs,freq,self._firs[chan]),self.frpObj(freq)[:,chan]
diff --git a/lasp/tools.py b/lasp/tools.py
deleted file mode 100644
index fbe8729..0000000
--- a/lasp/tools.py
+++ /dev/null
@@ -1,13 +0,0 @@
-#!/usr/bin/env python3
-# -*- coding: utf-8 -*-
-"""!
-Author: J.A. de Jong - ASCEE
-
-Description:
-"""
-import numpy as np
-
-def getFreq(fs, nfft):
-    df = fs/nfft  # frequency resolution 
-    K = nfft//2+1 # number of frequency bins
-    return np.linspace(0, (K-1)*df, K)
diff --git a/lasp/wrappers.pyx b/lasp/wrappers.pyx
index f59c68f..1ba6aca 100644
--- a/lasp/wrappers.pyx
+++ b/lasp/wrappers.pyx
@@ -98,8 +98,6 @@ cdef class Fft:
 
         return timedata
 
-
-
 cdef extern from "lasp_window.h":
     ctypedef enum WindowType:
         Hann
@@ -214,7 +212,7 @@ cdef class AvPowerSpectra:
         cdef vd weighting_vd
         cdef vd* weighting_ptr = NULL
         if(weighting.size != 0):
-            weighting_vd = dmat_foreign_data(weighting.n_rows,1,
+            weighting_vd = dmat_foreign_data(weighting.size,1,
                                              &weighting[0],False)
             weighting_ptr = &weighting_vd
         
@@ -295,7 +293,7 @@ cdef class FilterBank:
         cdef dmat hmat = dmat_foreign_data(h.shape[0],
                                            h.shape[1],
                                            &h[0,0],
-                                           True)
+                                           False)
 
         self.fb = FilterBank_create(&hmat,nfft)
         dmat_free(&hmat)
@@ -376,6 +374,9 @@ cdef class SPLowpass:
             SPLowpass_free(self.lp)
 
     def filter_(self,d[:] input_):
+        if input_.shape[0] == 0:
+            return np.array([],dtype=NUMPY_FLOAT_TYPE)
+        
         cdef vd input_vd = dmat_foreign_data(input_.shape[0],1,
                                              &input_[0],False)