diff --git a/QtPyLoT.py b/QtPyLoT.py
index 2251a763..3eeac515 100755
--- a/QtPyLoT.py
+++ b/QtPyLoT.py
@@ -54,6 +54,7 @@ from pylot.core.util.defaults import FILTERDEFAULTS, COMPNAME_MAP, \
 from pylot.core.util.errors import FormatError, DatastructureError, \
     OverwriteError
 from pylot.core.util.connection import checkurl
+from pylot.core.util.dataprocessing import read_metadata
 from pylot.core.util.utils import fnConstructor, getLogin, \
     full_range
 from pylot.core.io.location import create_creation_info, create_event
@@ -1004,6 +1005,7 @@ class MainWindow(QMainWindow):
                 if ans == QMessageBox.Yes:
                     settings.setValue("inventoryFile", fninv)
                     settings.sync()
+            metadata = read_metadata(fninv)
             for a in o.arrivals:
                 if a.phase in 'sS':
                     continue
@@ -1014,12 +1016,13 @@ class MainWindow(QMainWindow):
                     continue
                 onset = pick.time
                 dist = degrees2kilometers(a.distance)
-                w0, fc = calcsourcespec(wf, onset, fninv, self.inputs.get('vp'), dist,
+                w0, fc = calcsourcespec(wf, onset, metadata, self.inputs.get('vp'), dist,
                                         a.azimuth, a.takeoff_angle,
                                         self.inputs.get('Qp'), 0)
                 if w0 is None or fc is None:
                     continue
-                station_mag = calcMoMw(wf, w0, 2700., 3000., dist, fninv)
+                station_mag = calcMoMw(wf, w0, self.inputs.get('rho'),
+                                       self.inputs.get('vp'), dist)
                 mags[station] = station_mag
             mag = np.median([M[1] for M in mags.values()])
             # give some information on the processing
diff --git a/pylot/core/analysis/magnitude.py b/pylot/core/analysis/magnitude.py
index 488c0388..b65c9ab2 100644
--- a/pylot/core/analysis/magnitude.py
+++ b/pylot/core/analysis/magnitude.py
@@ -141,8 +141,8 @@ class Magnitude(object):
     def setinvdir(self, invdir):
         self.invdir = invdir
 
-    def getinvdir(self):
-        return self.invdir
+    def get_metadata(self):
+        return read_metadata(self.invdir)
 
     def getpicdic(self):
         return self.picdic
@@ -243,7 +243,7 @@ class M0Mw(Magnitude):
                 # call subfunction to estimate source spectrum
                 # and to derive w0 and fc
                 [w0, fc] = calcsourcespec(selwf, picks[key]['P']['mpp'], \
-                                          self.getinvdir(), self.getvp(), delta, az, \
+                                          self.get_metadata(), self.getvp(), delta, az, \
                                           inc, self.getQp(), self.getiplot())
 
                 if w0 is not None:
@@ -251,8 +251,8 @@ class M0Mw(Magnitude):
                     zdat = selwf.select(component="Z")
                     if len(zdat) == 0:  # check for other components
                         zdat = selwf.select(component="3")
-                    [Mo, Mw] = calcMoMw(zdat, w0, self.getrho(), self.getvp(), \
-                                        delta, self.getinvdir())
+                    [Mo, Mw] = calcMoMw(zdat, w0, self.getrho(), self.getvp(),
+                                        delta)
                 else:
                     Mo = None
                     Mw = None
@@ -265,7 +265,7 @@ class M0Mw(Magnitude):
                 self.picdic = picks
 
 
-def calcMoMw(wfstream, w0, rho, vp, delta, inv):
+def calcMoMw(wfstream, w0, rho, vp, delta):
     '''
     Subfunction of run_calcMoMw to calculate individual
     seismic moments and corresponding moment magnitudes.
@@ -306,7 +306,7 @@ def calcMoMw(wfstream, w0, rho, vp, delta, inv):
     return Mo, Mw
 
 
-def calcsourcespec(wfstream, onset, invdir, vp, delta, azimuth, incidence,
+def calcsourcespec(wfstream, onset, metadata, vp, delta, azimuth, incidence,
                    qp, iplot):
     '''
     Subfunction to calculate the source spectrum and to derive from that the plateau
@@ -321,8 +321,9 @@ def calcsourcespec(wfstream, onset, invdir, vp, delta, azimuth, incidence,
     :param: onset, P-phase onset time
     :type: float
 
-    :param: invdir, path to inventory or dataless-SEED file
-    :type:  string
+    :param: metadata, tuple or list containing type of inventory and either
+    list of files or inventory object
+    :type:  tuple or list
 
     :param: vp, Vp-wave velocity
     :type:  float
@@ -354,7 +355,7 @@ def calcsourcespec(wfstream, onset, invdir, vp, delta, azimuth, incidence,
     data = Data()
     wf_copy = wfstream.copy()
 
-    invtype, inventory = read_metadata(invdir)
+    invtype, inventory = metadata
 
     [cordat, restflag] = restitute_data(wf_copy, invtype, inventory)
     if restflag is True: