My very reason for getting involved with Python was to use it as a gui for some command line programs, like eac3to, sox and neroaacenc. Previously I'd been using batch in windows and had become quite proficient.

In batch, a line to process audio with sox looks like this:

"tools\sox.exe" "name.wav" "namesox.wav" compand 0.3,1 6:-60,-50,-30 -14 -90 0.2 gain -n -1

In Python, to make it work I have to insert ' and " all over the place.

soxxy='"'+'"'+"tools\sox.exe"+'"'+' '+'"'+name+'.wav'+'"'+" "+'"'+ name+'sox.wav'+'"'+' compand 0.3,1 6:-60,-50,-30 -14 -90 0.2'+'"'

Clearly I am approaching this from the wrong direction. Could someone please point me in the correct one?

This should work (note the single quote at the beginning and end-Python uses both/either) but print "soxxy" to be sure.
soxxy = '"tools\sox.exe" "%s.wav" "%ssox.wav" compand 0.3,1 6:-60,-50,-30 -14 -90 0.2
gain -n -1' % (name, name)

string formatting

path = 'c:\\aPath'
arg1 = 'an argument'
arg2 = 6
'%s "%s" %s' % (path, arg1, arg2) 
# returns
'c:\\aPath "an argument" 6

%s tells python you want to insert something into the string
It replaces every occurrence of %s with what you supply it with
in the following tuple. Make sure the number of %s matches the
number of items in the tuple. It's documented here:

Thanks guys. I have read about this but it never occured to me to use it here. The brain just needed a little push!
I'll go play...

Windows complains. It needs " at the start and end. I can do it with +'"', just did to prove it. Is there a better way?

just add the quotes where you need them in your string

'"This is a %s"' % 'test'
# returns
"This is a test"

You can add as many quotes as you like

If you need to add both single and double quotes surround your string in triple quotes, ie:

"""This 'is' a "%s" """ % 'test'
# returns
This 'is' a "test"

It is probably the blackslash which has a unique meaning in programming. Python uses a forward slash and converts depending on the OS. You can insert quotes just like any other string.

#  changed to a forward slash
soxxy = '%stools/sox.exe%s "%s.wav" "%ssox.wav" compand 0.3,1 6:-60,-50,-30 -14 -90 0.2 
 gain -n -1' % (quote, quote, name, name)
# etc.
print soxxy

# or use join
name = "xyz"
           '"%s.wav"' % (name),
           '"%ssox.wav"' % (name),
           'compand 0.3,1 6:-60,-50,-30 -14 -90 0.2  gain -n -1']

print " ".join(start_list)