Merge pull request #3 from kowallus/master

Added tzxwav option to decode stereo tape only from a specified channel

docs/tzxwav.md

@@ -11,7 +11,7 @@ Reads ZX Spectum tapes from a WAV file and converts it to TZX.
 ```
 tzxwav [-h] [-o TARGET] [-p] [-v] [-t {low,med,high}]
        [-T {low,med,high}] [-l {none,short,normal,long}] [-c CLOCK]
-       [-s START] [-e END] [-D] file
+       [-s START] [-e END] [-S {left,mix,right}] [-D] file
 ```
 
 * `file`: WAV file to read from. Supported is mono and stereo, 8 and 16 bit per channel, any sampling rate. Other file formats are not supported.
@@ -24,6 +24,7 @@ tzxwav [-h] [-o TARGET] [-p] [-v] [-t {low,med,high}]
 * `-s`, `--start`: Set the first frame of the WAV file to be read. If not set, the start of file is used.
 * `-e`, `--end`: Set the last frame of the WAV file to be read. For technical reasons, this limit may be exceeded by a few frames. If not set, or if set out of range, the file will be read to the end.
 * `-c`, `--clock`: Change reference Z80 CPU clock speed, in Hz. Default is 3500000. It is also useful for correcting a wrong playback speed. For example, if your tape was played back 5% too fast, adjust the clock to 3500000 * 5% = 3675000 to improve the results.
+* `-S`, `--stereo`: Select channel of the stereo WAV file to be used. Default is `mix` of both channels.
 * `-D`, `--debug`: Show debugging output. Useful for finding out why `tzxwav` was unable to correctly read a file. Prints detected blocks and their position frame in the WAV file. If given two times, also prints detected bits and bytes. If given three times, prints detected pulse lengths (in T states) and their WAV file position. If give four times, also prints the reason why a sync or bit pulse was rejected. Attention, it will create a *lot* of useless output!
 * `-h`, `--help`: Show help message and exit.
 

tzxlib/loader.py

@@ -33,9 +33,9 @@ def sgn(val):
 def unpackMono(data, size):
     return unpack('<' + size, data)[0]
 
-def unpackStereo(data, size):
+def unpackStereo(data, size, leftMix = 0.5):
     val = unpack('<' + size + size, data)
-    return (val[0] + val[1]) / 2
+    return (val[0] * leftMix + val[1] * (1 - leftMix))
 
 class TapeLoader():
 
@@ -46,9 +46,9 @@ class TapeLoader():
     lowT    =  855      # 0 bit pulse
     highT   = 1710      # 1 bit pulse
 
-    def __init__(self, progress=None, debug=None, verbose=False, treshold=3500, tolerance=1.2, leaderMin=20, cpufreq=3500000):
+    def __init__(self, progress=None, debug=None, verbose=False, treshold=3500, tolerance=1.2, leaderMin=20, cpufreq=3500000, leftChMix=0.5):
         maxlenT = self.leaderT * 2.2 * tolerance
-        self.samples = TapeReader(progress=progress, cpufreq=cpufreq, maxlenT=maxlenT)
+        self.samples = TapeReader(progress=progress, cpufreq=cpufreq, maxlenT=maxlenT, leftChMix=leftChMix)
         self.debug = debug if debug is not None else 0
         self.verbose = verbose
         self.treshold = treshold
@@ -317,13 +317,14 @@ def _showBlock(self, tap, leaderPos, syncPos, endPos):
 
 
 class TapeReader():
-    def __init__(self, progress=None, cpufreq=3500000, maxlenT=6000):
+    def __init__(self, progress=None, cpufreq=3500000, maxlenT=6000, leftChMix=0.5):
         self.cpufreq = cpufreq
         self.progress = progress
         self.maxlenT = maxlenT
         self.invert = False
         self.startFrame = None
         self.endFrame = None
+        self.leftChMix = leftChMix
 
     def open(self, filename):
         """ Opens the given WAV file name """
@@ -423,11 +424,11 @@ def _createReader(self):
         channels = self.wav.getnchannels()
         bpc = self.wav.getsampwidth()
         if bpc == 2:
-            if channels == 2:   return lambda f: unpackStereo(f, 'h')
+            if channels == 2:   return lambda f: unpackStereo(f, 'h', self.leftChMix)
             elif channels == 1: return lambda f: unpackMono(f, 'h')
             else:               raise IOError('Cannot handle WAV files with {} channels'.format(channels))
         elif bpc == 1:
-            if channels == 2:   return lambda f: unpackStereo(f, 'b') * 256
+            if channels == 2:   return lambda f: unpackStereo(f, 'b', self.leftChMix) * 256
             elif channels == 1: return lambda f: unpackMono(f, 'b') * 256
             else:               raise IOError('Cannot handle WAV files with {} channels'.format(channels))
         else:

tzxwav

@@ -29,6 +29,7 @@ from tzxlib.loader import TapeLoader
 tresholds  = { 'low': 500, 'med': 2500, 'high':5000 }
 tolerances = { 'low': 1.1,  'med': 1.2,  'high': 1.4 }
 leaderMins = { 'none': 2, 'short': 10, 'normal': 40, 'long': 100 }
+leftChMix = { 'left': 1,  'mix': 0.5,  'right': 0 }
 
 lastPercent = None
 startTime = None
@@ -92,6 +93,11 @@ parser.add_argument('-e', '--end',
             dest='end',
             type=int,
             help='End at WAV frame number')
+parser.add_argument('-S', '--stereo',
+            choices=['left', 'mix', 'right'],
+            default='mix',
+            dest='leftChMix',
+            help='channel selection (works only for stereo WAV files)')
 parser.add_argument('-D', '--debug',
             dest='debug',
             action='count',
@@ -103,6 +109,7 @@ loader = TapeLoader(debug=args.debug,
         treshold=tresholds[args.treshold],
         tolerance=tolerances[args.tolerance],
         leaderMin=leaderMins[args.leader],
+        leftChMix=leftChMix[args.leftChMix],
         cpufreq=args.clock,
         progress=showProgress if args.progress else None,
         verbose=args.verbose)