Report volume like alsamixer. Maybe.

I have no idea how they calculate dB.

alsaaudio.c

@@ -77,6 +77,12 @@ typedef struct {
     snd_mixer_t *handle;
 } alsamixer_t;
 
+typedef enum {
+    unit_percent,
+    unit_dB,
+    unit_last
+} volume_unit_t;   
+
 /******************************************/
 /* PCM object wrapper                   */
 /******************************************/
@@ -1567,21 +1573,31 @@ Possible values in this list are:\n\
  - 'Capture Exclusive'\n");
 
 
-static int alsamixer_getpercentage(long min, long max, long value)
+static double alsamixer_getpercentage(long min, long max, long value)
 {
     /* Convert from number in range to percentage */
     int range = max - min;
-    int tmp;
 
     if (range == 0)
         return 0;
 
     value -= min;
-    tmp = rint((double)value/(double)range * 100);
-    return tmp;
+    return (double)value/(double)range * 100.0;
 }
 
-static long alsamixer_getphysvolume(long min, long max, int percentage)
+static double alsamixer_getdB(long min, long max, long value)
+{
+    /* Convert from number in range to dB */
+    int range = max - min;
+
+    if (range == 0)
+        return 0;
+
+    value -= min;
+    return log10((double)value/range) * 60.0;
+}
+
+static long alsamixer_getphysvolume(long min, long max, double percentage)
 {
     /* Convert from percentage to number in range */
     int range = max - min;
@@ -1590,57 +1606,76 @@ static long alsamixer_getphysvolume(long min, long max, int percentage)
     if (range == 0)
         return 0;
 
-    tmp = rint((double)range * ((double)percentage*.01)) + min;
+    tmp = rint((double)range * (percentage * .01)) + min;
     return tmp;
 }
 
 static PyObject *
-alsamixer_getvolume(alsamixer_t *self, PyObject *args)
+alsamixer_getvolume(alsamixer_t *self, PyObject *args, PyObject *kw)
 {
     snd_mixer_elem_t *elem;
     int channel;
     long ival;
-    PyObject *pcmtypeobj = NULL;
-    long pcmtype;
+    PyObject *dirobj = NULL;
+    long dir;
+    int unit = unit_percent;
     PyObject *result;
     PyObject *item;
 
-    if (!PyArg_ParseTuple(args,"|O:getvolume", &pcmtypeobj))
+    static char *kwlist[] = { "direction", "unit", NULL };
+    
+    if (!PyArg_ParseTupleAndKeywords(args, kw, "|Oi:getvolume", kwlist, &dirobj, &unit))
         return NULL;
 
+    if (unit >= unit_last) {
+        PyErr_SetString(PyExc_ValueError, "unit must be 'percent' or 'dB'");
+        return NULL;
+    }
+    
+    dir = get_pcmtype(dirobj);
+    if (dir < 0) {
+        return NULL;
+    }
+
     if (!self->handle)
     {
         PyErr_SetString(ALSAAudioError, "Mixer is closed");
         return NULL;
     }
 
-    pcmtype = get_pcmtype(pcmtypeobj);
-    if (pcmtype < 0) {
-        return NULL;
-    }
-
     elem = alsamixer_find_elem(self->handle,self->controlname,self->controlid);
 
     result = PyList_New(0);
 
     for (channel = 0; channel <= SND_MIXER_SCHN_LAST; channel++) {
-        if (pcmtype == SND_PCM_STREAM_PLAYBACK &&
+        if (dir == SND_PCM_STREAM_PLAYBACK &&
             snd_mixer_selem_has_playback_channel(elem, channel))
         {
             snd_mixer_selem_get_playback_volume(elem, channel, &ival);
-            item = PyLong_FromLong(alsamixer_getpercentage(self->pmin,
-                                                           self->pmax,
-                                                           ival));
+            if (unit == unit_percent) {
+                item = PyFloat_FromDouble(
+                    alsamixer_getpercentage(self->pmin, self->pmax, ival));
+            }
+            else {
+                item = PyFloat_FromDouble(
+                    alsamixer_getdB(self->pmin, self->pmax, ival));
+            }
             PyList_Append(result, item);
             Py_DECREF(item);
         }
-        else if (pcmtype == SND_PCM_STREAM_CAPTURE
+        else if (dir == SND_PCM_STREAM_CAPTURE
                  && snd_mixer_selem_has_capture_channel(elem, channel)
-                 && snd_mixer_selem_has_capture_volume(elem)) {
+                 && snd_mixer_selem_has_capture_volume(elem))
+        {
             snd_mixer_selem_get_capture_volume(elem, channel, &ival);
-            item = PyLong_FromLong(alsamixer_getpercentage(self->cmin,
-                                                           self->cmax,
-                                                           ival));
+            if (unit == unit_percent) {
+                item = PyFloat_FromDouble(
+                    alsamixer_getpercentage(self->cmin, self->cmax, ival));
+            }
+            else {
+                item = PyFloat_FromDouble(
+                    alsamixer_getdB(self->cmin, self->cmax, ival));
+            }
             PyList_Append(result, item);
             Py_DECREF(item);
         }
@@ -1650,15 +1685,17 @@ alsamixer_getvolume(alsamixer_t *self, PyObject *args)
 }
 
 PyDoc_STRVAR(getvolume_doc,
-"getvolume([pcmtype]) -> List of volume settings (int)\n\
+"getvolume(direction=PCM_PLAYBACK, unit=Percent) -> List of volume settings (float)\n\
 \n\
 Returns a list with the current volume settings for each channel.\n\
-The list elements are integer percentages.\n\
+The list elements are float percentages.\n\
 \n\
-The optional 'pcmtype' argument can be either PCM_PLAYBACK or\n\
+The 'direction' argument can be either PCM_PLAYBACK or\n\
 PCM_CAPTURE, which is relevant if the mixer can control both\n\
 playback and capture volume. The default value is PCM_PLAYBACK\n\
-if the mixer has this capability, otherwise PCM_CAPTURE");
+if the mixer has this capability, otherwise PCM_CAPTURE\
+\n\
+The optional 'unit' argument can be either 'percent' or 'dB'.");
 
 
 static PyObject *
@@ -1984,29 +2021,53 @@ This method will fail if the mixer has no capture switch capabilities.");
 
 
 static PyObject *
-alsamixer_setvolume(alsamixer_t *self, PyObject *args)
+alsamixer_setvolume(alsamixer_t *self, PyObject *args, PyObject *kw)
 {
     snd_mixer_elem_t *elem;
     int i;
-    long volume;
+    double volume = 0.0;
+    PyObject *volumeobj = NULL;
     int physvolume;
-    PyObject *pcmtypeobj = NULL;
-    long pcmtype;
+    PyObject *dirobj = NULL;
+    long dir;
+    int unit = unit_percent; 
     int channel = MIXER_CHANNEL_ALL;
     int done = 0;
 
-    if (!PyArg_ParseTuple(args,"l|iO:setvolume", &volume, &channel,
-                          &pcmtypeobj))
-        return NULL;
+    static char *kwlist[] = { "channel", "direction", "unit", NULL };
     
-    if (volume < 0 || volume > 100)
-    {
-        PyErr_SetString(ALSAAudioError, "Volume must be between 0 and 100");
+    
+    if (!PyArg_ParseTupleAndKeywords(args, kw, "O|iOi:setvolume", kwlist, &volumeobj, &channel,
+                                     &dirobj, &unit)) {
         return NULL;
     }
 
-    pcmtype = get_pcmtype(pcmtypeobj);
-    if (pcmtype < 0) {
+    // unit 
+    if (unit >= unit_last) {
+        PyErr_SetString(PyExc_ValueError, "unit must be 'percent' or 'dB'");
+        return NULL;
+    }
+
+    if (PyLong_Check(volumeobj)) {
+        volume = (double)PyLong_AsLong(volumeobj);
+    }
+    else if (PyFloat_Check(volumeobj)) {
+        volume = PyFloat_AsDouble(volumeobj);
+    }
+    else {
+        PyErr_SetString(PyExc_ValueError, "Volume must be integer or float");
+        return NULL;
+    }
+    
+    if (unit == unit_percent && (volume < 0.0 || volume > 100.0))
+    {
+        PyErr_SetString(PyExc_ValueError, "Volume in percent must be between 0 and 100");
+        return NULL;
+    }
+
+    // pcmtype
+    dir = get_pcmtype(dirobj);
+    if (dir < 0) {
         return NULL;
     }
 
@@ -2018,32 +2079,42 @@ alsamixer_setvolume(alsamixer_t *self, PyObject *args)
     
     elem = alsamixer_find_elem(self->handle,self->controlname,self->controlid);
 
-    if (!pcmtypeobj || (pcmtypeobj == Py_None))
+    if (!dirobj || (dirobj == Py_None))
     {
         if (self->pchannels)
-            pcmtype = SND_PCM_STREAM_PLAYBACK;
+            dir = SND_PCM_STREAM_PLAYBACK;
         else
-            pcmtype = SND_PCM_STREAM_CAPTURE;
+            dir = SND_PCM_STREAM_CAPTURE;
     }
 
     for (i = 0; i <= SND_MIXER_SCHN_LAST; i++)
     {
         if (channel == -1 || channel == i)
         {
-            if (pcmtype == SND_PCM_STREAM_PLAYBACK &&
+            if (dir == SND_PCM_STREAM_PLAYBACK &&
                 snd_mixer_selem_has_playback_channel(elem, i)) {
+                if (unit == unit_percent) {
                     physvolume = alsamixer_getphysvolume(self->pmin,
                                                          self->pmax, volume);
                     snd_mixer_selem_set_playback_volume(elem, i, physvolume);
+                }
+                else {
+                    snd_mixer_selem_set_playback_dB(elem, i, (long)(volume * 100.0), 0);
+                }
                 done++;
             }
-            else if (pcmtype == SND_PCM_STREAM_CAPTURE
+            else if (dir == SND_PCM_STREAM_CAPTURE
                      && snd_mixer_selem_has_capture_channel(elem, i)
                      && snd_mixer_selem_has_capture_volume(elem))
             {
+                if (unit == unit_percent) {
                     physvolume = alsamixer_getphysvolume(self->cmin, self->cmax,
                                                          volume);
                     snd_mixer_selem_set_capture_volume(elem, i, physvolume);
+                }
+                else {
+                    snd_mixer_selem_set_capture_dB(elem, i, (long)(volume * 100), 0);
+                }
                 done++;
             }
         }
@@ -2061,19 +2132,21 @@ alsamixer_setvolume(alsamixer_t *self, PyObject *args)
 }
 
 PyDoc_STRVAR(setvolume_doc,
-"setvolume(volume[[, channel] [, pcmtype]])\n\
+"setvolume(volume, channel=MIXER_CHANNEL_ALL, direction=PCM_PLAYBACK, unit='percent')\n\
 \n\
 Change the current volume settings for this mixer. The volume argument\n\
-controls the new volume setting as an integer percentage.\n\
+controls the new volume setting as a percentage.\n\
 If the optional argument channel is present, the volume is set only for\n\
 this channel. This assumes that the mixer can control the volume for the\n\
 channels independently.\n\
 \n\
-The optional direction argument can be either PCM_PLAYBACK or PCM_CAPTURE.\n\
+The optional 'direction' argument can be either PCM_PLAYBACK or PCM_CAPTURE.\n\
 It is relevant if the mixer has independent playback and capture volume\n\
 capabilities, and controls which of the volumes will be changed.\n\
-The default is 'playback' if the mixer has this capability, otherwise\n\
-'capture'.");
+The default is PCM_PLAYBACK if the mixer has this capability, otherwise\n\
+PCM_CAPTURE.\n\
+\n\
+The optional 'unit' argument can be either 'percent' (the default) or 'dB'.");
 
 
 static PyObject *
@@ -2084,6 +2157,7 @@ alsamixer_setmute(alsamixer_t *self, PyObject *args)
     int mute = 0;
     int done = 0;
     int channel = MIXER_CHANNEL_ALL;
+    
     if (!PyArg_ParseTuple(args,"i|i:setmute", &mute, &channel))
         return NULL;
 
@@ -2291,13 +2365,13 @@ static PyMethodDef alsamixer_methods[] = {
      switchcap_doc},
     {"volumecap", (PyCFunction)alsamixer_volumecap, METH_VARARGS,
      volumecap_doc},
-    {"getvolume", (PyCFunction)alsamixer_getvolume, METH_VARARGS,
+    {"getvolume", (PyCFunction)alsamixer_getvolume, METH_VARARGS | METH_KEYWORDS,
      getvolume_doc},
     {"getrange", (PyCFunction)alsamixer_getrange, METH_VARARGS, getrange_doc},
     {"getenum", (PyCFunction)alsamixer_getenum, METH_VARARGS, getenum_doc},
     {"getmute", (PyCFunction)alsamixer_getmute, METH_VARARGS, getmute_doc},
     {"getrec", (PyCFunction)alsamixer_getrec, METH_VARARGS, getrec_doc},
-    {"setvolume", (PyCFunction)alsamixer_setvolume, METH_VARARGS,
+    {"setvolume", (PyCFunction)alsamixer_setvolume, METH_VARARGS | METH_KEYWORDS,
      setvolume_doc},
     {"setenum", (PyCFunction)alsamixer_setenum, METH_VARARGS, setenum_doc},
     {"setmute", (PyCFunction)alsamixer_setmute, METH_VARARGS, setmute_doc},
@@ -2447,6 +2521,9 @@ PyObject *PyInit_alsaaudio(void)
     Py_INCREF(ALSAAudioError);
     PyModule_AddObject(m, "ALSAAudioError", ALSAAudioError);
 
+    _EXPORT_INT(m, "Percent", unit_percent);
+    _EXPORT_INT(m, "dB", unit_dB);
+
     _EXPORT_INT(m, "PCM_PLAYBACK",SND_PCM_STREAM_PLAYBACK);
     _EXPORT_INT(m, "PCM_CAPTURE",SND_PCM_STREAM_CAPTURE);
 

doc/libalsaaudio.rst

@@ -443,31 +443,35 @@ Mixer objects have the following methods:
    This method will fail if the mixer has no capture switch capabilities.
 
 
-.. method:: Mixer.getvolume([direction])
+.. method:: Mixer.getvolume(direction=PCM_PLAYBACK, unit=Percent)
 
    Returns a list with the current volume settings for each channel. The list
-   elements are integer percentages.
+   elements are percentages or dB values, depending on *unit*.
 
-   The optional *direction* argument can be either :const:`PCM_PLAYBACK` or
+   The *direction* argument can be either :const:`PCM_PLAYBACK` or
    :const:`PCM_CAPTURE`, which is relevant if the mixer can control both
    playback and capture volume. The default value is :const:`PCM_PLAYBACK`
    if the mixer has playback channels, otherwise it is :const:`PCM_CAPTURE`.
 
 
-.. method:: Mixer.setvolume(volume, [channel], [direction])
+.. method:: Mixer.setvolume(volume, channel=MIXER_CHANNEL_ALL, direction=PCM_PLAYBACK, unit=Percent)
 
    Change the current volume settings for this mixer. The *volume* argument
-   controls the new volume setting as an integer percentage.
+   controls the new volume setting as either a percentage or a dB value. Both
+   integer and floating point values can be given.
 
-   If the optional argument *channel* is present, the volume is set
-   only for this channel. This assumes that the mixer can control the
-   volume for the channels independently.
+   The *channel* argument can be used to restrict the channels for which the volume is
+   set. By default, the volume of all channels is adjusted. This assumes that the mixer
+   can control the volume for the channels independently.
 
-   The optional *direction* argument can be either :const:`PCM_PLAYBACK` or
+   The *direction* argument can be either :const:`PCM_PLAYBACK` or
    :const:`PCM_CAPTURE`, which is relevant if the mixer can control both
    playback and capture volume. The default value is :const:`PCM_PLAYBACK`
    if the mixer has playback channels, otherwise it is :const:`PCM_CAPTURE`.
 
+   The *unit* argument determines how the volume value is interpreted, as a prcentage
+   or as a dB value.
+   
 .. method:: Mixer.setmute(mute, [channel])
 
    Sets the mute flag to a new value. The *mute* argument is either 0 for not

mixertest.py

@@ -46,13 +46,17 @@ def show_mixer(name, kwargs):
     print("Capabilities: %s %s" % (' '.join(mixer.volumecap()),
                                    ' '.join(mixer.switchcap())))
     volumes = mixer.getvolume()
-    for i in range(len(volumes)):
-        print("Channel %i volume: %i%%" % (i,volumes[i]))
+    for i, v in enumerate(volumes):
+        print("Channel %i volume: %.02f%%" % (i, v))
+
+    volumes = mixer.getvolume(unit=alsaaudio.dB)
+    for i, v in enumerate(volumes):
+        print("Channel %i volume: %.02fdB" % (i, v))
 
     try:
         mutes = mixer.getmute()
-        for i in range(len(mutes)):
-            if mutes[i]:
+        for i, m in enumerate(mutes):
+            if m:
                 print("Channel %i is muted" % i)
     except alsaaudio.ALSAAudioError:
         # May not support muting
@@ -60,8 +64,8 @@ def show_mixer(name, kwargs):
 
     try:
         recs = mixer.getrec()
-        for i in range(len(recs)):
-            if recs[i]:
+        for i, r in enumerate(recs):
+            if r:
                 print("Channel %i is recording" % i)
     except alsaaudio.ALSAAudioError:
         # May not support recording