# Numpy combine channels

Discussion in 'Python' started by Wanderer, Sep 10, 2012.

1. ### WandererGuest

I have an array generated by audiolab of left and right stereo channels. It looks like [[1,1],[1,2],[2,3]]. I would like to combine the left and right channels to get an array [2,3,5]. Is there a numpy command to do that?

Thanks

Wanderer, Sep 10, 2012

2. ### Nick CashGuest

> I have an array generated by audiolab of left and right stereo
> channels. It looks like [[1,1],[1,2],[2,3]]. I would like to combine
> the left and right channels to get an array [2,3,5]. Is there a numpy
> command to do that?

You may be over-thinking this, and numpy might not be necessary.

A simple solution would be just a quick list comprehension:

stereo_array = [[1, 1], [1, 2], [2, 3]]
mono_array = [l+r for (l, r) in stereo_array]

Thanks,
Nick Cash

Nick Cash, Sep 10, 2012

3. ### WandererGuest

On Monday, September 10, 2012 3:39:11 PM UTC-4, Wanderer wrote:
> I have an array generated by audiolab of left and right stereo channels. It looks like [[1,1],[1,2],[2,3]]. I would like to combine the left and right channels to get an array [2,3,5]. Is there a numpy command to do that?
>
>
>
> Thanks

I figured it out. numpy.sum(array, axis=1).

Wanderer, Sep 10, 2012
4. ### MRABGuest

On 10/09/2012 20:39, Wanderer wrote:
> I have an array generated by audiolab of left and right stereo
> channels. It looks like [[1,1],[1,2],[2,3]]. I would like to combine
> the left and right channels to get an array [2,3,5]. Is there a numpy
> command to do that?
>
>>> import numpy
>>> numpy.array([[1,1],[1,2],[2,3]], dtype="i")

array([[1, 1],
[1, 2],
[2, 3]])
>>> a[:, 0]

array([1, 1, 2])
>>> a[:, 1]

array([1, 2, 3])
>>> a[:, 0] + a[:, 1]

array([2, 3, 5])

But should they be added together to make mono?

Suppose, for example, that both channels have a maximum value. Their
sum would be _twice_ the maximum.

Therefore, I think that it should probably be the average.

>>> (a[:, 0] + a[:, 1]) / 2

array([1, 1, 2])

MRAB, Sep 10, 2012
5. ### WandererGuest

On Monday, September 10, 2012 4:12:40 PM UTC-4, MRAB wrote:
> On 10/09/2012 20:39, Wanderer wrote:
>
> > I have an array generated by audiolab of left and right stereo

>
> > channels. It looks like [[1,1],[1,2],[2,3]]. I would like to combine

>
> > the left and right channels to get an array [2,3,5]. Is there a numpy

>
> > command to do that?

>
> >

>
> >>> import numpy

>
> >>> numpy.array([[1,1],[1,2],[2,3]], dtype="i")

>
> array([[1, 1],
>
> [1, 2],
>
> [2, 3]])
>
> >>> a[:, 0]

>
> array([1, 1, 2])
>
> >>> a[:, 1]

>
> array([1, 2, 3])
>
> >>> a[:, 0] + a[:, 1]

>
> array([2, 3, 5])
>
>
>
> But should they be added together to make mono?
>
>
>
> Suppose, for example, that both channels have a maximum value. Their
>
> sum would be _twice_ the maximum.
>
>
>
> Therefore, I think that it should probably be the average.
>
>
>
> >>> (a[:, 0] + a[:, 1]) / 2

>
> array([1, 1, 2])

I'm decoding morse code. So it's CV dots and dashes.

Wanderer, Sep 10, 2012
6. ### WandererGuest

On Monday, September 10, 2012 4:12:40 PM UTC-4, MRAB wrote:
> On 10/09/2012 20:39, Wanderer wrote:
>
> > I have an array generated by audiolab of left and right stereo

>
> > channels. It looks like [[1,1],[1,2],[2,3]]. I would like to combine

>
> > the left and right channels to get an array [2,3,5]. Is there a numpy

>
> > command to do that?

>
> >

>
> >>> import numpy

>
> >>> numpy.array([[1,1],[1,2],[2,3]], dtype="i")

>
> array([[1, 1],
>
> [1, 2],
>
> [2, 3]])
>
> >>> a[:, 0]

>
> array([1, 1, 2])
>
> >>> a[:, 1]

>
> array([1, 2, 3])
>
> >>> a[:, 0] + a[:, 1]

>
> array([2, 3, 5])
>
>
>
> But should they be added together to make mono?
>
>
>
> Suppose, for example, that both channels have a maximum value. Their
>
> sum would be _twice_ the maximum.
>
>
>
> Therefore, I think that it should probably be the average.
>
>
>
> >>> (a[:, 0] + a[:, 1]) / 2

>
> array([1, 1, 2])

I'm decoding morse code. So it's CV dots and dashes.

Wanderer, Sep 10, 2012
7. ### WandererGuest

On Monday, September 10, 2012 4:14:18 PM UTC-4, Wanderer wrote:
> On Monday, September 10, 2012 4:12:40 PM UTC-4, MRAB wrote:
>
> > On 10/09/2012 20:39, Wanderer wrote:

>
> >

>
> > > I have an array generated by audiolab of left and right stereo

>
> >

>
> > > channels. It looks like [[1,1],[1,2],[2,3]]. I would like to combine

>
> >

>
> > > the left and right channels to get an array [2,3,5]. Is there a numpy

>
> >

>
> > > command to do that?

>
> >

>
> > >

>
> >

>
> > >>> import numpy

>
> >

>
> > >>> numpy.array([[1,1],[1,2],[2,3]], dtype="i")

>
> >

>
> > array([[1, 1],

>
> >

>
> > [1, 2],

>
> >

>
> > [2, 3]])

>
> >

>
> > >>> a[:, 0]

>
> >

>
> > array([1, 1, 2])

>
> >

>
> > >>> a[:, 1]

>
> >

>
> > array([1, 2, 3])

>
> >

>
> > >>> a[:, 0] + a[:, 1]

>
> >

>
> > array([2, 3, 5])

>
> >

>
> >

>
> >

>
> > But should they be added together to make mono?

>
> >

>
> >

>
> >

>
> > Suppose, for example, that both channels have a maximum value. Their

>
> >

>
> > sum would be _twice_ the maximum.

>
> >

>
> >

>
> >

>
> > Therefore, I think that it should probably be the average.

>
> >

>
> >

>
> >

>
> > >>> (a[:, 0] + a[:, 1]) / 2

>
> >

>
> > array([1, 1, 2])

>
>
>
> I'm decoding morse code. So it's CV dots and dashes.

In case anyone is interested, here is the full code.

# morsecode.py
import numpy as np
from scipy.signal import decimate
from pylab import plot
from pylab import show
import os

def movingaverage(interval, window_size):
window = np.ones(int(window_size)) / float(window_size)
return np.convolve(interval, window, 'same')

def wav2morse(resultDir, filename):
""" Convert a wave file to morse code
resultDir: directory for wave file and results
filename: wave file name

"""
data, _fs, _enc = wavread(resultDir + '\\' + filename)
data = np.sum(data, axis=1)
data = np.fabs(data)
data = movingaverage(data, 100)
data = decimate(data, 2)
highcount = 0
lowcount = 0
fileBase, _fileExt = os.path.splitext(filename)
f = open(resultDir + '\\' + fileBase + '.txt', 'w')
for d in data:
if d > 0.3:
if lowcount > 3000:
f.write(' ')
lowcount = 0
highcount += 1
else:
if highcount > 3000:
f.write('-')
elif highcount > 1000:
f.write('.')
highcount = 0
lowcount += 1
f.close()

Wanderer, Sep 10, 2012
8. ### WandererGuest

On Monday, September 10, 2012 4:14:18 PM UTC-4, Wanderer wrote:
> On Monday, September 10, 2012 4:12:40 PM UTC-4, MRAB wrote:
>
> > On 10/09/2012 20:39, Wanderer wrote:

>
> >

>
> > > I have an array generated by audiolab of left and right stereo

>
> >

>
> > > channels. It looks like [[1,1],[1,2],[2,3]]. I would like to combine

>
> >

>
> > > the left and right channels to get an array [2,3,5]. Is there a numpy

>
> >

>
> > > command to do that?

>
> >

>
> > >

>
> >

>
> > >>> import numpy

>
> >

>
> > >>> numpy.array([[1,1],[1,2],[2,3]], dtype="i")

>
> >

>
> > array([[1, 1],

>
> >

>
> > [1, 2],

>
> >

>
> > [2, 3]])

>
> >

>
> > >>> a[:, 0]

>
> >

>
> > array([1, 1, 2])

>
> >

>
> > >>> a[:, 1]

>
> >

>
> > array([1, 2, 3])

>
> >

>
> > >>> a[:, 0] + a[:, 1]

>
> >

>
> > array([2, 3, 5])

>
> >

>
> >

>
> >

>
> > But should they be added together to make mono?

>
> >

>
> >

>
> >

>
> > Suppose, for example, that both channels have a maximum value. Their

>
> >

>
> > sum would be _twice_ the maximum.

>
> >

>
> >

>
> >

>
> > Therefore, I think that it should probably be the average.

>
> >

>
> >

>
> >

>
> > >>> (a[:, 0] + a[:, 1]) / 2

>
> >

>
> > array([1, 1, 2])

>
>
>
> I'm decoding morse code. So it's CV dots and dashes.

In case anyone is interested, here is the full code.

# morsecode.py
import numpy as np
from scipy.signal import decimate
from pylab import plot
from pylab import show
import os

def movingaverage(interval, window_size):
window = np.ones(int(window_size)) / float(window_size)
return np.convolve(interval, window, 'same')

def wav2morse(resultDir, filename):
""" Convert a wave file to morse code
resultDir: directory for wave file and results
filename: wave file name

"""
data, _fs, _enc = wavread(resultDir + '\\' + filename)
data = np.sum(data, axis=1)
data = np.fabs(data)
data = movingaverage(data, 100)
data = decimate(data, 2)
highcount = 0
lowcount = 0
fileBase, _fileExt = os.path.splitext(filename)
f = open(resultDir + '\\' + fileBase + '.txt', 'w')
for d in data:
if d > 0.3:
if lowcount > 3000:
f.write(' ')
lowcount = 0
highcount += 1
else:
if highcount > 3000:
f.write('-')
elif highcount > 1000:
f.write('.')
highcount = 0
lowcount += 1
f.close()

Wanderer, Sep 10, 2012
9. ### AahzGuest

In article <>,
MRAB <> wrote:
>On 10/09/2012 20:39, Wanderer wrote:
>>
>> I have an array generated by audiolab of left and right stereo
>> channels. It looks like [[1,1],[1,2],[2,3]]. I would like to combine
>> the left and right channels to get an array [2,3,5]. Is there a numpy
>> command to do that?

>
>>>> import numpy
>>>> numpy.array([[1,1],[1,2],[2,3]], dtype="i")

>array([[1, 1],
> [1, 2],
> [2, 3]])
>>>> a[:, 0]

>array([1, 1, 2])
>>>> a[:, 1]

>array([1, 2, 3])
>>>> a[:, 0] + a[:, 1]

>array([2, 3, 5])
>
>But should they be added together to make mono?
>
>Suppose, for example, that both channels have a maximum value. Their
>sum would be _twice_ the maximum.
>
>Therefore, I think that it should probably be the average.
>
> >>> (a[:, 0] + a[:, 1]) / 2

>array([1, 1, 2])

I'd actually think it should be the max. Consider a stereo where one
side is playing a booming bass while the other side is playing a rest
note -- should the mono combination be half as loud as as the bass?
--
Aahz () <*> http://www.pythoncraft.com/

"....Normal is what cuts off your sixth finger and your tail..." --Siobhan

Aahz, Nov 10, 2012
10. ### Dave AngelGuest

On 11/09/2012 11:30 PM, Aahz wrote:
> In article <>,
> MRAB <> wrote:
>> <snip>
>>
>> But should they be added together to make mono?
>>
>> Suppose, for example, that both channels have a maximum value. Their
>> sum would be _twice_ the maximum.
>>
>> Therefore, I think that it should probably be the average.
>>
>>>>> (a[:, 0] + a[:, 1]) / 2

>> array([1, 1, 2])

> I'd actually think it should be the max. Consider a stereo where one
> side is playing a booming bass while the other side is playing a rest
> note -- should the mono combination be half as loud as as the bass?

max would sound awful.

The right answer is to add them with weighting, then scale the whole
waveform according to a new calculation of clipping. Just like a mixer,
you have level controls on each input, then an overall gain.

So if the inputs were x and y, the output would be gain *( x_scale * x
+ y_scale * y), but it'd normally be done in two passes, so as to
minimize the places that are clipped, while maximizing the average.
it's also possible to have gain vary across the time axis, like an agc.
But you wouldn't want that as a default, as it'd destroy the dynamics of
a musical piece.

One more consideration. If these are unsigned values (eg. 0 to 255),
then you should adjust both signals by 128 before storing them as signed
could do the algebraic equivalent, but the programming would be much
simpler on signed values.

--

DaveA

Dave Angel, Nov 10, 2012