::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact

Unlinking Stereo Channels II

January 10th, 2013
experiment, vsl1818, sound, tech, music, math  [html]
I have stereo channels I want to unlink. Simple linear interpolation turns out not to be the answer, so I need to determine the relationship between gain, pan, and the output levels experimentally. I set up my VSL1818 as:
  smartphone           AB 1818 VSL
+------------+        +-----------+
|  sine wave |        |           |
| generation >--------> in1       |
|     app    |        |      aux3 >-----+
+------------+  +-----> in2       |     |
                |     |      aux4 >--+  |
                |  +--> in3       |  |  |
                |  |  |           |  |  |
                |  |  +-----------+  |  |
                |  +-----------------+  |
                +-----------------------+
The phone generated a tone, which went into input 1 of the mixer. I connected outputs 3 and 4 of the vsl1818 back to inputs 2 and 3. In software I set the mixer to send input 1 to outputs 3 and 4. Then a program I wrote iterated through combinations of gain and pan while measuring the levels of input 2 and 3:
pan %, gain %, left, right
...
30, 60, 165, 143
30, 61, 166, 145
30, 62, 168, 146
30, 63, 170, 147
30, 64, 172, 150
30, 65, 174, 151
30, 66, 175, 153
30, 67, 177, 156
30, 68, 179, 157
...
(full data, 10000 rows)
This is frustrating because of two different sources of nonlinearity. The first is that gain and pan are combined in some way I don't yet understand. The second is that the chosen gain (out) and measured level (in) aren't linear either:

Still, I can look at equivalence classes, combinations of gain and pan that all keep one channel the same while varying the other. Each graph shows all the combinations of gain (red) and pan (blue) that keep one channel at the specified level.

One channel constant at 0 (raw)
One channel constant at 24 (raw)
One channel constant at 65 (raw)
One channel constant at 84 (raw)
One channel constant at 113 (raw)
One channel constant at 131 (raw)
One channel constant at 160 (raw)
One channel constant at 187 (raw)
One channel constant at 221 (raw)
One channel constant at 235 (raw)

My goal is two functions:

  def to_gain_pan(left, right):
     ...
     return gain, pan

  def to_left_right(gain, pan):
     ...
     return left, right
I think I now have the data I need to write these functions, but I'm still not sure what they are.

Comment via: google plus, facebook

Recent posts on blogs I like:

Live the questions now

Here’s some advice that my Godmother, Lynne Caldwell, gave me a few years ago. I found it again the other day and it struck me that at least I understand its wisdom now. She really did get my problem. It feels like he’s speaking directly to me. It’s from …

via Holly Elmore January 23, 2020

International Links: a Revision

In 2011, I wrote a post arguing that international links underperform. I gave examples, using many links nearly all of which have rotted in the 8.5 years since, showing that the ridership on various air and rail city pairs was lower if they were in two di…

via Pedestrian Observations January 22, 2020

Algorithms interviews: theory vs. practice

When I ask people at trendy big tech companies why algorithms quizzes are mandatory, the most common answer I get is something like "we have so much scale, we can't afford to have someone accidentally write an O(n^2) algorithm and bring the site d…

via Posts on Dan Luu January 5, 2020

more     (via openring)

More Posts:


  ::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact