Audacity Forum

• The memory leak discussed in this thread: http://forum.audacityteam.org/viewtopic ... 39&t=75022
  I believe this is the fault of lines 471:

  Code: Select all

          susp->s1 = NULL;

  and 721:

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          susp->s2 = NULL;

  of file add.c. I believe these lines can just be commented out without harm. I believe the bug in the addition of two sounds will happen whenever two sounds are added with snd-add, and the sum is completely evaluated, and one sound outlasts the physical stop of the other sound (by at least one internal block of samples), and this later-ending sound is not otherwise referenced: then it leaks. Note that if you add many sounds with sim or sum, the last two are added with snd-add, and the others accumulated right to left onto that result with more calls to snd-add. Perhaps nobody detected this common occurrence until I wrote effects that cause this to happen many thousands of times?
• The problems with results of snd-xform given to snd-add, with the resulting sound sometimes incorrect in a way dependent on the sequence of the summands, discussed here: http://forum.audacityteam.org/viewtopic ... 39&t=72398
  
  The fault is again in add.c, not in snd-xform. Change line 405 to:

  Code: Select all

              susp->s1->get_next == SND_get_next && susp->s1->stop == MAX_STOP &&

  and analogously at line 650:

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              susp->s2->get_next == SND_get_next && susp->s2->stop == MAX_STOP &&
  

  Those changes will have the effect of disabling some "optimizations" in snd-add for more structure sharing, which were applied incorrectly to sounds that were shortened by snd-xform: the shortening was ignored and the underlying sound sequence copied to its physical stop. A better fix might be written that does not sacrifice sharing in this case, but it would not be as simple.
  
  To see the bug, generate 1 second of a 100Hz wave, do this in Nyquist prompt:

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          (defun extract-global (snd start end)
            (let* ((t0 (snd-t0 snd))
              (result
               (shift-time (snd-xform snd (snd-srate snd) t0 start end 1.0) start)))
              result))
  
      (let* (
  
      (s1 (extract-global s 0.5 0.51))
      (s2 (extract-global s 0.6 0.61))
      (s3 (extract-global s 0.7 0.71))
  
      )
   (sum s3 s2 s1)
  )

  Whereas if you change the result to (sum s1 s2 s3), you get a different (and correct) result, which should just be three isolated samples of the original wave.

Paul L wrote:Is there an official source repository for Nyquist separate from Audacity? So we don't fork the library?

Paul L wrote:What about Xlisp?

Paul L wrote:The problems with results of snd-xform given to snd-add, with the resulting sound sometimes incorrect in a way dependent on the sequence of the summands, discussed here: http://forum.audacityteam.org/viewtopic ... 39&t=72398

The fault is again in add.c, not in snd-xform. Change line 405 to:

Code: Select all
susp->s1->get_next == SND_get_next && susp->s1->stop != MAX_STOP &&



and analogously at line 650:

Code: Select all
susp->s2->get_next == SND_get_next && susp->s2->stop != MAX_STOP &&



Those changes will have the effect of disabling some "optimizations" in snd-add for more structure sharing, which were applied incorrectly to sounds that were shortened by snd-xform: the shortening was ignored and the underlying sound sequence copied to its physical stop. A better fix might be written that does not sacrifice sharing in this case, but it would not be as simple.

To see the bug, generate 1 second of a 100Hz wave, do this in Nyquist prompt:

Code: Select all
(defun extract-global (snd start end)
(let* ((t0 (snd-t0 snd))
(result
(shift-time (snd-xform snd (snd-srate snd) t0 start end 1.0) start)))
result))

(let* (

(s1 (extract-global s 0.5 0.51))
(s2 (extract-global s 0.6 0.61))
(s3 (extract-global s 0.7 0.71))

)
(sum s3 s2 s1)
)



Whereas if you change the result to (sum s1 s2 s3), you get a different (and correct) result, which should just be three isolated samples of the original wave.