Re: Possible bug in WAV export

*To*: mathgroup at smc.vnet.net*Subject*: [mg87838] Re: Possible bug in WAV export*From*: m.r at inbox.ru*Date*: Fri, 18 Apr 2008 02:41:17 -0400 (EDT)*References*: <ftsd0o$ba7$1@smc.vnet.net> <ftv8on$7kv$1@smc.vnet.net>

On Apr 15, 4:51 am, Szabolcs <szhor... at gmail.com> wrote: > On Apr 14, 11:39 am, Jerry <Jer75... at yahoo.com> wrote: > > > The sound in Mathematica and the sound from the exported WAV file > > (using some unknown player) seem the same to me. I'm using > > V6.02 on a XP box. > > I experimented some more and it turns out that the problem is not > limited to WAV (it is present with FLAC and AIFF too). However, the > problem only appears randomly, and not in each evaluation. The > following command does not always give the same result: > > ImportString[ > ExportString[ > Play[Sum[Sin[2 Pi 440 k t], {k, 1, 4}], {t, 0, 1}, > SampleRate -> 44100, SampleDepth -> 16], "WAV"], "WAV"] > > In about 20 or so evaluations I always get a few incorrect results. > It is not even necessary to play the sound---it is possible to see the > difference by looking at the spectra: > > Table[ImportString[ > ExportString[ > Play[Sum[Sin[2 Pi 440 k t], {k, 1, 4}], {t, 0, 1}, > SampleRate -> 44100, SampleDepth -> 16], "WAV"], "WAV"], > {20}] > > Can anyone else reproduce this problem? It is very strange that the > result is not deterministic. Any ideas why this might happen? > > To demonstrate that this unbelievable thing really happens, here's an > another example, together with the result. Note that the very same > command returns different results in subsequent evaluations: > > In[1]:= > Table[ > Total[#[[1, 1, 1]]] &@ > ImportString[ > ExportString[ > Play[Sum[Sin[2 Pi 440 k t], {k, 1, 4}], {t, 0, 1}, > SampleRate -> 44100, SampleDepth -> 16], "WAV"], "WAV"], > {20}] > > Out[1]= {0., 268.745, -0.752563, -0.756226, -0.756226, -2.99866, 0., \ > 0., -2.98279, 0., 0.756226, 341.993, 0., -0.752563, 0., 268.017, \ > -0.752563, 0., -2.2522, 0.} > > The small fluctuations could be explained by dithering, but any > reasonably precise result cannot have a sum of 342! The sound > function was constructed in such a way that the sum should be 0. A workaround is to use PlayRange -> All. Maxim Rytin m.r at inbox.ru