Re: [AUDITORY] Converting audio file from WAV to MP3 changes file duration. Why? (Hanne Stenzel )


Subject: Re: [AUDITORY] Converting audio file from WAV to MP3 changes file duration. Why?
From:    Hanne Stenzel  <h.stenzel@xxxxxxxx>
Date:    Fri, 17 Nov 2017 09:22:32 +0000
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

--_000_HE1PR0602MB3657967B8687D2E3AE2F37A3C52F0HE1PR0602MB3657_ Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Hello Neeks, If you want to stay with mp3 despite the last two comments, I have understo= od from your email that the zero padding at the start is fixed for the same= codec. Therefore your timestamp should be fine, shouldn't it? You will alw= ays have the same starting offset across all samples. Apart from that, I have conducted reaction time test recently and basically= stumbled over two problems: - to start with, I used key board presses as input into MaxMSP and found, t= hat there was a buffering issue in the range of 20 to 70ms depending on the= setting (as mentioned int he previous email). Yet, with enough data points= collected, I ended up with a similar RT distribution and results as I got = afterwards, having corrected for the buffering. I also read somewhere that = special keys such as alt and ctrl can be handled in real time by the comput= er if that is requested by the software...... - the analysis of the data is not trivial, and I would recommend reading th= is paper "To transform or not to transform: using generalized linear mixed = models to analyse reaction time data" by Lo and Andrews to start with. - from the analysis of my results, differences in the modes of RT distribut= ion of as little as 10 ms may reach significance if there are enough data p= oints. These differences are a lot smaller than any interparticipant differ= ences, or differences you may encounter due to variations in the response s= peed between e.g. left and right hand. Therefore the rather complex statist= ical analysis as outlined in the paper above. Good luck with the tests, Hanne ________________________________ From: AUDITORY - Research in Auditory Perception <AUDITORY@xxxxxxxx>= on behalf of Spencer Russell <sfr@xxxxxxxx> Sent: 16 November 2017 14:33:47 To: AUDITORY@xxxxxxxx Subject: Re: [AUDITORY] Converting audio file from WAV to MP3 changes file = duration. Why? If you're playing in a browser I would also worry about an unknown amount o= f latency caused by the browser and the system audio (probably on the order= of 50-100ms). Are you in control of the computer used for the experiment o= r are you distributing the experiment over the web to be run on subjects' c= omputers (or phones)? -s On Wed, Nov 15, 2017, at 10:03 PM, Neeraj Sharma wrote: Members, Thank you for the suggestions and the useful links. In particular http://lame.sourceforge.net/tech-FAQ.txt states the reason fo= r increase in duration for WAV to MP3. Loosely stating, the increase is due to zero-padding at start and end. The = zero-padding in the start seems to be fixed (for the codec used) but that a= t end will depend on the input file duration (or number of samples). Why this is bothering me is: I have a sound stimuli created in WAV. I have created time stamps to map to= certain significant "waveform events" in the signal. I will be playing back these stimuli in HTML, and due to certain requiremen= t I have to use MP3s. The issue is that: 1. I do not have idea about the MP3 decoder used by the browser to decode t= he MP3s, and hence the duration of audio file will potentially, have some u= nknown alterations. 2. The time-stamps of the same events reported by listening to the stimuli = through browser, will likely always have some (different) offset. Hence, estimating reaction time (as difference in the two timestamps) will = always be overestimated. How much noise (in msec) in reaction time measurement for sound stimuli is = insignificant? Any suggestions on this will help in deciding the relevance = for correcting the offsets. Best regards, Neeks On Wed, Nov 15, 2017 at 5:15 AM, Julien Bloit <julien.bloit@xxxxxxxx<mailt= o:julien.bloit@xxxxxxxx>> wrote: Hi, Zero-padding is applied for filtering purposes, see a (rather old) explanat= ion here: http://lame.sourceforge.net/tech-FAQ.txt A command line tool like "afinfo" will be able to tell you how many valid a= udio frames are in the mp3, and which are the priming and reamainder frames= . Julien On Wed, Nov 15, 2017 at 8:57 AM, Windau, G.R.W. (G=FCnter) <G.Windau@xxxxxxxx= s.ru.nl<mailto:G.Windau@xxxxxxxx>> wrote: Dear Neeks, Your wav audio files can have an arbitrary lenght, depending on the duratio= n of the audio sample. The mp3 audio file however, is a sequence of frames = with a certain length in bytes, and thus also in duration. After going from= wav to mp3 and back, you will see that the the duration of your audio samp= le has changed. I guess there will be some zero padding or small conversion= artifacts before and after the 'real' audio. This may have been designed this way to prevent the introduction of audible= clicks at the beginning and at the end when playing an mp3 file. If you need the duration of your audio files to be maintained, mp3 may not = be what you want. Best wishes, G=FCnter On 15 Nov 2017, at 08:02, Neeraj Sharma <neerajww@xxxxxxxx<mailto:neerajww= @xxxxxxxx>> wrote: Dear Members, An audio file in WAV can be converted to MP3 using following two utilities = in unix terminal (both work, and there may be many more also): $ ffmpeg -i <input.wav> -codec:a libmp3lame -b:a 320k <output.mp3> </dev/nu= ll $ lame -q0 -b128 <input.wav> <output.wav> But the issue is that the duration of <output.mp3> is more than duration of= <input.wav>. This is true with other utilities which I have tried, like so= x. Can anyone give insight on: a. why the duration is increasing? In the attached image below, the duratio= n variation is plotted for 410 sound files. The increase in duration appear= s to be WAV file dependent (although it is within 140ms in this case) b. is there option in the above utilities which can reduce this difference = in duration? I haven't been able to figure this out. Similar issue has been reported by few others also. Example: https://www.sweetwater.com/forums/showthread.php?42631 Best regards, Neeks <duration_var_wav_mp3.png> =97 ing. G=FCnter Windau | Technical Support Group | Dept. Biophysics | Donders= Institute for Brain, Cognition and Behaviour | Radboud University Nijmegen= <https://maps.google.com/?q=3DNijmegen%C2%A0%7C%C2%A0Heyendaalseweg%0D+135,= +NL-6525AJ&entry=3Dgmail&source=3Dg> <https://maps.google.com/?q=3DNijmegen= %C2%A0%7C+%3Chttps://maps.google.com/?q%3DNijmegen%25C2%25A0%257C%25C2%25A0= Heyendaalseweg%250D%2B135,%2BNL-6525AJ%26entry%3Dgmail%26source%3Dg%3E%C2%A= 0Heyendaalseweg%0D+135,+NL-6525AJ&entry=3Dgmail&source=3Dg> |<https://maps.= google.com/?q=3DNijmegen%C2%A0%7C%C2%A0Heyendaalseweg%0D+135,+NL-6525AJ&ent= ry=3Dgmail&source=3Dg> <https://maps.google.com/?q=3DNijmegen%C2%A0%7C+%3Ch= ttps://maps.google.com/?q%3DNijmegen%25C2%25A0%257C%25C2%25A0Heyendaalseweg= %250D%2B135,%2BNL-6525AJ%26entry%3Dgmail%26source%3Dg%3E%C2%A0Heyendaalsewe= g%0D+135,+NL-6525AJ&entry=3Dgmail&source=3Dg> Heyendaalseweg 135, NL-6525AJ= Nijmegen<https://maps.google.com/?q=3DNijmegen%C2%A0%7C+%3Chttps://maps.go= ogle.com/?q%3DNijmegen%25C2%25A0%257C%25C2%25A0Heyendaalseweg%250D%2B135,%2= BNL-6525AJ%26entry%3Dgmail%26source%3Dg%3E%C2%A0Heyendaalseweg%0D+135,+NL-6= 525AJ&entry=3Dgmail&source=3Dg> |<https://maps.google.com/?q=3DNijmegen%C2%= A0%7C+%3Chttps://maps.google.com/?q%3DNijmegen%25C2%25A0%257C%25C2%25A0Heye= ndaalseweg%250D%2B135,%2BNL-6525AJ%26entry%3Dgmail%26source%3Dg%3E%C2%A0Hey= endaalseweg%0D+135,+NL-6525AJ&entry=3Dgmail&source=3Dg> room 00.817 | E: G.= Windau@xxxxxxxx<mailto:G.Windau@xxxxxxxx> | T: +31 24 3613356<tel= :+31%2024%20361%203356> | W: http://www.mbfys.ru.nl/~gunter --_000_HE1PR0602MB3657967B8687D2E3AE2F37A3C52F0HE1PR0602MB3657_ Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable <html> <head> <meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3DWindows-1= 252"> <style type=3D"text/css" style=3D"display:none;"><!-- P {margin-top:0;margi= n-bottom:0;} --></style> </head> <body dir=3D"ltr"> <div id=3D"divtagdefaultwrapper" style=3D"font-size:12pt;color:#000000;font= -family:Calibri,Helvetica,sans-serif;" dir=3D"ltr"> <p></p> <div> <p>Hello Neeks,</p> <p><br> </p> <p>If you want to stay with mp3 despite the last two comments, I have under= stood from your email that the zero padding at the start is fixed for the s= ame codec. Therefore your timestamp should be fine, shouldn't it? You will = always have the same starting offset across all samples.</p> <p><br> </p> <p><br> </p> <p>Apart from that, I have conducted reaction time test recently and basica= lly stumbled over two problems:</p> - to start with, I used key board presses as input into MaxMSP and found, t= hat there was a buffering issue in the range of 20 to 70ms depending on the= setting (as mentioned int he previous email). Yet, with enough data points= collected, I ended up with a similar RT distribution and results as I got afterwards, having corrected for the = buffering. I also read somewhere that special keys such as alt and ctrl can= be handled in real time by the computer if that is requested by the softwa= re......<br> <br> </div> <p>- the analysis of the data is not trivial, and I would recommend reading= this paper &quot;To transform or not to transform: using generalized linea= r mixed models to analyse reaction time data&quot; by Lo and Andrews to sta= rt with. <br> </p> <p><br> </p> <p>- from the analysis of my results, differences in the modes of RT distri= bution of as little as 10 ms may reach significance if there are enough dat= a points. These differences are a lot smaller than any interparticipant dif= ferences, or differences you may encounter due to variations in the response speed between e.g. left and ri= ght hand. Therefore the rather complex statistical analysis as outlined in = the paper above.<br> </p> <p><br> </p> <p>Good luck with the tests,</p> <p>Hanne<br> </p> <p></p> </div> <hr style=3D"display:inline-block;width:98%" tabindex=3D"-1"> <div id=3D"divRplyFwdMsg" dir=3D"ltr"><font face=3D"Calibri, sans-serif" st= yle=3D"font-size:11pt" color=3D"#000000"><b>From:</b> AUDITORY - Research i= n Auditory Perception &lt;AUDITORY@xxxxxxxx&gt; on behalf of Spencer= Russell &lt;sfr@xxxxxxxx&gt;<br> <b>Sent:</b> 16 November 2017 14:33:47<br> <b>To:</b> AUDITORY@xxxxxxxx<br> <b>Subject:</b> Re: [AUDITORY] Converting audio file from WAV to MP3 change= s file duration. Why?</font> <div>&nbsp;</div> </div> <style type=3D"text/css"> <!-- p.x_MsoNormal, p.x_MsoNoSpacing {margin:0} --> </style> <div> <div>If you're playing in a browser I would also worry about an unknown amo= unt of latency caused by the browser and the system audio (probably on the = order of 50-100ms). Are you in control of the computer used for the experim= ent or are you distributing the experiment over the web to be run on subjects' computers (or phones)?<br> </div> <div><br> </div> <div>-s</div> <div><br> </div> <div>On Wed, Nov 15, 2017, at 10:03 PM, Neeraj Sharma wrote:<br> </div> <blockquote type=3D"cite"> <div dir=3D"ltr"> <div>Members,<br> </div> <div><br> </div> <div> <div>Thank you for the suggestions and the useful links.<br> </div> <div> <div>In particular&nbsp;<a href=3D"http://lame.sourceforge.net/tech-FAQ.txt= " style=3D"font-size:12.8px">http://lame.<wbr>sourceforge.net/tech-FAQ.txt<= /a>&nbsp;<wbr>states the reason for increase in duration for WAV to MP3.<br= > </div> <div>Loosely stating, the increase is due to zero-padding at start and end.= The zero-padding in the start seems to be fixed (for the codec used) but t= hat at end will depend on the input file duration (or number of samples).<b= r> </div> <div><br> </div> <div>Why this is bothering me is:<br> </div> <div><br> </div> <div>I have a sound stimuli created in WAV. I have created time stamps to m= ap to certain significant &quot;waveform events&quot; in the signal.<br> </div> <div>I will be playing back these stimuli in HTML, and due to certain requi= rement I have to use MP3s. The issue is that:<br> </div> <div>1. I do not have idea about the MP3 decoder used by the browser to dec= ode the MP3s, and hence the duration of audio file will potentially, have s= ome unknown alterations.<br> </div> <div>2. The time-stamps of the same events reported by listening to the sti= muli through browser, will likely always have some (different) offset.<br> </div> <div>&nbsp;<br> </div> <div>Hence, estimating reaction time (as difference in the two timestamps) = will always be overestimated.<br> </div> <div>How much noise (in msec) in reaction time measurement for&nbsp;sound s= timuli is insignificant? Any suggestions on this will help in deciding the = relevance for correcting the offsets.&nbsp;<br> </div> <div><br> </div> <div>Best regards,<br> </div> <div>Neeks<br> </div> </div> </div> </div> <div> <div><br> </div> <div> <div>On Wed, Nov 15, 2017 at 5:15 AM, Julien Bloit <span dir=3D"ltr">&lt;<a= href=3D"mailto:julien.bloit@xxxxxxxx">julien.bloit@xxxxxxxx</a>&gt;</spa= n> wrote:<br> </div> <blockquote style=3D"margin-top:0px; margin-right:0px; margin-bottom:0px; m= argin-left:0.8ex; border-left-width:1px; border-left-style:solid; border-le= ft-color:rgb(204,204,204); padding-left:1ex"> <div dir=3D"ltr"> <div>Hi,&nbsp;<br> </div> <div> <div><br> </div> <div>Zero-padding is applied for filtering purposes, see a (rather old) exp= lanation here:&nbsp;<br> </div> </div> <div><a href=3D"http://lame.sourceforge.net/tech-FAQ.txt">http://lame.sourc= eforge.net/<wbr>tech-FAQ.txt</a><br> </div> <div><br> </div> <div>A command line tool like &quot;afinfo&quot; will be able to tell you h= ow many valid audio frames are in the mp3, and which are the priming and re= amainder frames.<br> </div> <div><span><span class=3D"x_colour" style=3D"color:rgb(136,136,136)"></span= ></span><br> </div> <div><span><span class=3D"x_colour" style=3D"color:rgb(136,136,136)"></span= ></span><br> </div> <div><span><span class=3D"x_colour" style=3D"color:rgb(136,136,136)">Julien= </span></span><br> </div> <div><span><span class=3D"x_colour" style=3D"color:rgb(136,136,136)"></span= ></span><br> </div> </div> <div> <div> <div> <div><br> </div> <div> <div>On Wed, Nov 15, 2017 at 8:57 AM, Windau, G.R.W. (G=FCnter) <span dir= =3D"ltr">&lt;<a href=3D"mailto:G.Windau@xxxxxxxx">G.Windau@xxxxxxxx= nl</a>&gt;</span> wrote:<br> </div> <blockquote style=3D"margin-top:0px; margin-right:0px; margin-bottom:0px; m= argin-left:0.8ex; border-left-width:1px; border-left-style:solid; border-le= ft-color:rgb(204,204,204); padding-left:1ex"> <div style=3D"word-wrap:break-word"> <div>Dear Neeks, <br> </div> <div><br> </div> <div> <div>Your wav audio files can have an arbitrary lenght, depending on the du= ration of the audio sample. The mp3 audio file however, is a sequence of fr= ames with a certain length in bytes, and thus also in duration. After going= from wav to mp3 and back, you will see that the the duration of your audio sample has changed. I guess there = will be some zero padding or small conversion artifacts before and after th= e 'real' audio.<br> </div> <div><br> </div> <div>This may have been designed this way to prevent the introduction of au= dible clicks at the beginning and at the end when playing an mp3 file.<br> </div> <div><br> </div> <div>If you need the duration of your audio files to be maintained, mp3 may= not be what you want.<br> </div> <div><br> </div> <div>Best wishes,<br> </div> <div>G=FCnter<br> </div> <div><br> </div> <div> <div><br> </div> <blockquote type=3D"cite"> <div> <div> <div>On 15 Nov 2017, at 08:02, Neeraj Sharma &lt;<a href=3D"mailto:neerajww= @xxxxxxxx">neerajww@xxxxxxxx</a>&gt; wrote:<br> </div> <div><br> </div> </div> </div> <div> <div> <div> <div dir=3D"ltr"> <div>Dear Members,<br> </div> <div><br> </div> <div>An audio file in WAV can be converted to MP3 using following two utili= ties in unix terminal (both work, and there may be many more also):<br> </div> <div><br> </div> <div>$ ffmpeg -i &lt;input.wav&gt; -codec:a libmp3lame -b:a 320k &lt;output= .mp3&gt; &lt;/dev/null<br> </div> <div>$ lame -q0 -b128 &lt;input.wav&gt; &lt;output.wav&gt;<br> </div> <div><br> </div> <div>But the issue is that the duration of &lt;output.mp3&gt; is more than = duration of &lt;input.wav&gt;. This is true with other utilities which I ha= ve tried, like sox. Can anyone give insight on:<br> </div> <div><br> </div> <div><br> </div> <div> <div>a. why the duration is increasing? In the attached image below, the du= ration variation is plotted for 410 sound files. The increase in duration a= ppears to be WAV file dependent (although it is within 140ms in this case)<= br> </div> <div><br> </div> <div><br> </div> <div> <div>b. is there option in the above utilities which can reduce this differ= ence in duration?&nbsp; I haven't been able to figure this out.<br> </div> <div><br> </div> <div>Similar issue has been reported by few others also.<br> </div> <div>Example: <a href=3D"https://www.sweetwater.com/forums/showthread.php?4= 2631">https://www.sweetwater.com/for<wbr>ums/showthread.php?42631</a><br> </div> <div><br> </div> <div>Best regards,<br> </div> <div>Neeks <br> </div> <div><br> </div> <div><br> </div> </div> </div> </div> </div> </div> <div><span>&lt;duration_var_wav_mp3.png&gt;</span><br> </div> </div> </blockquote> </div> <div><br> </div> <div> <div style=3D"text-align:start; text-indent:0px; word-wrap:break-word"> <div><span class=3D"x_colour" style=3D"color:rgb(121,121,121)"><span class= =3D"x_font" style=3D"font-family:Verdana,&quot; sans-serif&quot;"><span cla= ss=3D"x_size" style=3D"font-size:11px">=97</span></span></span><br> </div> <div style=3D"color:rgb(0,0,0); letter-spacing:normal; text-transform:none;= white-space:normal; word-spacing:0px"> <span class=3D"x_colour" style=3D"color:rgb(121,121,121)"><span class=3D"x_= font" style=3D"font-family:Calibri,sans-serif"><span class=3D"x_size" style= =3D"font-size:15px"><span class=3D"x_font" style=3D"font-family:Verdana,san= s-serif"><span class=3D"x_size" style=3D"font-size:8pt">ing. 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href=3D"https://maps.google.com/?q= =3DNijmegen%C2%A0%7C&#43;%3Chttps://maps.google.com/?q%3DNijmegen%25C2%25A0= %257C%25C2%25A0Heyendaalseweg%250D%2B135,%2BNL-6525AJ%26entry%3Dgmail%26sou= rce%3Dg%3E%C2%A0Heyendaalseweg%0D&#43;135,&#43;NL-6525AJ&amp;entry=3Dgmail&= amp;source=3Dg">|</a>&nbsp;</span></span></span></span></span><span class= =3D"x_colour" style=3D"color:rgb(121,121,121)"><span class=3D"x_font" style= =3D"font-family:Calibri,sans-serif"><span class=3D"x_size" style=3D"font-si= ze:15px"><span class=3D"x_font" style=3D"font-family:Verdana,sans-serif"><s= pan class=3D"x_size" style=3D"font-size:8pt">room 00.817&nbsp;</span></span></span></span></span><span class=3D"x_colour" st= yle=3D"color:rgb(121,121,121)"><span class=3D"x_font" style=3D"font-family:= Calibri,sans-serif"><span class=3D"x_size" style=3D"font-size:15px"><span c= lass=3D"x_font" style=3D"font-family:Verdana,sans-serif"><span class=3D"x_s= ize" style=3D"font-size:8pt">|</span></span></span></span></span><span clas= s=3D"x_colour" style=3D"color:rgb(121,121,121)"><span class=3D"x_font" styl= e=3D"font-family:Calibri,sans-serif"><span class=3D"x_size" style=3D"font-s= ize:15px"><span class=3D"x_font" style=3D"font-family:Verdana,sans-serif"><= span class=3D"x_size" style=3D"font-size:8pt">&nbsp;E:&nbsp;<a href=3D"mail= to:G.Windau@xxxxxxxx">G.Windau@xxxxxxxx<wbr>u.nl</a>&nbsp;| T: <a href=3D"tel:&#43;31%2024%20361%203356">&#43;31 24 3613356</a>&nbsp;<= /span></span></span></span></span><span class=3D"x_colour" style=3D"color:r= gb(121,121,121)"><span class=3D"x_font" style=3D"font-family:Calibri,sans-s= erif"><span class=3D"x_size" style=3D"font-size:15px"><span class=3D"x_font= " style=3D"font-family:Verdana,sans-serif"><span class=3D"x_size" style=3D"= font-size:8pt">|&nbsp;</span></span><span class=3D"x_font" style=3D"font-fa= mily:Verdana,sans-serif"><span class=3D"x_size" style=3D"font-size:8pt">W:&= nbsp;<a href=3D"http://www.mbfys.ru.nl/~gunter">http://www.mbfys.<wbr>ru.nl= /~gunter</a></span></span></span></span></span><br> </div> </div> </div> </div> </div> </blockquote> </div> </div> </div> </div> </blockquote> </div> </div> </blockquote> <div><br> </div> </div> </body> </html> --_000_HE1PR0602MB3657967B8687D2E3AE2F37A3C52F0HE1PR0602MB3657_--


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Electrical Engineering Dept., Columbia University