<html><head><meta http-equiv="Content-Type" content="text/html charset=iso-8859-1"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">More info about iOS 11 audio.<div><br></div><div>All the best,</div><div>Eelco<br><div><br><div>Begin forwarded message:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; color:rgba(0, 0, 0, 1.0);"><b>From: </b></span><span style="font-family:'Helvetica';">Mikko Lohenoja <<a href="mailto:mikko.lohenoja@yle.fi">mikko.lohenoja@yle.fi</a>><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; color:rgba(0, 0, 0, 1.0);"><b>Subject: </b></span><span style="font-family:'Helvetica';"><b>Re: [FAR-PLOUD] iOS 11 Music app normalisation now uses floating point target</b><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; color:rgba(0, 0, 0, 1.0);"><b>Date: </b></span><span style="font-family:'Helvetica';">7 september 2017 06:58:26 CEST<br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; color:rgba(0, 0, 0, 1.0);"><b>To: </b></span><span style="font-family:'Helvetica';">Eelco Grimm <<a href="mailto:eelco.grimm@hku.nl">eelco.grimm@hku.nl</a>><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; color:rgba(0, 0, 0, 1.0);"><b>Cc: </b></span><span style="font-family:'Helvetica';">"PLOUD (<a href="mailto:far-ploud@list.ebu.ch">far-ploud@list.ebu.ch</a>)" <<a href="mailto:far-ploud@list.ebu.ch">far-ploud@list.ebu.ch</a>><br></span></div><br><div><div dir="ltr">Dear Eelco, dear all,<div><br></div><div>The adjustment of iTunes/iOS Music is visible on a computer via song's "Get Info" tab, it is the iTunes Sound Check adjustment.</div><div><br></div><div>Even though if it can read maximum of +30,0 dB and minimum of -18,2 dB in the info tab, the adjustment actually stays always within -12,00 maximum attenuation and +12,00 maximum boost of the original level, when measured with a level meter. The iOS App uses this same information which is stored in the file metadata. Also music streamed from Apple Music streaming service uses this same method and calculation.</div><div><br></div><div>There is actually an internal real-time limiter in the iPhone, so it is not possible to distort the device, even if the peaks would go over. Therefore it may not be necessary to include this feature in the player, at least in the iOS environment. Currently it is still not possible to use this method in third party apps, or even in the Apple's own Music app without manually changing the normalisation metadata.</div><div><br></div><div>For those who are interested, iTunes Soundcheck metadata consists of 10 values, of which only 4 are used for the adjustment.</div><div><br></div><div>1. Average Perceived Loudness, Left channel (Fixed blocks of 50 ms RMS from file start) in milliwatts (0 dB adjust = 1000, positive adjust < 1000, negative adjust > 1000)</div><div>2. Average Perceived Loudness, Right channel (Fixed blocks of 50 ms RMS from file start) in milliwatts (0 dB adjust = 1000, positive adjust < 1000, negative adjust > 1000)<br></div><div>3. Max Perceived Loudness, Left channel (Single 50 ms RMS block, sliding start point) in milliwatts (same as above)<br></div><div>4. Max Perceived Loudness, Right channel (Single 50 ms RMS block, sliding start point) in milliwatts (same as above)<br></div><div>5. Position of Max Perceived Loudness, Left channel in milliseconds from file start</div><div>6. Position of Max Perceived Loudness, Right channel in milliseconds from file start</div><div><div>7. Max Sample Peak amplitude, Left Channel, range from 0 to 32768</div><div>8. Max Sample Peak amplitude, Right Channel, range from 0 to 32768</div></div><div>9. Position of Max Sample Peak, Left Channel, in milliseconds from file start</div><div>10. Position of Max Sample Peak, Right Channel, in milliseconds from file start</div><div><br></div><div>All values are stored as a single string in 8-digit HEX format in the file metadata but they can be viewed as decimal numbers (not dB values) via Terminal with afinfo command.</div><div><br></div><div>For RMS values 1 to 4, an EQ curve somewhat similar to ISO 223 is used for the frequency weighting.</div><div><br></div><div>The file is adjusted by searching the maximum single value of 1 and 2, and attenuated accordingly if the values 7 or 8 would exceed 0dBfs for wav file extension and -1 dBFS for the m4a file extension (even for Apple Lossless encoding) after the adjustment of 1 and 2.</div><div><br></div><div>The max perceived loudness values (3&4) and the location values (5,6 and 9,10) do not affect the adjustment.</div><div><br></div><div>This test was done by setting the values 7 and 8 to zero, so that the player doesn't attenuate by the sample peak values.</div><div><br></div><div>All the best,</div><div>Mikko</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">2017-09-06 23:58 GMT+03:00 Eelco Grimm <span dir="ltr"><<a href="mailto:eelco.grimm@hku.nl" target="_blank">eelco.grimm@hku.nl</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div>Dear Mikko,</div><div><br></div><div>Great catch!</div><div><br></div><div>Can you explain what you mean with "It is only possible to adjust a file within -12 to +12 dB's."? Which adjustment is that?</div><div><br></div><div>And I figure that your implementation idea would be to just have a +7 dB offset for -23 LUFS material in the streaming app. But of course this will lead to clipping as soon as users turn up the volume and peaks on the original program are louder than -7 dBFS. Mark that I am not sure if this is a very bad thing (it only happens when people play very loud and in that case the ear buds will already distort a lot...), but if possible a limiter would be more elegant.</div><div><br></div><div>All the best,</div><div>Eelco</div><div><br><blockquote type="cite"><span class=""><div dir="ltr"><div>I am running Apple's iOS 11 Beta on my phone, and I discovered that the manufacturer has made a good step in loudness normalisation architecture.</div><div><br></div><div>I have understood that previous versions of the iOS operating system have used fixed point architecture and therefore it was important to not exceed peaks before the device volume control stage. This led to the problem that apps had to run hot if the user volume control was low.</div><div><br></div><div>Now in iOS 11 it is possible to run an overmodulated signal through the dedicated Music app without any distortion, which means there's a floating point architecture.</div><div><br></div><div>There's still a limitation of the adjustment range, and of course the algorithm is still not ITU BS.1770. It is only possible to adjust a file within -12 to +12 dB's. But with a floating point architecture, this is actually not a problem, because you can adjust very quiet material to a louder floating point target than it would have been possible "straight in the file". The range should still be a little wider to cover all the material.</div><div><br></div><div>Music app still addresses the peaks by default, and it is not possible to exceed 0dBFS with its initial setting but it was possible to test this by overwriting the audio file iTunes normalisation metadata which contains the peak and loudness information.</div><div><br></div><div>Let's hope this is a good step for the loudness normalisation in other apps too.</div><div><br></div><div>All the best,</div><div>Mikko</div><div><br></div><div>-- <br><div class="m_3364853502476218840gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div>Mikko Lohenoja<br></div><div>Äänisuunnittelija / Sound Designer</div><div>Yle-Keskus, Mediatalo</div><div>Uutiskatu 5, Helsinki, Finland</div><div>PL 10, 00024 YLEISRADIO</div><div>tel. <a href="tel:+358%2040%206593292" value="+358406593292" target="_blank">+358 406593292</a></div></div></div></div></div></div></div></div></div></div>
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