<div dir="ltr">OK, thanks. Now I understand what "baked in" means. I think we're on the same page. With good encoder and decoder implementation, this can become a post-decode problem. Spotify and R128 suggest it be solved pre-encode which is a reasonable and holistic approach, just not a wholly robust one given current mastering practices.<div><br clear="all"><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr">-kg</div></div></div><br></div></div><br><div class="gmail_quote"><div dir="ltr">On Thu, Oct 11, 2018 at 6:25 PM Bob Katz <<a href="mailto:bobkatz@digido.com">bobkatz@digido.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>Dear Kevin:</p>
<p>Fraunhofer hasn't solved any problem. Robert from Fraunhofer was
just complaining because Ian claimed that the clipping was "baked
in" to the encoder. Which is untrue to the best of my knowledge.
The encoder/decoder are in a closed floating point relationship
and so if you intercept the decode in the floating point domain,
attenuate it and dither it to 24 bits and then send it on to the
DAC or file or whatever, there will be no clipping. <br>
</p>
<p>Subject to reverification as it's been so long I can't grab my
documentation on previous research I did on this issue.</p>
<p><br>
</p>
<p>Bob</p>
<p><br>
</p>
<br>
<div class="m_-3650715814083358354moz-cite-prefix">On 10/11/18 5:59 PM, Kevin Gross wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div dir="ltr">
<div dir="auto">The floating point decoder of course has ample
headroom naturally. You can also design a fixed point
decoder with ample headroom (possibly sacrificing some
resolution). In either case, it doesn't help to have
headroom if you don't do something to avoid clipping
(attenuation, limiting...) before you send the digital
signal to the DAC.</div>
<div dir="auto"><br>
</div>
<div>I want to know more about how Fraunhofer believe they
have solved this problem.</div>
<div dir="auto"><br>
</div>
<div>Kevin</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Mon, Oct 8, 2018, 10:09 AM Grimm | Eelco
<<a href="mailto:eelco@grimmaudio.com" target="_blank">eelco@grimmaudio.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<div>Hi Kevin,</div>
<div><br>
</div>
<div>Interesting point. The question then becomes how
many fixed point based subband decoders are still
around (in percentage of the total). Another question
is whether the path from the decoder to the volume
block (that likely will perform the normalization) is
floating point. </div>
<div><br>
</div>
<div>All the best,</div>
<div>Eelco</div>
<div><br>
<blockquote type="cite">
<div>
<div dir="ltr">I'm pretty sure integer decoders
are still in use. Not on PCs or even smartphones
but in smaller audio appliances (e.g. Bluetooth
speakers). In any case, you've got to get back
to integer at some point to feed the DAC. So you
either give the encoder the extra headroom as
Spotify is suggesting (see Ian's blog) or you
attenuate after the decoder as you've suggested.
Maybe you end up doing both conservatively in
which case you've lost perhaps 6 dB compared to
0 dBFS PCM which is obviously not a small
discrepancy.
<div><br>
<div>
<div>
<div dir="ltr" class="m_-3650715814083358354gmail-m_-6088654959526734537m_-3354649618894086870gmail_signature">
<div dir="ltr">Kevin Gross - AVA
Networks</div>
</div>
</div>
<br>
</div>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Mon, Oct 8, 2018 at 7:45 AM
Bob Katz <<a href="mailto:bobkatz@digido.com" rel="noreferrer" target="_blank">bobkatz@digido.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">
<p>Ian, it's been a while since I performed
this test. I would have to retest to be
sure, but to the best of my recollection,
<b>the clipping is ONLY on the repro side
and only when converted to fixed point.</b>
Remember that all the codecs (both encode
and decode side) are 32 bit floating
point. <br>
</p>
<p>If you run an attenuator in the floating
point domain after the decoder, you can
fix any over issues which would manifest
as clipping when converted to fixed. Test
it yourself. Run Apple's AU lab with the
round trip codec and Bitter placed in
critical places. <br>
</p>
<p>Then put a 24 bit dithering plugin and
run a distortion test on a sine wave to
make sure it's not an illusion. If you
guys don't perform this test before the
weekend, I'll try to do it myself again. <br>
</p>
<p><br>
</p>
<p>Best wishes,<br>
</p>
<p><br>
</p>
<p>Bob</p>
<br>
<div class="m_-3650715814083358354gmail-m_-6088654959526734537m_-3354649618894086870m_-238104789122760974moz-cite-prefix">On
10/7/18 7:39 PM, Ian Shepherd wrote:<br>
</div>
<blockquote type="cite">
<pre>Hi All !
My recent blog post about lossy encode clipping has had quiet a bit of attention:
<a class="m_-3650715814083358354gmail-m_-6088654959526734537m_-3354649618894086870m_-238104789122760974moz-txt-link-freetext" href="http://productionadvice.co.uk/spotify-upload-true-peak/" rel="noreferrer" target="_blank">http://productionadvice.co.uk/spotify-upload-true-peak/</a>
Including an email from Robert Bleidt @ Fraunhofer. He’s asking if I have specific examples of encodes that have “baked in” the clipping, because his position is that it shouldn’t happen, these days.
I’d like to give him a helpful reply and I’ve experienced problems myself in the past with encoding from Logic and Audacity, for example, but the truth is I don’t have a collection of examples on hand to offer him.
Do any of you have recent examples that I can point him at, or know for sure of current encoders that consistently have issues with extremely loud content ?
Thanks for any suggestions,
Ian
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