<div style="color:black;font: 12pt Arial, Helvetica, sans-serif;">This data sheet has become the new typical for TI ... I, too, used to respect the company ... but apparently all the analog people have departed. My first experience was with a similar chip in the older TLV320 series. The analog input specs and applications are like a page in a textbook that says "the solution to this problem is left to the reader as an exercise." The data sheet for the PCM6240 is an analog joke! Having recently done a project with electret mics an almost-identical CODEC in a Bluetooth module, I can tell you that the "mic" they talk about is an electret mic. The "load" resistors set the DC operating point of the mic. It's not about power transfer, it's about "bias" (the chip's "bias" output is generally the output of a very low-noise linear regulator (in the Bluetooth module my client chose, made by SiLabs. Buried deep in its 70-page data sheet was advice to not use its internal "bias" regulator make one externally.
<div><br>
</div>
<div>In my experience, the suppliers of cheap electret mics are completely clueless. They'll tell you that supply voltage can be 1.5 to 6 V but that the load resistor should be, say 1 kΩ (with no explanation). In fact, the pins on the mic are the source and drain of the internal FET. In the engineering world, a FET data sheet would list Idss (drain current at zero gate voltage) and maximum drain voltage, among other things. The "recommended" load is chosen for the lowest supply voltage, which also results in the lowest sensitivity for the mic. So I measured the drain current vs voltage for 10 samples to determine Idss = 450 µA and max drain voltage is 7 V for the part. Knowing that, I used a 6 V supply and a load resistor 3 times the value of the "recommended" - which resulted in perfect class A operating point (drain voltage = 1/2 of supply) and a 10 dB increase in sensitivity. Apparently, the manufacturers of these $1 mics think their customers are all just hobbyists and don't want to confuse them with real specs. And TI follows suit in their application notes, again without explanation. Apparently, when an IC has on-board digital processing, the bit-heads get to write the data sheets! I just hope the analog ignorance doesn't leak over into the LTC products ... I have a lot of respect for the innovative engineers there.</div>
<div><br>
</div>
<div>I think, in some cases, we're dealing with the fact that analog design has fallen out of favor with universities and sold students on the idea that "the future is digital" ... but, as AI gets better won't they start writing code? As I used to say in the 80s, "programmers will become the typists of the 21st century."</div>
<div><br>
</div>
<div>Ah, now I feel better ...</div>
<div>Bill Whitlock</div>
<div>Ventura, CA<br>
<br>
<br>
<br>
<div style="font-family:arial,helvetica;font-size:10pt;color:black"><font size="2">-----Original Message-----<br>
From: Dan Lavry via ProAudio <proaudio@bach.pgm.com><br>
To: proaudio@bach.pgm.com<br>
Sent: Mon, Jun 14, 2021 7:48 pm<br>
Subject: Re: [ProAudio] Microphones question<br>
<br>
<div id="yiv9484434567">
<div>
<div>We are talking about audio fiction, so here we go:</div>
<div>A new (year old) TI AD IC, the <span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">PCM6240-Q1</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">, on figure 37 of the data
sheet states:</span></div>
<div><font size="+3"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">Figure</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">37 and Figure</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">38 show </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">how to connect </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">a DC-coupled </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">microphone </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">for a differential</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> and single-ended</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> input,</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">respectively.</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> The</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> value </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">of the external</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> bias </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">resistor,</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">R1, must </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">be appropriately </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">chosen
</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">based</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> upon </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">the</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> microphone </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">impedance. </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">For a differential </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">input,</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">the value </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">of the
external</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> bias </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">resistor </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">is recommended</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> to be</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> used </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">for half of the microphone </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">impedance,</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">whereas </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">for a single-ended </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">input,</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">the external</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> bias</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> resistor </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">is </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">recommended</span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"> to be
the same </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">as the microphone </span><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">impedance.</span></span></font></div>
<div><font size="+3"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">They are advocating matching the load to the mic
output impedance (obviously for maximum power transfer).
That optimal setup is of course only true if the mic could
support such load while "behaving well" (linearly, no
clipping or other issues). <br clear="none">
</span></span></font></div>
<div><font size="+3"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">I do respect TI. It is a good company with good
reputation. So can we sort out facts from fiction? I think
the answer is simple, but I will let you experts debate it
if you wish. I am logging off for now, I am starting to feel
like an old guy talking too much, and this "mic loading" is
a whole other issue...<br clear="none">
</span></span></font></div>
<div><font size="+3"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">Regards</span></span></font></div>
<div><font size="+3"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;">Dan Lavry<br clear="none">
</span></span></font></div>
<div><font size="+3"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"><br clear="none">
</span></span></font></div>
<div><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"><br clear="none">
</span></div>
<div><span dir="ltr" style="font-size:14.6667px;font-family:sans-serif;"><br clear="none">
</span></div>
<div class="yiv9484434567yqt2774439080" id="yiv9484434567yqt46091">
<div class="yiv9484434567moz-cite-prefix">On 6/14/2021 3:48 PM, Bill Whitlock via
ProAudio wrote:<br clear="none">
</div>
<blockquote type="cite">
</blockquote></div>
</div>
<div class="yiv9484434567yqt2774439080" id="yiv9484434567yqt79318">
<div>
<div style="color:black;font:12pt Arial, Helvetica, sans-serif;">The
following article, "11 Myths about Analog Noise Analysis," is a
great read for most of the topics raised in this thread:
<div><br clear="none">
<div><a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-freetext" target="_blank" href="https://www.analog.com/en/technical-articles/11-myths-about-analog-noise-analysis.html#">https://www.analog.com/en/technical-articles/11-myths-about-analog-noise-analysis.html#</a></div>
<div><br clear="none">
</div>
<div>Bill Whitlock</div>
<div><br clear="none">
</div>
<div><br clear="none">
<div style="font-family:arial, helvetica;font-size:10pt;color:black;"><font size="2">-----Original Message-----<br clear="none">
From: Dan Lavry via ProAudio
<a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-rfc2396E" ymailto="mailto:proaudio@bach.pgm.com" target="_blank" href="mailto:proaudio@bach.pgm.com"><proaudio@bach.pgm.com></a><br clear="none">
To: David Josephson <a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-rfc2396E" ymailto="mailto:dlj@josephson.com" target="_blank" href="mailto:dlj@josephson.com"><dlj@josephson.com></a>;
<a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-abbreviated" ymailto="mailto:proaudio@bach.pgm.com" target="_blank" href="mailto:proaudio@bach.pgm.com">proaudio@bach.pgm.com</a><br clear="none">
Sent: Mon, Jun 14, 2021 1:14 pm<br clear="none">
Subject: Re: [ProAudio] Microphones question<br clear="none">
<br clear="none">
</font>
<div id="yiv9484434567">
<div>
<div>Yes, we have to pick our battles. The 150 Ohm
that is talking about has near 0 DC.</div>
<div>But the 6.8K resistor to 48V phantom your mic
is connected to has DC... that is where material
may matter. </div>
<div>Yes, there is more to learn every day...</div>
<div> Regards</div>
<div>Dan Lavry</div>
<div><br clear="none">
</div>
<div><br clear="none">
</div>
<div><br clear="none">
</div>
<div><br clear="none">
</div>
<div id="yiv9484434567composer_signature">
<div style="font-size:85%;color:#575757;">Sent
from Samsung Galaxy smartphone.</div>
</div>
<div><br clear="none">
</div>
<div><br clear="none">
</div>
<div align="left" style="font-size:100%;color:#000000;">
<div class="yiv9484434567yqt7917953232" id="yiv9484434567yqtfd59882">
<div>-------- Original message --------</div>
<div>From: David Josephson via ProAudio
<a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-rfc2396E" ymailto="mailto:proaudio@bach.pgm.com" target="_blank" href="mailto:proaudio@bach.pgm.com"><proaudio@bach.pgm.com></a> </div>
<div>Date: 6/14/21 12:11 PM (GMT-08:00) </div>
<div>To: <a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-abbreviated" ymailto="mailto:proaudio@bach.pgm.com" target="_blank" href="mailto:proaudio@bach.pgm.com">proaudio@bach.pgm.com</a> </div>
<div>Subject: Re: [ProAudio] Microphones
question </div>
<div><br clear="none">
</div>
</div>
</div>
<div class="yiv9484434567yqt7917953232" id="yiv9484434567yqtfd98857">The microphone
measurement standard recommends the use of
A-weighted rms <br clear="none">
noise specifications in addition to ITU-R
BS.468-4, which specifies not <br clear="none">
only a frequency weighting curve but a quasi-peak
detector which <br clear="none">
penalizes for low frequency pops and clicks, which
can be a factor for <br clear="none">
some poorly executed microphone designs.<br clear="none">
<br clear="none">
Yes, even some of the experts in the standards
world talk about "low <br clear="none">
noise" resistors. We have to pick our battles.<br clear="none">
<br clear="none">
On 6/14/2021 12:01 PM, Dan Lavry via ProAudio
wrote:<br clear="none">
> Excess noise is important in some cases, and
it is material dependent. I <br clear="none">
> agree that the 150 for the noise measurement
can be "any: 150 Ohm.<br clear="none">
> <br clear="none">
> Regarding "A weighting", I just publish both
figures. In most cases it <br clear="none">
> is 2dB difference.<br clear="none">
> <br clear="none">
> Regards<br clear="none">
> <br clear="none">
> Dan Lavry<br clear="none">
> <br clear="none">
> On 6/14/2021 11:03 AM, Bill Whitlock via
ProAudio wrote:<br clear="none">
>> Dan, I'm glad you caught that one!
Noise is a "stand alone" that <br clear="none">
>> needs no reference except a unit of
measure - and, as frequently <br clear="none">
>> omitted by marketing types, a stated
bandwidth. And I have no problem <br clear="none">
>> in using weighted figures as long as it's
clearly stated.<br clear="none">
>><br clear="none">
>> In my mind, the biggest barrier to
understanding noise and its <br clear="none">
>> implications is the lies, distortions,
and half-truths perpetrated by <br clear="none">
>> marketing folks! A measurement, with
test conditions and references <br clear="none">
>> fully disclosed, is not subject to
interpretation. Sadly, many folks <br clear="none">
>> are "educated" by such misleading
information and will believe, for <br clear="none">
>> example, that the 150 Ω resistor used for
testing preamp noise must be <br clear="none">
>> a special "low-noise" resistor. In fact,
thermal noise has no <br clear="none">
>> dependence on the resistive material at
all. So-called "low-noise" <br clear="none">
>> resistors are low in "excess noise" that
occurs when DC current flows <br clear="none">
>> in it - and there's a huge difference
among those! Anyone whose ever <br clear="none">
>> heard me lecture is well aware that no
love is lost between me and <br clear="none">
>> marketing people.<br clear="none">
>><br clear="none">
>> Bill Whitlock<br clear="none">
>><br clear="none">
>><br clear="none">
>> -----Original Message-----<br clear="none">
>> From: Dan Lavry via ProAudio
<a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-rfc2396E" ymailto="mailto:proaudio@bach.pgm.com" target="_blank" href="mailto:proaudio@bach.pgm.com"><proaudio@bach.pgm.com></a><br clear="none">
>> To: Mike Rivers <a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-rfc2396E" ymailto="mailto:mm1100@yahoo.com" target="_blank" href="mailto:mm1100@yahoo.com"><mm1100@yahoo.com></a>;
<a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-abbreviated" ymailto="mailto:proaudio@bach.pgm.com" target="_blank" href="mailto:proaudio@bach.pgm.com">proaudio@bach.pgm.com</a><br clear="none">
>> Sent: Mon, Jun 14, 2021 9:27 am<br clear="none">
>> Subject: Re: [ProAudio] Microphones
question<br clear="none">
>><br clear="none">
>> I think you are confusing things. EIN
does not need to be measured at <br clear="none">
>> full scale, and it is a real
representative of the noise contributions.<br clear="none">
>><br clear="none">
>> Micpre noise is low and not easy to
measure directly. Say you test <br clear="none">
>> system can measure down to 1uV, but your
signal is 0.1uV. It would be <br clear="none">
>> difficult to measure the noise directly.
Say you set the gain at <br clear="none">
>> 60dB, the noise will become 100uV, and a
1uV system can measure that. <br clear="none">
>> At 40dB gain you get 10uV, still good
enough to measure. In the first <br clear="none">
>> case Ein is 100uV/1000, in the second
case 10UV/100, both yield 0.1uV <br clear="none">
>> which is the real input noise.<br clear="none">
>><br clear="none">
>> Of course that will not hold if the
design is poor. Any reasonable <br clear="none">
>> design will yield very similar ein at
60dB and 40db.<br clear="none">
>><br clear="none">
>> Regards<br clear="none">
>> Dan Lavry<br clear="none">
>><br clear="none">
>><br clear="none">
>><br clear="none">
>><br clear="none">
>> Sent from Samsung Galaxy smartphone.<br clear="none">
>><br clear="none">
>><br clear="none">
>> -------- Original message --------<br clear="none">
>> From: Mike Rivers via ProAudio
<a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-rfc2396E" ymailto="mailto:proaudio@bach.pgm.com" target="_blank" href="mailto:proaudio@bach.pgm.com"><proaudio@bach.pgm.com></a><br clear="none">
>> Date: 6/14/21 8:07 AM (GMT-08:00)<br clear="none">
>> To: <a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-abbreviated" ymailto="mailto:proaudio@bach.pgm.com" target="_blank" href="mailto:proaudio@bach.pgm.com">proaudio@bach.pgm.com</a><br clear="none">
>> Subject: Re: [ProAudio] Microphones
question<br clear="none">
>><br clear="none">
>> How about a little discussion on the
value of knowing the EIN of a <br clear="none">
>> preamp and how the figure is useful to
the designer?<br clear="none">
>><br clear="none">
>> Here's why I ask:<br clear="none">
>><br clear="none">
>> When I was writing reviews regularly, EIN
was (and still is) often <br clear="none">
>> quoted in the product's specs. The
numbers ranged from -125 dBu (just <br clear="none">
>> a couple) to a majority being either -127
or -128 dBu. Manufacturers <br clear="none">
>> liked to tout it because it was a nice
low number with "noise" in its <br clear="none">
>> name. And it was always measured at a
level within a dB or so of <br clear="none">
>> clipping since that's it looked the best.<br clear="none">
>><br clear="none">
>> But unless I missed the appropriate
chapter, EIN is a calculated value <br clear="none">
>> - the measured noise level with the gain
subtracted out. So a preamp <br clear="none">
>> with 60 dB of gain that advertised
EIN=-128 dBu could be expected to <br clear="none">
>> put out -68 dBu of noise, measured, of
course to the advantage of the <br clear="none">
>> marketing department with the appropriate
input termination (0, 100, <br clear="none">
>> or 150 ohms usually) and output load.<br clear="none">
>><br clear="none">
>> So, among design engineers, what's the
big deal about EIN? Is there a <br clear="none">
>> better way of measuring it that's more
meaningful? And if you can <br clear="none">
>> squeeze another dB of EIN out of a
design, how significant will this <br clear="none">
>> be to the user? I<br clear="none">
>><br clear="none">
>> , know "it depends."<br clear="none">
>><br clear="none">
>> -- <br clear="none">
>> For a good time
callhttp://mikeriversaudio.wordpress.com
<a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-rfc2396E" target="_blank" href="http://mikeriversaudio.wordpress.com/"><http://mikeriversaudio.wordpress.com/></a><br clear="none">
>>
_______________________________________________<br clear="none">
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>>
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>>
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ProAudio mailing list<br clear="none">
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<div class="yiv9484434567yqt7917953232" id="yiv9484434567yqtfd17519">_______________________________________________<br clear="none">
ProAudio mailing list<br clear="none">
<a rel="nofollow noopener noreferrer" shape="rect" ymailto="mailto:ProAudio@bach.pgm.com" target="_blank" href="mailto:ProAudio@bach.pgm.com">ProAudio@bach.pgm.com</a><br clear="none">
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<pre class="yiv9484434567moz-quote-pre">_______________________________________________
ProAudio mailing list
<a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-abbreviated" ymailto="mailto:ProAudio@bach.pgm.com" target="_blank" href="mailto:ProAudio@bach.pgm.com">ProAudio@bach.pgm.com</a>
<a rel="nofollow noopener noreferrer" shape="rect" class="yiv9484434567moz-txt-link-freetext" target="_blank" href="http://bach.pgm.com/mailman/listinfo/proaudio">http://bach.pgm.com/mailman/listinfo/proaudio</a>
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<div class="yqt2774439080" id="yqt80081">_______________________________________________<br clear="none">ProAudio mailing list<br clear="none"><a shape="rect" ymailto="mailto:ProAudio@bach.pgm.com" href="mailto:ProAudio@bach.pgm.com">ProAudio@bach.pgm.com</a><br clear="none"><a shape="rect" href="http://bach.pgm.com/mailman/listinfo/proaudio" target="_blank">http://bach.pgm.com/mailman/listinfo/proaudio</a><br clear="none"></div>
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