#### b_panther_g

##### Audioholic

I thought I understood THD. Then I read this article:

http://www.ampzilla2000.com/thequest1.html

Mr. Bongiorno, the author, states…

“…Before we go on, let’s talk about some numbers so that we have a basis to work with concerning distortion. Virtually everyone relates to distortion numbers incorrectly. For example, if an amplifier had say 1% THD as read on a distortion meter, is it really one percent? Actually, it isn’t. The distortion amounts that are read on a distortion analyzer are in Volts and the ear doesn’t hear Volts, it hears power. So, if we convert the 1% to power we get a totally different perspective. Let’s say a nominal 200 watt per channel amp is producing 1% THD. As read on the analyzer this would be –40dB’s. But –40dB’s in power is 1/10,000th or 20 milliwatts. On the other hand, since the ear’s hearing curve is logarithmic, 40dB’s represents a RATIO of only 16 to 1. In other words, for every doubling (or halving) of the loudness it takes 10 TIMES (or 1/10th) the power. 20dB’s equals 4 times (or 1/4th) and 30dB’s equals 8 times (or 1/8th) and 40dB’s equals 16 times (or 1/16th). Therefore, if you divide 100 by 16 you get, you guessed it, 6.67%. Now that’s a long ways from 1%. You can scale this up or down in either direction and the RATIO of the results will be the same. So when you apply these true numbers to the human hearing curve it is easy to see why anomalies and distortion artifacts that are buried in the noise can be detected by the ear. There is no black magic here. The so-called golden eared types actually can hear this stuff. The descriptions and verbiage associated with this situation may be a whole different can of worms. I have prepared a chart that shows the true relativity of all these factors.

<table width="80%" border="1" bordercolor="#000000">

<tr>

<td width="16%"><div align="center"><strong>THD Reading</strong></div></td>

<td width="7%"><div align="center"><strong>Db’s</strong></div></td>

<td width="18%"><div align="center"><strong>Distortion Power</strong></div></td>

<td width="20%"><div align="center"><strong>Distortion Watts</strong></div></td>

<td width="18%"><div align="center"><strong>Hearing Ratio</strong></div></td>

<td width="21%"><div align="center"><strong>True Distortion</strong></div></td>

</tr>

<tr>

<td><strong>10%</strong></td>

<td><strong>-20</strong></td>

<td><div align="center"><strong>1%</strong></div></td>

<td><strong> 2</strong></td>

<td><strong> 4:1</strong></td>

<td><strong> 25%</strong></td>

</tr>

<tr>

<td><strong>1%</strong></td>

<td><strong>-40</strong></td>

<td><div align="center"><strong>.01%</strong></div></td>

<td><strong>20mW</strong></td>

<td><strong>16:1</strong></td>

<td><strong>6.67%</strong></td>

</tr>

<tr>

<td><strong>.1%</strong></td>

<td><strong>-40</strong></td>

<td><div align="center"><strong>.0001%</strong></div></td>

<td><strong>200uW</strong></td>

<td><strong>64:1</strong></td>

<td><strong>1.56%</strong></td>

</tr>

<tr>

<td><strong>.01%</strong></td>

<td><strong>-80</strong></td>

<td><div align="center"><strong>.000001%</strong></div></td>

<td><strong>2uW</strong></td>

<td><strong> 256:1</strong></td>

<td><strong> .39%</strong></td>

</tr>

<tr>

<td><strong>.001%</strong></td>

<td><strong>-100</strong></td>

<td><div align="center"><strong>.00000001%</strong></div></td>

<td><strong>20nW</strong></td>

<td><strong> 1024:1</strong></td>

<td><strong> .098%</strong></td>

</tr>

<tr>

<td><strong>.0001%</strong></td>

<td><strong>-120</strong></td>

<td><div align="center"><strong>10(-12)</strong></div></td>

<td><strong>200pW</strong></td>

<td><strong> 4096:1</strong></td>

<td> <div align="left"><strong>.024%</strong></div></td>

</tr>

</table>

You will immediately notice the staggering difference between what the distortion meter is reading verses the true distortion numbers. The first line shows that the true distortion is actually 2½ times greater. The second line shows that the distortion is actually 6.67 times greater. The third line shows that the true distortion is really 15.6 times greater. The fourth line shows that the true distortion is actually 390 times greater. And the fifth line shows that the true distortion is actually almost 1000 TIMES greater, etc. It should be quite obvious to everyone now as to the fact that humans CAN hear artifacts down in the mud. Quite simply put, it is the RATIO of loudness factors that determine what we perceive acoustically and not the THD numbers off of the distortion analyzer…”

<table width="80%" border="1" bordercolor="#000000">

<tr>

<td width="16%"><div align="center"><strong>THD Reading</strong></div></td>

<td width="7%"><div align="center"><strong>Db’s</strong></div></td>

<td width="18%"><div align="center"><strong>Distortion Power</strong></div></td>

<td width="20%"><div align="center"><strong>Distortion Watts</strong></div></td>

<td width="18%"><div align="center"><strong>Hearing Ratio</strong></div></td>

<td width="21%"><div align="center"><strong>True Distortion</strong></div></td>

</tr>

<tr>

<td><strong>10%</strong></td>

<td><strong>-20</strong></td>

<td><div align="center"><strong>1%</strong></div></td>

<td><strong> 2</strong></td>

<td><strong> 4:1</strong></td>

<td><strong> 25%</strong></td>

</tr>

<tr>

<td><strong>1%</strong></td>

<td><strong>-40</strong></td>

<td><div align="center"><strong>.01%</strong></div></td>

<td><strong>20mW</strong></td>

<td><strong>16:1</strong></td>

<td><strong>6.67%</strong></td>

</tr>

<tr>

<td><strong>.1%</strong></td>

<td><strong>-40</strong></td>

<td><div align="center"><strong>.0001%</strong></div></td>

<td><strong>200uW</strong></td>

<td><strong>64:1</strong></td>

<td><strong>1.56%</strong></td>

</tr>

<tr>

<td><strong>.01%</strong></td>

<td><strong>-80</strong></td>

<td><div align="center"><strong>.000001%</strong></div></td>

<td><strong>2uW</strong></td>

<td><strong> 256:1</strong></td>

<td><strong> .39%</strong></td>

</tr>

<tr>

<td><strong>.001%</strong></td>

<td><strong>-100</strong></td>

<td><div align="center"><strong>.00000001%</strong></div></td>

<td><strong>20nW</strong></td>

<td><strong> 1024:1</strong></td>

<td><strong> .098%</strong></td>

</tr>

<tr>

<td><strong>.0001%</strong></td>

<td><strong>-120</strong></td>

<td><div align="center"><strong>10(-12)</strong></div></td>

<td><strong>200pW</strong></td>

<td><strong> 4096:1</strong></td>

<td> <div align="left"><strong>.024%</strong></div></td>

</tr>

</table>

You will immediately notice the staggering difference between what the distortion meter is reading verses the true distortion numbers. The first line shows that the true distortion is actually 2½ times greater. The second line shows that the distortion is actually 6.67 times greater. The third line shows that the true distortion is really 15.6 times greater. The fourth line shows that the true distortion is actually 390 times greater. And the fifth line shows that the true distortion is actually almost 1000 TIMES greater, etc. It should be quite obvious to everyone now as to the fact that humans CAN hear artifacts down in the mud. Quite simply put, it is the RATIO of loudness factors that determine what we perceive acoustically and not the THD numbers off of the distortion analyzer…”

If I understand correctly, Mr. Bongiorno states that published THD numbers are misleading. The % THD, as read from a measuring device, represents volts. Since we do not hear in volts, we need to convert those number into what we actually hear. He then has a conversion table (see above).

Is this article true? If so, what of speakers? Do the % THD numbers show what I'm actually hearing or are they the % read off the measureing device.

Thanks for your help.

Later,

B

P.S. Sorry for the weird looking post.