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Old 16th May 2013, 04:31 AM   #3101
fas42 is online now fas42  Australia
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There is no dynamic compression of the waveform signal in MP3, merely loss of information about some of the subtle elements of the waveform "wriggling". If you can hear dynamic compression then there is a fault in the playback chain -- it's pretty easy to do an experiment of taking a track of extremely dynamic music, compressing it via a high quality encoder, and then decoding that version in software, and comparing the original with the encode/decode generated one. Minimal differences will be seen ...

What can happen is that the process of decoding the MP3 file at the time of playback degrades the quality, by the functioning of the circuitry doing the decoding creating electrical interference. This can be checked by doing the decoding prior to the playback, as a separate activity; I've done this experiment many times, and have always found a very marked improvement occurs
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Old 16th May 2013, 05:28 AM   #3102
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I also find that replaying MP3's with good dynamics to be a different set of challenges than for CD. Either is doable. Either is enjoyable. But they are different--They are not the same signal.

Psycho-acoustic based lossy compression can sound different to different people. I am personally allergic to most, but not all, MP4 types, which give me a headache. Same music from CD or MP3 doesn't cause the headache. So, there is yet more differences. Decoding and playback can be curiously more difficult with some types.
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Old 16th May 2013, 06:06 AM   #3103
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In trying to relate that to audio amplifiers. . . apparently, specs like noise floor and different harmonic distortion types, can either help or hinder the lossy codecs like MP3 and MP4. For usage data concerning harmonics, I see that small signal triodes (and some fet devices) are unusually popular when the source is a lossy codec. Perhaps that is a small clue.
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Old 16th May 2013, 07:48 AM   #3104
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It just so happens that yesterday evening I had a discussion about this with several friends from the AES. Their point was that you should listen to MP3 on a good system with flat frequency response. The MP3 coding assumes a flat replay response, with the ear then doing the nonlinear processing.

If you listen to MP3 on a crappy system you are bound to hear all kinds of artifacts that disappear on a good system.
Was news to me.

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Old 16th May 2013, 10:07 AM   #3105
Waly is offline Waly  United Kingdom
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Originally Posted by davada View Post
All I hear with any MP3 is dynamic compression. I don't see how bit rate can make up for that. I'm not saying they can't sound pleasing but there is no dynamics. Anyone old enough to remember what dynamic recordings sound like I think will agree.
Who am I to debate your subjective evaluation, but I need to mention that "compression" in "dynamic compression" is not the same concept as in "MP3 compression".

Could it be that you were influenced in your evaluation by the misunderstanding of the terminology? Something like "MP3 is compressing, therefore it may lead to some loss of dynamics"? That would be like "silver wiring has a bright silvery sound".
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Old 17th May 2013, 02:21 AM   #3106
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Default MIC compensation

Hi Bob

I'm reading your book inchmeal, I'm using the MIC compensation that works very well for VAS DIFF, but by setting random values would like guidance to set the values, I know that the values ​​depend on the design, looking for something as a proportion "golden rule" for MIC.

Here where you write texts:

Paper - MOSFET power amp:

Feedback compensation is provided by C4 and R3 (RC network), which implement rolloff feedback from the output of the predriver to the inverting amplifier input, establishing a stable gain crossover frequency of about 2 MHz. Providing compensation by feedback to the input stage tends to allow improved slew rate and reduced power supply coupling, the latter because both ends of the network are ground-referenced (in contrast to Miller-effect compensation of Fig. 7). Elements C3 and R4 act to stabilize the loop formed by C4 and R13. This front-end design enables the amplifier to achieve a slew rate in excess of 300 V/us.

Book - Designing Audio Power Amplifiers, Chapter 9

Combining the Best of Input and Miller Compensation
Miller input compensation (MIC) implements input compensation by means of negative feedback to the input stage [1]. It provides many advantages analogous to those that Miller compensation provides over simple shunt lag compensation. Figure 9.7 illustrates an amplifier with Miller input compensation. Instead of routing the compensation capacitor back to the input of the VAS, it is routed all the way back to the input of the IPS. This encloses the input stage in the wideband compensation loop, reducing its
distortion and increasing its dynamic range. For this reason, it breaks the relationship between gain crossover frequency and slew rate. The 50-W amplifier in Ref. 1 achieved a slew rate of 300 V/s using this compensation technique. The gain crossover frequency Fc in this scheme is the frequency where X(C1) = R2. This frequency is set to 500 kHz in Figure 9.7.


From what I understand and based on simulations is that RC network defines the main pole or first pole. MIC improves the rolloff for high frequency, easing some parasite pole. How I do not know to set values ​​for RC MIC, put a ideal curve 6db/8 and set RC MIC of according to the curve 6db/8, but as you can see, can put different combinations RC and reach the same result.

My main question is how to set the Cx (pole Fc) and Rx (zero) and what are the maximum values for each?

Thanks in advance
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Old 17th May 2013, 07:38 AM   #3107
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Quote:
Originally Posted by jan.didden

If you listen to MP3 on a crappy system you are bound to hear all kinds of artifacts that disappear on a good system.
I've found the opposite to be true ! Are we allowed to disagree with AES peeps
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Old 17th May 2013, 09:57 AM   #3108
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Originally Posted by Rafael L View Post
My main question is how to set the Cx (pole Fc) and Rx (zero) and what are the maximum values for each?
Can only be done, as far as I am aware, by simulating the minor loop gain for different values of R and C. Set C=2.2nF and then vary R untill you locate the zero required to give adequate stability margins.

Last edited by michaelkiwanuka; 17th May 2013 at 10:13 AM.
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Old 17th May 2013, 10:11 AM   #3109
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Waly View Post
Who am I to debate your subjective evaluation, but I need to mention that "compression" in "dynamic compression" is not the same concept as in "MP3 compression".

Could it be that you were influenced in your evaluation by the misunderstanding of the terminology? Something like "MP3 is compressing, therefore it may lead to some loss of dynamics"? That would be like "silver wiring has a bright silvery sound".
Can we reproduce a 96dB dynamic range out of a 256Kb/s rate
MP3 file..?..
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Old 17th May 2013, 10:36 AM   #3110
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Quote:
Originally Posted by wahab View Post
Can we reproduce a 96dB dynamic range out of a 256Kb/s rate
MP3 file..?..
Yes.
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