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#161
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DSD Recording Good. PCM recordings bad?
"Robert Stanton" wrote in message
m chung wrote in message news:4844a$402154da$c247604 To test your theory, all you need to do is to measure THD of, say a 1KHz signal at various output levels, with and without ultrasonic noise. Do you seriously believe the THD will be less if the noise is present? If the system is acting like it is quantized, and if that ultrasonic noise acts as dither, it is a theoretical and observable fact that a properly-dithered quantized system has zero nonlinear distortion. I would have to verify this with actual measurements, but just from a theoretical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. I've verified it with practical measurements... You can do experiments like this with good DAW software like Audition. It may be only a small improvement. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Agreed. Hysteresis is a memory effect, and it's very different from cross-over distortion. Add enough dither to swamp it, and nonlinear distortion due to it is history. The mechanism is different but the principle is the same. Bias moves the operating curve of tape, to a more linear portion of its' range. Agreed. |
#162
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DSD Recording Good. PCM recordings bad?
"Robert Stanton" wrote in message
m chung wrote in message news:817ac$402130d0$c247604 Your statement implys that linear op-amps are not available. No, my statement implies that it is non-trivial to design an active filter with 120 dB linearity. 120 dB = 0.0001% THD. As close as I've seen it - 0.00015% THD+N for two stages including D-A & A-D: http://www.pcavtech.com/soundcards/LynxTWO/index.htm Looking at the pictures... Second and Third harmonics are about 130 dB below peak operating level, and the rest of the harmonics are at least 10 dB below that. If op-amps with better than 120 dB linearity are available, what is the problem? No practical problem given that -80 dB nonlinear distortion generally suffices for audibly transparent operation. Are you saying the capacitors used would cause non-linearity? If they are unbiased electrolytics... This test had at least 2 electrolytics in series with the signal path. BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) My recollection is that the LynxTWO uses OPA27s in a balanced configuration. The measurements shown were made someplace around +4 dBu. So, each half of the input and output stages were running around -2 dBu which is about 0.5 volt rms. |
#163
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DSD Recording Good. PCM recordings bad?
"Robert Stanton" wrote in message
m chung wrote in message news:817ac$402130d0$c247604 Your statement implys that linear op-amps are not available. No, my statement implies that it is non-trivial to design an active filter with 120 dB linearity. 120 dB = 0.0001% THD. As close as I've seen it - 0.00015% THD+N for two stages including D-A & A-D: http://www.pcavtech.com/soundcards/LynxTWO/index.htm Looking at the pictures... Second and Third harmonics are about 130 dB below peak operating level, and the rest of the harmonics are at least 10 dB below that. If op-amps with better than 120 dB linearity are available, what is the problem? No practical problem given that -80 dB nonlinear distortion generally suffices for audibly transparent operation. Are you saying the capacitors used would cause non-linearity? If they are unbiased electrolytics... This test had at least 2 electrolytics in series with the signal path. BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) My recollection is that the LynxTWO uses OPA27s in a balanced configuration. The measurements shown were made someplace around +4 dBu. So, each half of the input and output stages were running around -2 dBu which is about 0.5 volt rms. |
#164
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DSD Recording Good. PCM recordings bad?
"Robert Stanton" wrote in message
m chung wrote in message news:817ac$402130d0$c247604 Your statement implys that linear op-amps are not available. No, my statement implies that it is non-trivial to design an active filter with 120 dB linearity. 120 dB = 0.0001% THD. As close as I've seen it - 0.00015% THD+N for two stages including D-A & A-D: http://www.pcavtech.com/soundcards/LynxTWO/index.htm Looking at the pictures... Second and Third harmonics are about 130 dB below peak operating level, and the rest of the harmonics are at least 10 dB below that. If op-amps with better than 120 dB linearity are available, what is the problem? No practical problem given that -80 dB nonlinear distortion generally suffices for audibly transparent operation. Are you saying the capacitors used would cause non-linearity? If they are unbiased electrolytics... This test had at least 2 electrolytics in series with the signal path. BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) My recollection is that the LynxTWO uses OPA27s in a balanced configuration. The measurements shown were made someplace around +4 dBu. So, each half of the input and output stages were running around -2 dBu which is about 0.5 volt rms. |
#165
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DSD Recording Good. PCM recordings bad?
"Robert Stanton" wrote in message
m chung wrote in message news:817ac$402130d0$c247604 Your statement implys that linear op-amps are not available. No, my statement implies that it is non-trivial to design an active filter with 120 dB linearity. 120 dB = 0.0001% THD. As close as I've seen it - 0.00015% THD+N for two stages including D-A & A-D: http://www.pcavtech.com/soundcards/LynxTWO/index.htm Looking at the pictures... Second and Third harmonics are about 130 dB below peak operating level, and the rest of the harmonics are at least 10 dB below that. If op-amps with better than 120 dB linearity are available, what is the problem? No practical problem given that -80 dB nonlinear distortion generally suffices for audibly transparent operation. Are you saying the capacitors used would cause non-linearity? If they are unbiased electrolytics... This test had at least 2 electrolytics in series with the signal path. BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) My recollection is that the LynxTWO uses OPA27s in a balanced configuration. The measurements shown were made someplace around +4 dBu. So, each half of the input and output stages were running around -2 dBu which is about 0.5 volt rms. |
#166
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:4844a$402154da$c247604 To test your theory, all you need to do is to measure THD of, say a 1KHz signal at various output levels, with and without ultrasonic noise. Do you seriously believe the THD will be less if the noise is present? I would have to verify this with actual measurements, You do that. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. Hysteresis is a memory effect, and it's very different from cross-over distortion. The mechanism is different but the prinicple is the same. Mechanism different = principle different. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. Bob Stanton |
#167
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:4844a$402154da$c247604 To test your theory, all you need to do is to measure THD of, say a 1KHz signal at various output levels, with and without ultrasonic noise. Do you seriously believe the THD will be less if the noise is present? I would have to verify this with actual measurements, You do that. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. Hysteresis is a memory effect, and it's very different from cross-over distortion. The mechanism is different but the prinicple is the same. Mechanism different = principle different. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. Bob Stanton |
#168
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:4844a$402154da$c247604 To test your theory, all you need to do is to measure THD of, say a 1KHz signal at various output levels, with and without ultrasonic noise. Do you seriously believe the THD will be less if the noise is present? I would have to verify this with actual measurements, You do that. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. Hysteresis is a memory effect, and it's very different from cross-over distortion. The mechanism is different but the prinicple is the same. Mechanism different = principle different. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. Bob Stanton |
#169
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:4844a$402154da$c247604 To test your theory, all you need to do is to measure THD of, say a 1KHz signal at various output levels, with and without ultrasonic noise. Do you seriously believe the THD will be less if the noise is present? I would have to verify this with actual measurements, You do that. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. Hysteresis is a memory effect, and it's very different from cross-over distortion. The mechanism is different but the prinicple is the same. Mechanism different = principle different. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. Bob Stanton |
#170
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote: chung wrote in message news:817ac$402130d0$c247604 Your statement implys that linear op-amps are not available. No, my statement implies that it is non-trivial to design an active filter with 120 dB linearity. 120 dB = 0.0001% THD. If op-amps with better than 120 dB linearity are available, what is the problem? Are you saying the capacitiors used would cause non-linearity? Please read what I said: "It is non-trivial to design an active filter with 120 dB linearity". Bob Stanton BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. |
#171
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote: chung wrote in message news:817ac$402130d0$c247604 Your statement implys that linear op-amps are not available. No, my statement implies that it is non-trivial to design an active filter with 120 dB linearity. 120 dB = 0.0001% THD. If op-amps with better than 120 dB linearity are available, what is the problem? Are you saying the capacitiors used would cause non-linearity? Please read what I said: "It is non-trivial to design an active filter with 120 dB linearity". Bob Stanton BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. |
#172
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote: chung wrote in message news:817ac$402130d0$c247604 Your statement implys that linear op-amps are not available. No, my statement implies that it is non-trivial to design an active filter with 120 dB linearity. 120 dB = 0.0001% THD. If op-amps with better than 120 dB linearity are available, what is the problem? Are you saying the capacitiors used would cause non-linearity? Please read what I said: "It is non-trivial to design an active filter with 120 dB linearity". Bob Stanton BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. |
#173
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote: chung wrote in message news:817ac$402130d0$c247604 Your statement implys that linear op-amps are not available. No, my statement implies that it is non-trivial to design an active filter with 120 dB linearity. 120 dB = 0.0001% THD. If op-amps with better than 120 dB linearity are available, what is the problem? Are you saying the capacitiors used would cause non-linearity? Please read what I said: "It is non-trivial to design an active filter with 120 dB linearity". Bob Stanton BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. |
#174
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DSD Recording Good. PCM recordings bad?
chung wrote in message news:dd41e$40369df3$c247604
BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. It sounds like you are saying there are no op-amps with 120 db linearity. I would find that easy to believe. Maybe we should confine discussion to realistic distortion specificatations. Bob Stanton |
#175
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DSD Recording Good. PCM recordings bad?
chung wrote in message news:dd41e$40369df3$c247604
BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. It sounds like you are saying there are no op-amps with 120 db linearity. I would find that easy to believe. Maybe we should confine discussion to realistic distortion specificatations. Bob Stanton |
#176
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DSD Recording Good. PCM recordings bad?
chung wrote in message news:dd41e$40369df3$c247604
BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. It sounds like you are saying there are no op-amps with 120 db linearity. I would find that easy to believe. Maybe we should confine discussion to realistic distortion specificatations. Bob Stanton |
#177
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DSD Recording Good. PCM recordings bad?
chung wrote in message news:dd41e$40369df3$c247604
BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. It sounds like you are saying there are no op-amps with 120 db linearity. I would find that easy to believe. Maybe we should confine discussion to realistic distortion specificatations. Bob Stanton |
#178
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DSD Recording Good. PCM recordings bad?
chung wrote in message news:dfbb6$40369db0$c247604
I would have to verify this with actual measurements, You do that. Yes, I will and I will post the results, good or bad. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. I see that you do not expect noise to reduce crossover distortion. It is very possible that you are right. The difference between you and me is, I have thought of something new, and I will try it to see if it works. You on the other hand, reject the idea because it is outside of your range of experience. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. That is a big "if". You are not getting more noise, that noise is already there on SACD outputs. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. As the old Wendy's ad said: "parts is parts". Distortion is distortion, whether it is caused by the non-linearity of magnetic tape or by the non-linearity of semiconductors. The linearity curve of unbiased mngnet tape looks very much like the curve of an unbiased push-pull stage. Bob Stanton |
#179
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DSD Recording Good. PCM recordings bad?
chung wrote in message news:dfbb6$40369db0$c247604
I would have to verify this with actual measurements, You do that. Yes, I will and I will post the results, good or bad. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. I see that you do not expect noise to reduce crossover distortion. It is very possible that you are right. The difference between you and me is, I have thought of something new, and I will try it to see if it works. You on the other hand, reject the idea because it is outside of your range of experience. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. That is a big "if". You are not getting more noise, that noise is already there on SACD outputs. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. As the old Wendy's ad said: "parts is parts". Distortion is distortion, whether it is caused by the non-linearity of magnetic tape or by the non-linearity of semiconductors. The linearity curve of unbiased mngnet tape looks very much like the curve of an unbiased push-pull stage. Bob Stanton |
#180
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DSD Recording Good. PCM recordings bad?
chung wrote in message news:dfbb6$40369db0$c247604
I would have to verify this with actual measurements, You do that. Yes, I will and I will post the results, good or bad. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. I see that you do not expect noise to reduce crossover distortion. It is very possible that you are right. The difference between you and me is, I have thought of something new, and I will try it to see if it works. You on the other hand, reject the idea because it is outside of your range of experience. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. That is a big "if". You are not getting more noise, that noise is already there on SACD outputs. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. As the old Wendy's ad said: "parts is parts". Distortion is distortion, whether it is caused by the non-linearity of magnetic tape or by the non-linearity of semiconductors. The linearity curve of unbiased mngnet tape looks very much like the curve of an unbiased push-pull stage. Bob Stanton |
#181
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DSD Recording Good. PCM recordings bad?
chung wrote in message news:dfbb6$40369db0$c247604
I would have to verify this with actual measurements, You do that. Yes, I will and I will post the results, good or bad. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. I see that you do not expect noise to reduce crossover distortion. It is very possible that you are right. The difference between you and me is, I have thought of something new, and I will try it to see if it works. You on the other hand, reject the idea because it is outside of your range of experience. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. That is a big "if". You are not getting more noise, that noise is already there on SACD outputs. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. As the old Wendy's ad said: "parts is parts". Distortion is distortion, whether it is caused by the non-linearity of magnetic tape or by the non-linearity of semiconductors. The linearity curve of unbiased mngnet tape looks very much like the curve of an unbiased push-pull stage. Bob Stanton |
#182
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:dfbb6$40369db0$c247604 I would have to verify this with actual measurements, You do that. Yes, I will and I will post the results, good or bad. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. I see that you do not expect noise to reduce crossover distortion. It is very possible that you are right. The difference between you and me is, I have thought of something new, and I will try it to see if it works. You on the other hand, reject the idea because it is outside of your range of experience. The difference is that you have not thought through your idea carefully. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. That is a big "if". You are not getting more noise, that noise is already there on SACD outputs. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. As the old Wendy's ad said: "parts is parts". Distortion is distortion, whether it is caused by the non-linearity of magnetic tape or by the non-linearity of semiconductors. That's interesting. So you are saying cross-over distortion is the same as clipping distortion? Or jitter distortion? The linearity curve of unbiased mngnet tape looks very much like the curve of an unbiased push-pull stage. Which part of "memory effect" do you have trouble understanding? |
#183
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:dfbb6$40369db0$c247604 I would have to verify this with actual measurements, You do that. Yes, I will and I will post the results, good or bad. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. I see that you do not expect noise to reduce crossover distortion. It is very possible that you are right. The difference between you and me is, I have thought of something new, and I will try it to see if it works. You on the other hand, reject the idea because it is outside of your range of experience. The difference is that you have not thought through your idea carefully. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. That is a big "if". You are not getting more noise, that noise is already there on SACD outputs. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. As the old Wendy's ad said: "parts is parts". Distortion is distortion, whether it is caused by the non-linearity of magnetic tape or by the non-linearity of semiconductors. That's interesting. So you are saying cross-over distortion is the same as clipping distortion? Or jitter distortion? The linearity curve of unbiased mngnet tape looks very much like the curve of an unbiased push-pull stage. Which part of "memory effect" do you have trouble understanding? |
#184
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:dfbb6$40369db0$c247604 I would have to verify this with actual measurements, You do that. Yes, I will and I will post the results, good or bad. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. I see that you do not expect noise to reduce crossover distortion. It is very possible that you are right. The difference between you and me is, I have thought of something new, and I will try it to see if it works. You on the other hand, reject the idea because it is outside of your range of experience. The difference is that you have not thought through your idea carefully. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. That is a big "if". You are not getting more noise, that noise is already there on SACD outputs. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. As the old Wendy's ad said: "parts is parts". Distortion is distortion, whether it is caused by the non-linearity of magnetic tape or by the non-linearity of semiconductors. That's interesting. So you are saying cross-over distortion is the same as clipping distortion? Or jitter distortion? The linearity curve of unbiased mngnet tape looks very much like the curve of an unbiased push-pull stage. Which part of "memory effect" do you have trouble understanding? |
#185
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:dfbb6$40369db0$c247604 I would have to verify this with actual measurements, You do that. Yes, I will and I will post the results, good or bad. but just from a theoritical point of view, noise would slightly reduce crossover distortion. It would move the signal to a more linear portion of the transfer curve. No, it would not. You are thinking of using sufficient DC bias so that only one side of the complementary outputs stays on, always. That is different than using noise. I see that you do not expect noise to reduce crossover distortion. It is very possible that you are right. The difference between you and me is, I have thought of something new, and I will try it to see if it works. You on the other hand, reject the idea because it is outside of your range of experience. The difference is that you have not thought through your idea carefully. It may be only a small improvment. Even if it caused only a *slight* reduction in crossover distortion, why get rid of it? Why, if it does not? All you getting is more noise. That is a big "if". You are not getting more noise, that noise is already there on SACD outputs. Bias moves the operating curve of tape, to a more linear portion of its' range. Hysteresis is a memory effect, and it's very different from cross over distortion. As the old Wendy's ad said: "parts is parts". Distortion is distortion, whether it is caused by the non-linearity of magnetic tape or by the non-linearity of semiconductors. That's interesting. So you are saying cross-over distortion is the same as clipping distortion? Or jitter distortion? The linearity curve of unbiased mngnet tape looks very much like the curve of an unbiased push-pull stage. Which part of "memory effect" do you have trouble understanding? |
#186
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:dd41e$40369df3$c247604 BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. It sounds like you are saying there are no op-amps with 120 db linearity. I would find that easy to believe. Maybe we should confine discussion to realistic distortion specificatations. Maybe you have trouble understanding what I said. For the 4th time, I am saying that it is not trivial to design active filters with -120dB THD+N. I did not say there are no op-amps with that kind of linearity, or that capacitors will be the problem. Think about the care you need to take to get all spurious noise contributions to be 120dB down. Think about the contribution of noise from all the passive parts (like resistors) as well as from the op-amps. Think about the bandwidth requirement for the op-amps to mainatin a good loop gain so that the filter works correctly, and that all distortion effects can be reduced. Think about the difficulty of making mwasurements at the -120dB level. As an example, say you have two 10K resistors in your active lowpass filter, and you have the classical Sallen-Key 2nd order configuration. That 20K will give you a noise voltage over a 20 KHz bandwidth of 2.5 uV, which is more than -120dB below 2VFS. So you can't have anything approaching 20K in series with the signal. I did not say that it is impossible to do. I said it is non-trivial, meaning it is not a trivial task. |
#187
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:dd41e$40369df3$c247604 BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. It sounds like you are saying there are no op-amps with 120 db linearity. I would find that easy to believe. Maybe we should confine discussion to realistic distortion specificatations. Maybe you have trouble understanding what I said. For the 4th time, I am saying that it is not trivial to design active filters with -120dB THD+N. I did not say there are no op-amps with that kind of linearity, or that capacitors will be the problem. Think about the care you need to take to get all spurious noise contributions to be 120dB down. Think about the contribution of noise from all the passive parts (like resistors) as well as from the op-amps. Think about the bandwidth requirement for the op-amps to mainatin a good loop gain so that the filter works correctly, and that all distortion effects can be reduced. Think about the difficulty of making mwasurements at the -120dB level. As an example, say you have two 10K resistors in your active lowpass filter, and you have the classical Sallen-Key 2nd order configuration. That 20K will give you a noise voltage over a 20 KHz bandwidth of 2.5 uV, which is more than -120dB below 2VFS. So you can't have anything approaching 20K in series with the signal. I did not say that it is impossible to do. I said it is non-trivial, meaning it is not a trivial task. |
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:dd41e$40369df3$c247604 BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. It sounds like you are saying there are no op-amps with 120 db linearity. I would find that easy to believe. Maybe we should confine discussion to realistic distortion specificatations. Maybe you have trouble understanding what I said. For the 4th time, I am saying that it is not trivial to design active filters with -120dB THD+N. I did not say there are no op-amps with that kind of linearity, or that capacitors will be the problem. Think about the care you need to take to get all spurious noise contributions to be 120dB down. Think about the contribution of noise from all the passive parts (like resistors) as well as from the op-amps. Think about the bandwidth requirement for the op-amps to mainatin a good loop gain so that the filter works correctly, and that all distortion effects can be reduced. Think about the difficulty of making mwasurements at the -120dB level. As an example, say you have two 10K resistors in your active lowpass filter, and you have the classical Sallen-Key 2nd order configuration. That 20K will give you a noise voltage over a 20 KHz bandwidth of 2.5 uV, which is more than -120dB below 2VFS. So you can't have anything approaching 20K in series with the signal. I did not say that it is impossible to do. I said it is non-trivial, meaning it is not a trivial task. |
#189
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DSD Recording Good. PCM recordings bad?
Robert Stanton wrote:
chung wrote in message news:dd41e$40369df3$c247604 BTW If you know of op-amps with 120 dB linearity, let us know what they are!! :-) Sounds like you answered your own question. It sounds like you are saying there are no op-amps with 120 db linearity. I would find that easy to believe. Maybe we should confine discussion to realistic distortion specificatations. Maybe you have trouble understanding what I said. For the 4th time, I am saying that it is not trivial to design active filters with -120dB THD+N. I did not say there are no op-amps with that kind of linearity, or that capacitors will be the problem. Think about the care you need to take to get all spurious noise contributions to be 120dB down. Think about the contribution of noise from all the passive parts (like resistors) as well as from the op-amps. Think about the bandwidth requirement for the op-amps to mainatin a good loop gain so that the filter works correctly, and that all distortion effects can be reduced. Think about the difficulty of making mwasurements at the -120dB level. As an example, say you have two 10K resistors in your active lowpass filter, and you have the classical Sallen-Key 2nd order configuration. That 20K will give you a noise voltage over a 20 KHz bandwidth of 2.5 uV, which is more than -120dB below 2VFS. So you can't have anything approaching 20K in series with the signal. I did not say that it is impossible to do. I said it is non-trivial, meaning it is not a trivial task. |
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