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I have to ask. Have you ever heard an amp that measures .0006% THD? I have yet to hear anyone tell me that kind of amp is their "favorite color" as you put it. I measured more amps as well. The amps that measured .01%+ THD sounded significantly better. Both were solid state amps. Both amps were placed in the same system of neutral toned electronics. My point is just because something measures good doesn't always mean it will sound good. This has been proven time and time again. I know what a dsp is and it's based on transistors, that is its limit. Dsps's don't just exist in computers and they are not only designed to process sound. They exist in receivers, car stereos, also calculators, and even microwaves. A dsp can try to emulate but it will never create true even order distortion unless it contains tubes. I know a lot of people say harmonics but that term is wrongfully used as they are two different things. Also remember there is not just one type of tube, but rather several and each tube has its own signature. Anyway If you wish to argue this further, please give me a link to a published white paper that states otherwise.
Again the transparency thing makes no sense. I don't know if it's the term "transparency" you're using or what. Can you provide a link so that I may read up on whatever it is you're talking about? I'm not sure why you provided reference to ENIAC of all things I find this a bit funny. Yes it contained tubes but no dsp of any kind was present. There were no transistors in ENIAC, which is one reason why it was so massive. I suggest you do some further reading on ENIAC in order to have a better understanding before you give reference of it. Also, regarding the whole digital signal thing. I have done some experiments regarding this. Me and a buddy of mine were curious one day so we decided to see if digital signals have any weakness. Our first experiment consisted of having two of the exact same digital setups.
Each setup consisted of a PS Audio Lambda transport connected directly to a Sony digital receiver via optical. There were no dacs involved. The only difference between the two setups was that one setup contained a PS Audio power re-generator. The only thing plugged into the power re-generator was the transport. It turns out there was an audible difference. The setup with the power re-generator sounded better. Why was this? Digital signals should not contain noise we thought. We then packed up our equipment and set out to his electronic lab where he works. We analyzed the digital signal and we then were able to confirm, the digital signal is only as clean as the power supply which produces it. It seems you have done some reading on the subject but very little if any experimentation. Anyway this thread has gone way off topic so this will be my last post. If you insist on having only equipment which measures good, then you're missing out on some really good music.
I can't say I've listened to an amp with distortion that low, but I can say depending on my mood, type of music, system synergy, etc that sometimes I would prefer something with ultra low noise and distortion, and sometimes I would prefer a thick syrupy tube. I did
not say that one single measurement is how we should judge a piece of audio equipment. I did say that measurements are useful because you will likely never have a chance to hear everything you would consider buying before you actually buy it. I did say that although it would be possible to objectively measure and rank audio equipment according to both preferences and absolute standards, no one has devised such a system, and no one likely ever will, because the audiophile market is so small. I also just realized that the fact that that many audiophiles are violently opposed to measurements of any kind will also be an impediment.
You are correct that transparency is is not a technical term. I would say it is more of a Platonic ideal and would define it as faithfulness to the original file. (We were talking about DACs here so I'm disregarding vinyl, and yes the tracks on your CDs,and SACDs are files.) It is reproducing the waveform exactly as it is stored in the file, without any coloration or alteration from the equipment used to reproduce it. Obviously, as you have stated before, this may not always be desirable for the
whole system. I am not advocating perfect transparency for the whole system however. Only for the DAC, which was the original topic of this thread. My reasoning is that since there are already enough variables in the audio chain, and even relatively cheap DACs can achieve near perfect transparency, that you should simplify things and remove the extra variable. Amps (especially tube amps) and your output transducers color the sound enough already, and EQ's and DSPs can replicate anything a DSP might add or subtract, and are easily changeable. It may not always be easy to replicate a specific sound, so I do not say it is wrong, or bad, to use such a 'colored' DAC, but because you can tweak free and cheap DSPs to your heart's content it is a better option for most people who have more time than money. In fact with a sufficiently advanced DSP, an ultra low distortion amp and phones could be desirable because a sufficiently advanced DSP could be tweaked to allow any type of sound, without the amp or 'phones interfering. Note that such a DSP probably doesn't even exist, but is theoretically possible.
Now on to ENIAC. I mention it because it is a digital computer based on vacuum tubes. A DSP is also a digital computer, but most today are based on transistors. Because they are both programmable digital computers they are capable of similar things. They manipulate data. Your digital music is data. If I felt like it could calculate even order tube distortion on a digital computer based on
wooden beads. I could do it by hand. One could make an
electrical or
mechanical analog computer to do it. Obviously these would not be in real time, but if you felt like punching the data back into a computer you could do it. DSPs do not generate effects by happenstance of their electrical properties, they do it by manipulating data.
As for your test, I'll assume you mean no
external DAC since that bitstream in a beam of light has to turn into an analog waveform somehow. Assuming you're
not fooling yourself about the audible difference, the only way you could notice a difference was if the
receiver was being powered by your line filter. Assuming that your Sony receiver has a substandard power supply and can therefore benefit from the cleaner power you may hear a difference. Note that this is the analog amplifier benefiting from the cleaner power. Not the DAC or the transport. To properly control this experiment you need to switch
only the transport between normal power and the line filter.
The reason I find your claim unlikely and assume your experiment is flawed, is because digital equipment does not, or cannot have noise for some magical reason, but because it absolutely rejects all noise below a certain threshold. A signal is either a one or a zero. On or off. High or low. Bright or dim. There is almost no in between. If the amplitude of the noise is not enough to turn a zero into a one then the noise is rejected. So even though you measured lower noise with the fancy line filer, it doesn't matter! If the sound is not
very obviously distorted, breaking up, dropping out, or just not there, then the noise is being completely rejected.
How would modern computers work otherwise? Your computer, from which you type your response is probably running from what is considered to be a low quality power supply with a processor running at least 10,000x audio frequency, and relies on every single bit being perfect so it doesn't crash. It deals with many clock generators running at many different frequencies all putting out their own RFI and trying to talk over each other, yet it still works. If digital signals were as susceptible to noise as you claim, then the average computer would hang 5 clocks after you pressed the power button.