mmerrill99

Ok, not able to contradict any of my points - just handwaving !

Fair enough, correct my misunderstanding!

Yes, I used the analogy of a long exposure photograph - the shutter being open for a number of seconds. The images that are stationery are reinforced on the photo & will appear sharp, clear & bright. Say the background light is continually adjusted during the duration of the picture - all we see in the final picture is the total accumulation of the various changes in background light into one background light level - we don't see the variations happening during the exposure time of the picture. This change in background light will be perceived in the real world when looking at the same scene over the same number of seconds. But if we are relying on the picture as proof of this we won' find any indication of this in the final picture. So this final picture is the equivalent of the FFT - it's showing an average So if this background light is actually an electric light & we are running a very heavy machinery which occasionally draws a lot of current & causes the light to dim - using this pic as our evidence we will not see this correlation between the machine's current draw & the dimming of the light. So all those who attest to having seen this intermittent dimming of the light will be told they are imagining it by those who wave the picture of the scene as 'proof' Now what about taking high speed snaps every 0.5 seconds & comparing the snaps for changes in the background lighting? Great, we are getting a step closer. But what if what's causing the machine to draw heavy current is because it has to stop & start very quickly & during our test we just keep it running at a constant speed? Well even with the pics every 0.5 secs we won't see any change in the backgound lighting. So we need the right inputs to the machine to cause the current draws which cause the lights to dim intermittently. So let's go back to FFTs - the background light is the analogy for the noise floor, it's intermittent dimming is the conjectured noise floor modulation & the input to the system needs to be a dynamic signal, not a fixed tone signal i.e run the machine with stop/starts (for example) not continuously at a constant speed. I conjecture that one possible approach to measuring this may be that we take many short FFTs done without averaging over a period of time when the system is processing the type of dynamic signals which is conjectured to result in noise modulation. But I suspect that there are many obstacles to actually achieving this otherwise it would have been done already

I'll not bother as this has been done so many times now that asking this is the circus which comes to town at regular intervals

I've always said that it was the hypothesis for what is going on & i was a bit more forceful about FFTs not being suitable for revealing such noise. That's not what I'm suggesting at all. Pkane made a claim that all he wanted to do was work towards how to measure this noise but all he ever did was argue that the noise was not a believable hypothesis (something I had already been through with him on another thread but yet he posts as if I had said nothing on that other thread & simply just repeated the same arguments as he had before) You miss the point of the cartoon - it's that measurements that are easy to make & well known are being used not because they are suitable for finding what we are looking for but because they are easy. You're getting the wrong end of the stick in that analogy. OK, the HDMI FFT doesn't show anything resembling noise modulation so why would you think it's suitable for revealing noise modulation - it's a simple as that? So you're question is meaningless - it's like asking the CERN people why a laser isn't going to reveal the existence of the Higgs Boson particle

It's up to you what you do but you made a claim that I was wrong & it was easy to measure the type of dynamic noise floor modulation that is conjectured to be in play in the ISo Regen

I will try to give you an answer seeing as no one else is even though you were told to ignore anything I post Unfortunately, this stuff is fairly technical & not easily understandable for the layperson. What Amir shows in the HDMI FFT tests has no bearing on the measurement of noise modulation. Well, again Amir talks about technical details & anybody who knows this stuff knows that what he does is post half-truths - the half that supports his viewpoint. He is not trying to find the technical truth as has been shown so many times in the past when he is questioned. So we are left with one of two conclusions - he either doesn't know what he's doing & doesn't realise the mistakes he is making (but he claims a CV full of technical nous) or he does know what he's doing & is following a particular world view or agenda? As to Pkane2001, my interactions with him here have led me to believe that he has a similar worldview & is not interested in technical truth. He ha 15 years experience with FFTs & says that noise modulation can easily be revealed by setting the correct parameters within FFT. Could I suggest that he shows an FFT of dynamic low level noise modulation that is correlated with signal? This would show that I am wrong & he could inform Amir of these settings & ask him to run his FFTs on the ISO Regen You ask why I don't do these measurements myself? It's because I'm not smart enough to know how to reveal this dynamically changing noise modulation that many conjecture is the underlying mechanism in play here. Many eminent audio designers & electrical engineers others are similarly flumoxed by how to measure this, John Swenson, John Westlake, Gordon Rankin, Bruno Putzeys, etc. So if there is something that all these have missed & it is as easy as Pkane & Amir are suggesting then let's see the details, FFTs & the proof that it is easy?

And you conclude from this....................?

Just to show Amir really doesn't know his stuff - I mentioned above the FFT he posted of a recording of a castanet & its MP3 version overlaid on it. Well here it is - the red is the original castanet recording & the yellow is the MP3 He posted this in some confused effort to show that pre-echo in MP3 is shown on this FFT (& the implied conclusion that his FFTs show any dynamic noise changes). So we are shown an FFT of a castanet - a high frequency transient & he says this about it " What is material is that at lower frequencies the two graphs do not at all look identical. The curves deviate as they should" So this transient has frequency elements below 100Hz & these are below -90dB & we are expected to believe that this is audible as the smearing of transients in pre-echo? He ignores MP3s compression method that removes elements of the sound which it deems psychoacoustically disposable. This FFT shows this compression as the changes in the frequency not just the change from pre-echos. What he is attempting to fool us (& maybe himself) with is that the changes we see in this FFT are solely down to the pre-echo introduced by MP3. He mentions that this pre-echo " the distortion is much more visible in time domain " but doesn't present the time domain FFT These basic errors are rife in his post & represent the type of technical misinformation he continually engages in. Based on his stated work role " For a decade I managed the signal processing group at Microsoft " this sort of misinformation, in what should be his area of expertise, is unforgivable & reeks either of great incompetence or huge disingenuousness.

Haha, I see Amir is trying to answer my points by proxy on his forum here Maybe I should answer by proxy - just this once? He states that in MP3 pre-echo distortion is "detecting fidelity of lossy compression, we do not use measurements." I wonder why when a measurement of such can unequivocally show such issues (although he doesn't show any measurements of this) - his FFT is showing all the frequency differences between WAV & 64Kbit MP3 - it doesn't show anything about pre-echo He follows in another post with more misinformation about DAC glitches, not knowing what they are or even reading the link I gave in the post of mine he quoted. It's amusing really Such is the lack of knowledge, level of misinformation & rush to judgement that passes on Audio SCIENCE review

Just to explain multitone test signals a bit. We are all probably familiar with two tone tests - it shows the IMD - intermodulation distortion products - in other words an ideal DAC would only have the two tones on the analog output but all dacs show other spurious signals along with the two tones. Multi-tone test signal goes further & uses maybe 30 tones or more arranged so that the IMD products fall between the test tone spikes & aren't masked by the test tones themselves. A source of multi-tone measurements of DACs that I posted before is here So here's an example of a 10 tone measurement on a Hifiman What you see in this plot is a lot of lower level signal (inter tone products) created between the tone spikes - beginning to form a 'grass' Now if this was a music signal what would happen is that there would be many more signal tones & many more inter tone products between the main frequency spikes forming a much more dense 'grass'. As the music signal dynamically changed this grass would fluctuate in accordance with the varying signal - don;t know what's so difficult to understand about this? You will find many more such multitone FFTs of DACs here (it's in russian but translate is fine) For instance two more plots to show that the 'grass' is different between DACs Makes interesting reading but don't know how well it correlates to audibility? The full set of DAC test measurements (including 30 mutitone tests at various signal levels) for many DACs & more is here http://reference-audio-analyzer.pro/en/report.php Noise modulation, anybody?

It shows me your intent & whether you are disinegenuously claiming "so let's come up with a better way to detect this noise." or whether this is just a ploy & what you are really doing is objecting to everything without any logic, just lots of handwaving You already stated that " What I do know, is that it's not hard to run an FFT analysis of a WAV file captured from the output of a DAC. With a hi-res ADC and proper settings, it should be easy enough to detect noise spikes in the output of such an FFT, even if they change in frequency. " So, either you think Amir doesn't know how to use his Audio Precision signal analyzer properly & his FFT is flawed or you believe his FFT shows all there is & the iso regen does nothing other than 5V cleansing? I believe that no matter what is said you will object because you believe that this FFT is correct & you are trying to argue for this while pretending to "come up with a better way to detect this noise" Not interested in your games when you are being duplicitous - genuine inquisitiveness & an open-minded approach to "detect this noise" I would be interested in discussing but you show no inclination towards this

Sorry, I should have said - other than the 5V clean up, do you believe Amir's FFT 'proves' that the iso regen does nothing.

Yes, but it's argued that any DAC which uses the 5V USB supply for power & doesn't sufficiently clean & filter it is badly designed - I would agree with this. But in his first FFT which showed no such improvement - what I'm asking Paul is doe sit "prove" the iso regen does nothing?

I'm asking you for the third time if you think Amir's FFT shows that the iso Regen does nothing? Your avoidance in answering this simple question is telling