Objective Reviews & Commentary - An Engineer's Perspective

October 1, 2011

Music vs Sine Waves

sine wave by Leon WilsonMEASUREMENTS & AUDIOPHILES: One of the goals behind this blog is to explore some of the more popular audiophile beliefs. Which ones are true, partly true, or completely false? When it comes to measuring audio gear there are many different beliefs but I often run into variations of these three (photo: Leon Wilson):

  • Measurements use test signals, not music, so they’re of limited use
  • Measurements fail to account for real world usage and loads
  • Measurements matter little as you can only trust your ears.

music snippits by inha leex haleMUSIC vs TEST SIGNALS: Intuitively music is far more complex than test signals. So it’s not surprising many believe such measurements cannot accurately convey the performance of audio gear. But there’s lots of well documented research demonstrating the right measurements using test signals can help predict the sound quality of a lot of audio gear. Some things to consider (photo: Inha Leex Hale):

  • Sine Waves - Sine waves are not some abstract signal created in a lab. They’re the primary building block of all sounds we hear. Analogies would be a single color of light or a pure chemical element from the periodic table. All the colors we perceive are combinations of individual wavelengths of light. And everything we experience in the physical world is made up of elements from the periodic table. And, in much the same way, music is just a collection of sine waves. A perfect sine wave is a single pure tone and has no distortion of its own. It's the most pure component of sound.
  • steinway by Mrs logicSteinways & Yamahas - The note "A" above "Middle C" on a piano strongly resembles a 440 hz sine wave. It's a relatively pure tone at a single frequency. The wood structure, nature of the strings, hammers, etc. all slightly alter that 440 hz sine wave. A Stieinway grand might have a slightly faster attack, a longer decay and a different set of distortion products than a Yamaha grand. These subtle properties are well enough understood it’s possible to simulate the sound of different pianos using software (photo: Mrs Logic).
  • Amplifier Distortion – Just as the sound of a particular grand piano can be simulated by understanding its distortion, the same can be done with amplifiers. In the mid 80’s Bob Carver challenged high-end audio magazines and ended up duplicating the sound of a seriously expensive Conrad Johnson tube amp using one of his inexpensive mainstream solid state amps. He did this by simply measuring the tube amp using test signals. The golden-eared editors had a very difficult time telling which amplifier was which despite the massive price difference. There are many other examples that demonstrate the power of proper measurements. If Bob Carver can “describe” and essentially equal the sound of a high-end audiophile amp using measurements that says a lot.
  • test track by Cushing Memorial LibraryYACA (Yet Another Car Analogy) – Much as music is more complex than test signals, public roads are more complex than a closed circuit on a racetrack. But when someone wants to figure out if Car A outperforms Car B they take them to a track where they can be evaluated under identical controlled conditions. There are too many uncontrolled variables in real world driving such as other traffic. Few dispute a racetrack is the best overall way to evaluate acceleration, braking and handling limits of cars. A test bench for audio gear offers the same for audio gear. A fair and valid performance comparison is only possible under rigidly controlled conditions—not casual listening or driving.
  • Correlation – Lots of studies compare measurements made with sine waves to perceived distortion when listening to music. And, for decades, the research has supported a strong correlation between the measurements and what we hear. It’s not black and white when you’re dealing with human perceptions, but virtually all of the research has pointed towards various measurement thresholds that help define what people can perceive under various conditions.
  • Sufficiently Transparent – When there are audible differences between audio gear it’s sometimes difficult to definitively pick a clear winner as that’s subjective and personal preferences will bias the result. This is especially true with things like headphones, speakers, and phono cartridges. But with electronics like amplifiers, DACs, pre-amps, etc. measurements can help a lot. It’s been shown once all the right measurement thresholds are met, the equipment in question becomes essentially “transparent” in the signal chain—i.e. it doesn’t alter the audio signal in an audible way. For example, Meyer & Moran demonstrated you can insert an A/D and D/A operating at 16 bits and 44 Khz into a high resolution SACD signal path and even skilled listeners could not tell when the extra hardware was present. The A/D and D/A were sufficiently transparent and did not alter the sound enough for anyone to detect.
  • Myth Busted – Sine waves are not some artificial signal with no basis in reality. They’re  a well proven method to reveal distortion in audio gear and they’re a building block of all sound we hear including music. And audio engineers have more tricks up their sleeves than just sine waves.

hd650 vs ah-d2000REAL WORLD USAGE & LOADS: Some claim measurements fail to account for real world conditions. But that’s all in how the tests are done. Some tests account for a much wider variety of conditions than typical listening tests:

  • Test Loads – Proper tests are done using proper loads. And it’s not uncommon to run at least some tests with reactive loads or even real loads. It’s not difficult to model a loudspeaker or headphone driver on a test bench. And it’s easy to compare the results with various kinds of loads including real ones. Hence there’s a pretty good understanding and body of evidence as to how simulated loads affect the performance of audio sources.
  • Complex Test Signals – Not all tests are just a simple sine wave. Some involve sweeps or other techniques covering the entire audio spectrum, using multiple tones, impulse signals, chirps, pink noise, square waves, etc. And measuring noise doesn’t require any test signal.
  • Worst Case Testing – It’s not that difficult to come up with worst case operating conditions that represent real world usage. I did just that in developing the criteria for the O2 headphone amp. Once you establish the worst case criteria, tests can be run to verify the performance under those conditions. If the gear measures well enough to be transparent even under worst case test conditions, it’s a safe bet it will also be transparent under realistic conditions in the real world.
  • Audio Differencing – It’s possible to test many kinds of audio electronics using a method known as analog or digital audio differencing. These tests can be done using real music and real loads (i.e. headphones). In essence, the input and output are matched in level and subtracted from each other. This method was originally put forward by Baxandall and Hafler as a method for evaluating power amplifiers under real world conditions. Differencing captures nearly all forms of distortion and can be quantified objectively by measuring its level and spectral properties. It can also be quantified subjectively by listening to the nature of the difference signal and how unpleasant it is.
  • Myth Busted – If anything it’s more common to fully challenge audio gear on a test bench than in listening tests. Just like testing a car on a track, it’s generally best to find the ultimate limits on a test bench rather than in real world usage.

ear by travis isaacsTRUSTING YOUR EARS: Audiophiles put a lot of trust in their ears and subjective impressions certainly matter. But there's a problem. Human senses, including hearing, are greatly influenced by other factors (photo: Travis Isaacs).

  • Primal Brain - A primal and involuntary part of our brain constantly filters our senses to avoid sensory overload. For example, your brain automatically filters out other conversations at a noisy party so you can better hear the person you’re talking to. Check out how the brain involuntarily filters what you hear with this brief BBC video demonstrating the fascinating McGurk Effect
  • Seeing & Hearing – In the video above, if you close your eyes your hearing is accurate but with your eyes open, your brain deceives you. It turns out when listening to audio gear you have go one step further and remove the knowledge of what gear you’re listening to. Otherwise much the same thing happens—the brain tries to help out and serves up an altered version of what you’re listening to. The objective geeks call this “sighted listening bias” and it’s been well proven in many studies.
  • Bed Sheets & Hearing – The simple act of throwing a bed sheet over an equipment rack can make allegedly obvious differences in sound quality disappear. The listener’s abilities, room, music, and the hardware remain unchanged, yet just removing the knowledge of which equipment is playing removes the previously audible differences. This has been proven again and again, even in the homes of audiophiles, by listening tests such as this one: Matrix Audio Test
  • Conditions Are Different – Just because a headphone amp sounds good with 300 ohm Sennheisers doesn’t mean it will sound equally as good with 25 ohm Denon headphones. And gear that might sound great with classical music may fall on its face with the next guy’s hip hop. So listening tests are often only valid for a particular set of audio preferences, conditions, type of music, volume, etc. And all those things differ widely from one person to the next. I’m not saying these tests are useless, but they’re highly subjective and very difficult to compare between people and conditions.
  • Ears Are Different – If Michael Fremer at Stereophile listens to a piece of gear and declares it best-in-class what does that really mean? It’s much like a wine critic saying the same thing about a particular wine. But the next wine critic will often choose a different wine as he had different tastes. The same is true in audio and it’s a fundamental problem with subjective listening. Everyone’s tastes, preferences, priorities, hearing acuity, listening skills, etc. are different. One man’s “detailed” is another man’s “excessively bright”. So it’s difficult to trust someone else’s ears. And, there are not many stores where you can walk in and audition high-end headphones to hear them with your own ears before purchasing. Measurements greatly supplement these subjective reviews and provide a much better means of comparison.
  • No Contest – With other controversial topics, say global warming, there’s typically conflicting research. But, in this case, there’s lots of research supporting the problems with sighted listening and essentially nothing credible opposing any of it. If there’s some problem with blind listening tests, why hasn’t the well funded high-end audio industry managed a single study supporting the supposed advantages of their products and/or sighted listening?
  • Myth Busted – The points above explain why it’s difficult to trust your own ears and trusting someone else’s ears is much like trusting a wine critic. Hence the classic “you can only trust your ears” belief is highly suspect. Objective measurements, however, generally can be trusted as they’re immune to all the issues above.

OTHER RESOURCES: If you’re still not convinced the three popular beliefs are more myth than reality, or if you want more information, the following links are worth a look:

  • Audio Myths Workshop Video – This is a fascinating video covering everything from human psychology to assorted listening trials. One of the presenters is Ethan Winer who has also made available audio files to allow your own comparisons.
  • Science and Subjectivism in Audio – Douglas Self shares his views on this debate in an older but still poignant article. He’s the engineer behind some high-end gear such as the current flagship Cambridge Audio products. He’s published some of the most highly regarded books on audio design in the world.
  • Subjective vs Objective Debate – This is my own article covering more of the philosophical differences between the “trust your ears” and “measurements are best” camps. The comments are also enlightening.
  • Testing Methods – I share some of my thoughts on how I test audio gear and why. Tests should be done in standard ways to allow fair comparisons between gear and they should be verifiable by others.

BOTTOM LINE: If you want to know the ultimate performance limits of a car you take it to a test track or race course. And if you want to know the ultimate performance of audio gear, you put it on a test bench and use an audio analyzer to make appropriate measurements. Subjective impressions are still important in both cases. For example, the numbers tell you nothing about how easy the controls are to use. But when it comes to determining if the BMW or Mercedes is the higher performance car, measurements offer the best answer. The same is true when comparing audio gear.


  1. Fantastic. Thank you: you have summerized perfectly a dozen of links that I am tired of posting in FB groups and even in my own blog ! Congratulations, sir. Let's see (and even listen) if, little by little, we can remove that veil that covers Hi-Technology applied to sound reproduction from Hi-Priced products.

  2. Your post showed up in my rss feed while I was reading this: http://news.cnet.com/8301-13645_3-20113895-47/can-sound-quality-be-measured/
    That was an interesting coincidence.

  3. Actually, the global warming discussion shows some parallels to the blind testing discussion - work disputing the validity of either commonly involves cash flow from those with an interest in keeping the status quo.

    Maybe those speeding neutrinos measured lately would make a better example, or the still-unproven string theory... Or how to build the perfect loudspeaker...

  4. Dear NwAvGuy, very good post as always, but you did a big error: Syntogy Ivory piano is based on sampling, not on DSP. In fact it takes 50Gb of disk space to install.

    The most advanced pure sample-free piano is Pianoteq, as while it is very good, as of today sample based ones have a small edge over it.

  5. Thanks for all the feedback. And good point Ernesto. I'll fix the link but the concept is the same.

  6. Just a quick comment on why DSP is needed in Piano software.

    First, the sound has to be processed for simulating a room if you are going to use the piano with headphones. With good placed monitors this is not necessary.

    Second, pianos feature an effect called "sympathetic resonance", meaning that some strings can make others vibrate (if you have some key pressed) Reproducing this effect with sampling is not feasible (full sample would be like 88 factorial, a more reasonable one like (88 10 k) So they try to model it, with some success IMHO.

    In fact, I'd guess a modelled piano will be indistinguishable from a real one in a few decades. For bass and treble notes modelling works very well, but the middle range always sound "synthetic". Is that an effect of the human ear accuracy a those levels?

  7. Any wave is made up of a series of sinusoidal waves.

    So if a device cannot do a single sine wave properly, it wouldn't do better at reproducing, say, 17 sine waves at different frequencies simultaneously.

  8. I once bought a pair of second-hand speakers, they seemed to be okay when I tested it on the spot with music. Brought it back home, felt something wrong with it after a few hours of listening. Played some sine tones, one of the tweeters was audibly distorting.

    Seller refused to take it back, claiming "I tested it and they were okay", and "he used it for a long time and heard nothing wrong".

    Went to a shop that sells the parts, bought a NOS (I hope it was new) replacement, much worse.

    Had to demonstrate to the boss with a sine tone and the less-spoiled tweeter to compare against.

  9. Within the scientific community there is almost no debate that climate change is both real and anthropogenic. Big word there. I R SMRT. :P

    I learn something with every article. :)

  10. @ernesto @nwavguy Actually, Nwavguy's post is technically quite correct. The system uses samples as base waveforms, instead of pure generation of base waveforms. DSP is still used to "flavor" the result based on the input(s) of the player. This confusion that somehow sample-based DSP instruments are grossly different other than the waveform source seems to be widespread in the musician community.

    Nice article, as usual.


  11. "Maybe those speeding neutrinos measured lately would make a better example"

    At least the neutrino's ability to exceed the speed of light was theorized prior to the experiment.

    There's another thing measurements give us... which is the ability to define an objective framework which allows more accurate subjective evaluations of gear. For example, I can look at the differences between a Corvette GS-1 and BMW M3 (about the same price point) on a test track and then use that to evaluate the "gear" subjectively when I'm test driving the cars. Then my subjective impressions are "more" valid than they would be without the objective framework the track results provided.

    In audio, however, there is no standard Nurburing-style test track/conditions and therefore one's subjective evaluations are less valid because they have nothing objective that they are based on.

  12. Bleh, just read an article on a reputable tech site insisting that music is more complex than sine waves therefore all measurements are broken...

    Some people never learn.

  13. Thanks for all the comments. The Piano DSP comment was just an example. The biggest issue with reproducing a grand piano in software is the final part of the chain--the speakers (or headphones). That's why it will never sound the same and some might consider it "artificial".

    The Carver example is much more applicable as both use the same speakers. So it's a much more level playing field for comparison than comparing a real piano to a reproduction.

    Global warming is just an analogy. At least the few on the other side have commissioned some studies. In high-end audio I'm not even aware of that happening.

    @Willakan, what's the "reputable tech site"? Please contact me privately if you care to share it?

  14. Maybe he is talking about this?


    Quite amusing IMO.

    CNET in general is full of crap. . .

  15. Hi guys, I'm sorry I wasn't clear, I'll try to explain a little bit more in depth.

    Sample-based software pianos are used in recording and are completely indistinguishable from a real piano on a recording. No DSP is needed at all in the majority of the cases (look at VSL Vienna Imperial) but given the complex resonances that playing without dampers cause, some software use it. Some player want to use reverb, etc... that's another legitimate use.

    If you want to play for instance Für Elise, no DSP is used. *The sampled waveform is what you get" and no algorithm as of today can reproduce it from some "base" waveform in a satisfactory way. Sample based pianos use DSP to add some effect like reverb, etc... but the basic timbral characteristic is unaltered. So IMVHO opinion the example is not the best. If you play a single note or a chord in Ivory II, no DSP is used, and BTW I own the software.

    The pianos which sound artificial in the middle range are the modeled pianos, that is to say, software which is not based on samples.

  16. Most of what I just read was accurate, or maybe all of it was accurate. I read and sometimes respond to issues of headphone sound, and most of those involve hundreds of posts declaring how the item sounds with different music and equipment, but those are generally all absolutes, with little or no references to go on. So I have taken up the task of comparing headphones to each other, sometimes applying simple EQ settings to see if I can compensate for negative differences, usually in the cheaper item. I can't necessarily eliminate all other factors such as amping differences, but mostly those are very small compared to headphone differences, headphones being what they are.

  17. The fact that no pianist can identify a sampled piano note from a real one in a recording, indeed supports quite well NwAvGuy's argumentation.

  18. Thanks everyone for all the piano comments. To hopefully get back on topic, I've removed the link to the piano software from the article. This article is about measuring distortion in audio electronics such as headphone amplifiers.

  19. I was indeed talking about the CNET article, from the blog of their part time audiophile writer. It reels out the usual load of myths - which basically can be shortened to "Audio is, like, complex so it breaks science."

    Apparently people get paid to write this crap.

  20. Well, headphones and speakers are complex. Complex loads, that is, but I think people figured out a lot of stuff about those, a long time ago.

    Also I would hesitate to call most any tech site, especially CNET, as "reputable."

    As for on-topic discussion, any thoughts on why THD (or THD+N, for a single tone) seems to be quoted a lot more than IMD? It seems like the latter is a more useful and stressful metric. (Not to mention, THD products and noise can also be measured in an IMD test.) With multiple frequencies, there's more of a question of which frequencies to use together, but from my view as a casual observer, CCIF and SMPTE seem established enough already.

  21. For Sound System Design (talking large PA's here) we use SIMM measurement with flat frequency mics.... Why can't this be used for hi-fi equipment, thus eliminating the "test tones are too simple" argument?

  22. @Mikeaj, I suspect there are multiple reasons why you see THD quoted (and used) more often. Without using software analysis it's much harder to measure IMD. So, historically, THD used to be much more practical. Another reason are sweeps. While you could do sweeps with two tones spaced close together, they're less practical for widely spaced tones such as SMPTE. And, typically, THD at 1 Khz will yield a lower, and more impressive, number than IMD. So that gives manufactures another reason to quote only THD.

    Matias, I'm not sure what "SIMM" is? Do you mean something like MLSSA or Praxis? The techniques that deal with room acoustics are notably different than measuring something like an amplifier. Similar techniques can be used such as the impulse, multi-tone and chirp signals mentioned in the article. An example would be: Prism dScope Multi Tone Tests

  23. I meant to type "SIM" which is Source Independent Measurement. The idea is you play a reference track through the device in question, SIM tools compare the output of the device to the reference and measure the differences. For big PA tuning we just use a flat-response microphone and compare it to the input signal of the PA, obviously this is not super precise, but I imagine with the right equipment you could get something that is precise enough (though admittedly, I am not an EE guy).

  24. @Matias, I think that's a trade name from Meyer for their FFT system that compares two signals--in your example the one feeding the speakers and the signal from the mic. And, I suspect it still uses test signals not music? If it can perform analysis using music then it's using a form of audio differencing as I discussed in the article. But, AFAIK, it's mainly optimized for live sound use (i.e. tuning for acoustics, speaker placement, etc.).

    An audio analyzer, like a dScope or Audio Precision, can do much the same thing with its own digitally generated signals. They're optimized for testing electronics rather than speakers (although both have speaker/acoustics measurement abilities).

  25. Yes, it is a trade name, but most everyone calls the idea SIM regardless of whether or not it's a Meyer product (for instance we use SMAART, which is a Rational Acoustics product). The big thing with this is the test doesn't really require any type of signal, playing tones over big PA is a great way to drive everyone crazy, so most of the time it's music that's played over it. Since test signals are a good way to measure the way electronic's performance, shouldn't playing music instead of the test signals also measure performance? Again, apologies if I'm over-simplifying things. If you have precise enough equipment to measure the difference between the output of a device and a reference signal (in this case music), you should still see the same results as using test signals, right?

  26. I did some more reading on the Meyer SIM3. It can't measure things like distortion with any precision without using its own internally generated test signals. And even then it still lacks the resolution of an audio analyzer like the dScope or an AP. When using independent sources (like music) it's measurement resolution is fairly coarse. Meyer calls the validity of such measurements "coherence" and talks about all the factors that degrade the accuracy. While less than 100% coherence is fine for acoustics and speakers, it's not going to reveal the subtle differences between say two well designed headphone amps.

    Audio differencing is extremely revealing of any distortion or non-linearities by a piece of equipment using test signals or real music. The problem is quantifying the result into meaningful measurements like THD, IMD, phase error, various kinds of noise, and an accurate transfer function. It seems even the Meyer SIM3 is unable to do that reasonably accurately without using specialized test signals.

  27. There are measurements that correlate to music reproduction quality, but are not often performed and rarely published. These include amp crossover distortion, frequency response with 1/12th octave or better resolution over 4 PI steradians, spectral decay, inter-modulation distortion at full signal level (Doppler distortion), spectral contamination, and phase response.

    The latter is controversial because 99+% of the population is phase deaf from listening to reproduction systems that mangle phase. This is a vicious circle.

    I ask if the reproduction systems sounds fine to you, is it because you only compare it to other reproduction systems using flawed recordings, or do you listen to natural acoustic music often enough to maintain a perceptual standard?

  28. @Acuvox, I have tested for all of those things at various times and you will find most of them in my O2 Amp Measurements.

    The "skilled listener" and "source material" arguments are interesting. I try to approach both in a real-world way.

    I agree there's a significant range in listener abilities. Interestingly, studies have shown musicians--even classical musicians--make poor critics of audio gear despite the fact they know what the real instruments are supposed to sound like. The most often cited reason is they tend to focus on the performance itself rather than the reproduction details. That's just how their brains are usually "wired". Conversely, recording engineers typically score much higher in discerning subtle differences in audio gear. It's part of their job to hear flaws in recordings rather than performances.

    I think it's most realistic to use a broad cross section and a large sample group when conducting listening tests. Meyer & Moran, for example, used a large group including audiophiles, recording engineers, and students. Despite the large group, none of them could discern the down-sampling and extra A/D and D/A hardware in the signal path under normal listening conditions over 500+ trials. Not one. It's hard to claim every single person in those 500+ trials lacked the right skills or hearing ability.

    I believe people should evaluate gear using recordings representative of what they typically listen to. If it takes an extremely rare audiophile recording to reveal differences in audio gear, how relevant are those differences in real-world use?

  29. NwAVGuy,

    This article should be a sticky in EVERY audio forum known to humanity.

    A great man once said, (not a quote, but to paraphase) that people need to understand that something might be good for them, but NOT for me. IOW, you may be right ... for you ... but NOT for ME.

    "Audiophiles" like to impose their "perception" of the world on other people because they "trust their ears". Nevermind that their hearing could be impair (just due to age). Nevermind that they are listening to different music then you are. Nevermind that YOUR ears say otherwise. Their ears cannot possibly be wrong, and by their (mistaken) corrollary, your ears MUST be wrong.

    Some things are absolute, like black is darker than white. Or blood is thicker than water. But other things are NOT absolute and colored by perception. For example, I like purple. No one can argue that purple is any better or worse than any other color. I may like purple, you may not.

    Again what's right for me, may not be right for you.

    Transparency of music is something that was argued about from the infancy of mp3 music players and ipods. I remember people posting on Hydrogenaudio that 128 AAC was transparent, the ipod had the best sound quality in the galaxy, and the ipod earphones were better than most headphones (because the SQ of ipods sucked back then [but Apple never posted SNR, so it was hard to disprove] and 128 AAC was NOT transparent). Now, no one will support those arguments, but they were views held by a large portion of the Hydrogenaudio community at the time IIRC.

    Today, if you post that you can hear the weaknesses in the psycho-acoustical model of VBR, so XXX VBR MP3 or AAC is NOT transparent to your ears, some A-hole will put on their Hydrogenaudio hat and call you a liar. They will say "have you ABX tested blah blah blah". Of course you have, or why would you have posted that you can hear the difference??? If I transcoded two different version of the same file and I can perceive how and where it is different, then I don't need to do anymore testing. It's NOT transparent for me ... for my ears.

    Ultimately, no one has the right to tell you that you are not hearing what your ears are telling you, because their ears are telling you that you are wrong. Or because it's been "proven" on Hydrogenaudio.

    Stephen Hawking once said time travel was impossible, but recently changed his mind. Physicists once believed that nothing could travel faster than the speed of light. Now CERN has reported that they have measured particles traveling faster than the speed of light.

    Everything changes ... except "audiophile's" fixed set of dogma. Dogma that is based on SUBJECTIVE experience (ABX testing at sites like Hydrogenaudio). NOT science, but BELIEF WORSHIPPED AS SCIENCE.

    If (as posted on Wikipedia) the most people over 25 cannot hear the mosquito ring tone, because they have lost the ability to hear 17.4 khz ... then most of Hydrogenaudio is can NOT hear above 17.4 khz and their ABX testing for transparency is fatally flawed and outright WRONG for people who CAN hear 17.4 khz.

    "Audiophiles" need to learn to stop imposing their dogma on others. As you posted, their are many ways that our ears can deceive us. And your ears are NOT my ears, so our experiences can be very different. Listening to music is very subjective. What is transparent to you might be less than transparent to me. Respect my views and don't try to impose your dogma on me.

    It all comes down to respect of another human being. Yet there is always those who like to belittle others and call them a liar, because their beliefs/experience don't match that persons's dogma/"trusting their ears" BS.

  30. @Anon, thanks for your comments. I would add it's useful to establish reasonable levels of transparency for "the masses". While one can always argue there may very rare listeners who are an the exception, sufficiently large studies go a long way towards defining what matters to the other 99.9%. When studies like Meyer & Moran involve 500+ trials and dozens of people, including fresh eared college students, it's hard to dismiss them on the "their ears are not my ears" principal.

    Blind listening of any sort is really rare--too rare--because it often doesn't reveal the desired outcome. So it's marginalized and shunned--especially by those who have spent a lot of money on this hobby or those with a commercial interest. And those people are often the most influential.

  31. Some time ago we have done some blind listening to couple of power amplifiers and noted the differences. Later, when we compared measurements they correlated pretty much with our blind listening results. The most influential factors where- intermodulation distortions, continuous power capability and dampening factor. The amplifier with brighter frequency response but higher imd sounded worse then other amplifier with smaller bandwidth but smaller imd. In my experience, any amplifier with imd less than 0.1% sounded quite good.

  32. Its a real leap of faith to say an amplifier than can reproduce a handful of sine waves with inaudible distortion will perform just as well with real music which when modeled aprroaches an infite number of sine waves.

    No one knows what an amplifiers noise floor is when playing music, it can't be measured. In other words that "noise" or IMD+N as EE's term it when there are too many sinewaves played to be analyzed is what makes amplifiers sound different.

    The EE's solution is to color or mask the signal with heavy amounts of negative feedback.

    Since no one knows how the perception of hearing handles things like distrtion, we don't know if a simple linear amplification device is better or worse than a high distortion device (as in the O2 where the distortion is 'cancelled out' with NFB) is more accurate to the sense of hearing.

    In simple terms should we be adding huge amounts of NFB to the signal to cover-up a terrible performing open loop gain performance? Or should we start with the most distortion-free device available and let out hearing do its own cancelling?

    Please show us the DBT (statistics) on that question. Hint: there are too many variables to economically develop a null hypothesis.

  33. @Anon, if you read the article carefully you will learn it's possible to figure out the noise floor, and distortion, while playing real music contrary to what you suggest. It's called audio
    differencing and it's been done quite a bit--it's just that subjectivists, and high-end gear makers, like to ignore it. Baxandall, Hafler, Waslo, and others, have published very credible papers on the topic. See the Doug Self Subjective link in the right hand column of this blog for some added info and there's much more at http://AES.ORG.

    It's possible to subtract the input of an amplifier from the output. What you're left with is everything added by the amplifier. This has been done at least 3 different ways: Passively, actively, and in the digital domain (i.e. Audio DiffMaker). With an amp that measures well on sine waves as I've outlined, it's hard to even hear the difference signal by itself let alone underneath the music. The absolute level of the difference signal is consistent with the THD+N sine wave measurements (i.e. -80 dB, etc.).

    You're just mostly recycling the usual classic audiophile myths--such as NFB being a bad thing--without providing any objective evidence to support your claims. I've linked to several resources in my articles, especially the Subjective vs Objective article, with respect to DBT (blind) studies. There are dozens of peer reviewed blind studies published by the Audio Engineering Society and even papers on the topic itself.

    The bottom line is very simple. When you take someone like yourself who insists there are obvious audible differences between amplifiers that measure sufficiently well, and throw a bedsheet over their own electronics in their own homes, and ask them to identify their own amp, or a much cheaper one with decent specs, they fail. Every time. If the differences are so obvious, why do they disappear by just removing the knowledge of which amp you're listening to?

    There are dozens of peer reviewed studies that support the general arguments made in this article. To my knowledge, there are none supporting the argument readily audible differences exist between audio electronics that measure sufficiently well. If such differences were so readily apparent, and important, wouldn't at least one high-end manufacture have published at least one DBT demonstrating the advantages of their products by now?

    See also: Headphone Amp Measurements at InnerFidelity

  34. I've just today added a Behringer UCA222 to my lovely JDS Labs O2, and it's actually lowered the already low noise (audible hiss) vs. using the analog Line-Out jack from my MacPro tower. Not bad for $30 bucks! Mind you, I was already getting basically zero hiss at normal listening levels, but it's nice to have removed the computer's amp from the equation.

    Now OSX still uses the system volume control to adjust the volume of the line-out from the Behringer. I'm trying to determine if there's any reason to leave the Behringer RCA output at less than 100% (assuming it's meant to run at full-volume without clipping) or if I should turn it down to 2/3 volume like I was doing with the Mac's headphone out?


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