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#1
Posted to rec.audio.high-end
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LP inferior?
"Eeyore" wrote in message
... Bill Noble wrote: if you are sampling a sine wave (or square wave) at a single frequency, so long as your sample rate is 2X or greater than the fundamental, you will not get ALIASING of the fundamental. This says nothing about distortion of phase or waveform. If phase information is important, a significantly higher sampling rate is needed - 10X is much more typical. A control system for a large airplane, for example, had a roll off at 4 Hz - we found it necessary to sample the input data at 60 hz to prevent phase induced instability. That's 15X the maximum passband frequency. I see no reason why this kind of effect does not apply at audio frequencies as well. Because the ear is insensitive to phase info at the relevant frequencies. Graham not clear what "relevant" means in this context, but I have run tests (decades ago), to duplicate what was widely documented, as follows: pair of headphones, single white noise source - add phase shifting network to one side only - white noise is indistinguishable via spectrum analyzer before/after (or left/right). Put on headphones. hear a tone equal to the pass band of the phase shifting network. as I recall, I did this in the 1Khz range, but I honestly don't remember. My point here is that there is significant relative phase detection capability in the pair of human ears that not commonly understood. My duplication of these experiments strongly suggests that your statement about insensitive to phase is incorrect. |
#2
Posted to rec.audio.high-end
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LP inferior?
On Nov 25, 11:02*am, "Bill Noble" wrote:
"Eeyore" wrote in message ... Bill Noble wrote: if you are sampling a sine wave (or square wave) at a single frequency, so long as your sample rate is 2X or greater than the fundamental, you will not get ALIASING of the fundamental. *This says nothing about distortion of phase or waveform. If phase information is important, a significantly higher sampling rate is needed - 10X is much more typical. *A control system for a large airplane, for example, had a roll off at 4 Hz - we found it necessary to sample the input data at 60 hz to prevent phase induced instability. That's 15X the maximum passband frequency. I see no reason why this kind of effect does not apply at audio frequencies as well. Because the ear is insensitive to phase info at the relevant frequencies. Graham not clear what "relevant" means in this context, but I have run tests (decades ago), to duplicate what was widely documented, as follows: pair of headphones, single white noise source - add phase shifting network to one side only - white noise is indistinguishable via spectrum analyzer before/after (or left/right). *Put on *headphones. *hear a tone equal to the pass band of the phase shifting network. as I recall, I did this in the 1Khz range, but I honestly don't remember. My point here is that there is significant relative phase detection capability in the pair of human ears that not commonly understood. My duplication of these experiments strongly suggests that your statement about insensitive to phase is incorrect.- Hide quoted text - - Show quoted text - I've always found it difficult to accept this notion, based on several observations as an audiophile for 50 years. Mind you, these are "speculations" but I would love to see somebody set out to verify them: 1) Extreme frequency responses. I've always felt that amps with wideband response at the low end sound more powerful and have better defined bass than their rolled-off counterparts (i'm talking below 20hz here). And likewise, I've always found amps with wideband high end to sound more realistic on triangles, cymbal after-ringing, etc. Conventional theory says one just doesn't hear these things. I've seemed to, although I will grant you it could just be a placebo effect. 2) "Rounded" tube sound. Converse to the above, I find virtually all tube amps have a "rounded" sound that flat 20hz-20khz response doesn't get at. I suspect tha the more rolled nature (with subsequent phase shift) of the high and low ends of tube amps has something to do with why we perceive this. I know of at least two solid state amps that specifically also roll off about the same as a tube amp, which tend to share a bit of this characteristic. 3) "It's next door, and it's real" presence. A favorite test of mine when considering a new component in my system, and I have used it to build that system. With a really good sound source, acoustically played and recoreded and "three dimensional" in-room, walk out of the room....despite frequency response no longer being much of a factor...some components convey a "they are in the other room" feeling, and with some the sound just sounds artificial. Of course, this is through phase-coherent, time-aligned speakers (earlyier maggies, and then and now full-range Thielfs). Components that fail this test don't make it into my system. ************************************************** ******** I'd be interested if anybody else experienced any of this, and if so, tied it to phase-coherence. |
#3
Posted to rec.audio.high-end
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LP inferior?
"Bill Noble" wrote in message
"Eeyore" wrote in message ... Bill Noble wrote: if you are sampling a sine wave (or square wave) at a single frequency, so long as your sample rate is 2X or greater than the fundamental, you will not get ALIASING of the fundamental. This says nothing about distortion of phase or waveform. If phase information is important, a significantly higher sampling rate is needed - 10X is much more typical. A control system for a large airplane, for example, had a roll off at 4 Hz - we found it necessary to sample the input data at 60 hz to prevent phase induced instability. That's 15X the maximum passband frequency. I see no reason why this kind of effect does not apply at audio frequencies as well. Because the ear is insensitive to phase info at the relevant frequencies. not clear what "relevant" means in this context, but I have run tests (decades ago), to duplicate what was widely documented, as follows: pair of headphones, single white noise source - add phase shifting network to one side only - white noise is indistinguishable via spectrum analyzer before/after (or left/right). Put on headphones. hear a tone equal to the pass band of the phase shifting network. as I recall, I did this in the 1Khz range, but I honestly don't remember. My point here is that there is significant relative phase detection capability in the pair of human ears that not commonly understood. My duplication of these experiments strongly suggests that your statement about insensitive to phase is incorrect. Your statement seems to be confusing relative phase with absolute phase. The ear is very sensitive to phase differences between two sources that are heard at the same time. For openers, there is a frequency response change due to cancellation in the air and at the ear. One source becomes the reference and we are far more sensitive to phase differences in the other channel because our ear has a reference, and the difference is relative to the reference. However, when we speak of the ear being insensitive to phase, we're talking about phase changes that affect both sources or channels identically. For example, the low pass filters in a CD player would affect both channels identically. There is no reference that is separate, so you are expecting the ear to hear an absolute difference. |
#4
Posted to rec.audio.high-end
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LP inferior?
Bill Noble wrote:
"Eeyore" wrote Bill Noble wrote: I see no reason why this kind of effect does not apply at audio frequencies as well. Because the ear is insensitive to phase info at the relevant frequencies. not clear what "relevant" means in this context, The ones claiming to be 'undersampled'. but I have run tests (decades ago), to duplicate what was widely documented, as follows: pair of headphones, single white noise source - add phase shifting network to one side only - white noise is indistinguishable via spectrum analyzer before/after (or left/right). Put on headphones. hear a tone equal to the pass band of the phase shifting network. as I recall, I did this in the 1Khz range, but I honestly don't remember. My point here is that there is significant relative phase detection capability in the pair of human ears that not commonly understood. At 1 kHz I can certainly believe that. At 15 or 20 kHz (if you hear that high still) ? How a bout checking that. My duplication of these experiments strongly suggests that your statement about insensitive to phase is incorrect. I didn't say the ear was totally insensitive to phase. That would be absurd. You misread or misunderstood my statement. Graham |
#5
Posted to rec.audio.high-end
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LP inferior?
On Tue, 25 Nov 2008 21:24:19 -0800, Harry Lavo wrote
(in article ): On Nov 25, 11:02*am, "Bill Noble" wrote: "Eeyore" wrote in message ... Bill Noble wrote: if you are sampling a sine wave (or square wave) at a single frequency, so long as your sample rate is 2X or greater than the fundamental, you will not get ALIASING of the fundamental. *This says nothing about distortion of phase or waveform. If phase information is important, a significantly higher sampling rate is needed - 10X is much more typical. *A control system for a large airplane, for example, had a roll off at 4 Hz - we found it necessary to sample the input data at 60 hz to prevent phase induced instability. That's 15X the maximum passband frequency. I see no reason why this kind of effect does not apply at audio frequencies as well. Because the ear is insensitive to phase info at the relevant frequencies. Graham not clear what "relevant" means in this context, but I have run tests (decades ago), to duplicate what was widely documented, as follows: pair of headphones, single white noise source - add phase shifting network to one side only - white noise is indistinguishable via spectrum analyzer before/after (or left/right). *Put on *headphones. *hear a tone equal to the pass band of the phase shifting network. as I recall, I did this in the 1Khz range, but I honestly don't remember. My point here is that there is significant relative phase detection capability in the pair of human ears that not commonly understood. My duplication of these experiments strongly suggests that your statement about insensitive to phase is incorrect.- Hide quoted text - - Show quoted text - I've always found it difficult to accept this notion, based on several observations as an audiophile for 50 years. Mind you, these are "speculations" but I would love to see somebody set out to verify them: 1) Extreme frequency responses. I've always felt that amps with wideband response at the low end sound more powerful and have better defined bass than their rolled-off counterparts (i'm talking below 20hz here). And likewise, I've always found amps with wideband high end to sound more realistic on triangles, cymbal after-ringing, etc. Conventional theory says one just doesn't hear these things. I've seemed to, although I will grant you it could just be a placebo effect. 2) "Rounded" tube sound. Converse to the above, I find virtually all tube amps have a "rounded" sound that flat 20hz-20khz response doesn't get at. I suspect tha the more rolled nature (with subsequent phase shift) of the high and low ends of tube amps has something to do with why we perceive this. I know of at least two solid state amps that specifically also roll off about the same as a tube amp, which tend to share a bit of this characteristic. Square wave tests of modern class AB tube amplifiers show a certain amount of roll-off at low frequencies (expected due to the output transformer), but usually show nice sharp corners indicating extended high-frequency response to at least 100KHz. 3) "It's next door, and it's real" presence. A favorite test of mine when considering a new component in my system, and I have used it to build that system. With a really good sound source, acoustically played and recoreded and "three dimensional" in-room, walk out of the room....despite frequency response no longer being much of a factor...some components convey a "they are in the other room" feeling, and with some the sound just sounds artificial. Of course, this is through phase-coherent, time-aligned speakers (earlyier maggies, and then and now full-range Thielfs). Components that fail this test don't make it into my system. Well, there is a palpability about live music that no reproduced music can match except in the grossest way. There are times when a very good stereo system MIGHT fool a passerby for a few seconds on some instruments, but in order to do that at all, the recording must be very close-up, and the ensemble must be very small or a solo instrument. Orchestras, big bands, etc, never will fool anyone, and neither will brass. There is something about the sound of live brass that simply cannot be reproduced by any audio system that I have ever heard. For one thing, speakers don't seem to be able to move as much air in the required frequency band for reproduced trumpets or trombones to have the necessary bite that says "this is real". I recall once walking down the street in an area of San Francisco famous for its night clubs (out Geary street) and passing a nondescript little joint that had its front door propped open. As I passed the door, I was hit with the sound of some jazz playing inside. I knew instantly (even though I couldn't see inside) that the music coming through that doorway was LIVE, unamplified music. I didn't need to be told, didn't need a double-blind test. My ears told me all I needed to know. I went in and spent one of the most pleasant evenings imaginable listening to a really good quintet play in that tiny bar. Real music will pull you in, Hi-Fi can't do that. ************************************************** ******** I'd be interested if anybody else experienced any of this, and if so, tied it to phase-coherence. My Martin Logans are phase coherent above 400 Hz, anyway and I have owned MG-II A, Tympani III, and MG-3B Maggies, all of which were phase coherent. While all of these speakers did some things extremely well, I never noticed that the phase coherence added anything to the palpability of the performance. |
#6
Posted to rec.audio.high-end
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LP inferior?
"Sonnova" wrote in message
My Martin Logans are phase coherent above 400 Hz, anyway and I have owned MG-II A, Tympani III, and MG-3B Maggies, all of which were phase coherent. While all of these speakers did some things extremely well, I never noticed that the phase coherence added anything to the palpability of the performance. There are many reasons for that, but probably the most important reason is that the phase coherent acoustic waves coming out of a speaker are quickly turned to mush by just about any real world listening room. IME the best way to portray a maximally-coherent sonic image in a typical listening room involves the use of loudspeakers with carefully-controlled directivity. This automatically precludes the use of dipolar planar speakers, although in some ways they are better than classic cone/dome audiophile speakers. If you want directivity control over the widest possible frequency range for a reasonable cost, the speaker system will be composed of a large direct radiator and what well-informed people call "waveguide speakers", but the general public calls "horns". One of my friends is a world-renowned expert in acoustics and loudspeaker design, who has many leading-edge papers to his credit, and has consulted on the design of a wide range of reproducers for a number of well-known manufacturers. He also owns a large stable of relevant patents that he has licensed to various manufactures. Here is his own personal line of consumer-oriented products: http://www.gedlee.com/Summa.htm I don't use speakers that much for serious listening, so I will probably never again make a large investment in speakers for my home. However, were I to do so, my next speakers would no doubt have controlled directivity. Waveguide or horn speakers have risen in favor among audiophiles, and also fallen out of favor. In the 1950s and 1960s, many high end speakers including those by Klipsch, JBL, EV, and Altec included waveguides. They often had obvious and characteristic audible flaws. The technology of acoustical waveguides made many significant technical advances during the 1980s and 1990s. Their use remains the rule for high quality sound reinforcement, so there is plenty ready money for research and development related to their design and use. The obvious characteristic audible flaws have been fully addressed for several decades. Since I am obliged to make cost-effective choices, I would probably pick my next speakers from the better commercial products designed for high quality sound reinforcement. I am currently experimenting with replacing the suffet-mounted Boston Acoustics CR-9 speakers in my living room with EV ZX-1s. The sonics of the ZX-1s (as equalized) vastly surpass the CR-9s (as equalized) in *all* ways. The comparison is probably a little unfair due to the age of the CR-9s. OTOH, the price comparison is not extreme. The basic technology of the CR-9s, which are composed of an approximate 7 inch woofer and a small dome tweeter is representative of most modern residential loudspeakers in the same price class. The ZX-1s use an 8 inch woofer and a waveguide/driver assembly. Their strong advantage in clarity is due to the fact that they have controlled directivity. I've also auditioned ZX-5s in my living room and they are of course suburb if properly equalized. My long-term choice would probably be ZX-4s as the extreme dynamic range capabilities of the ZX-5s would go unused in almost any residential listening situation. The controlled directivity down to even lower frequencies than the ZX-1 has proven to be a significant sonic advantage. |
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