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In Reply to: This is silly... posted by JonB on July 28, 2002 at 17:03:09:
Your reasoning is excellent, as any beat tones produced in the audible range could be recorded on a CD. However, where the beat tones come from is another matter.Some researchers discovered that the presence of the ultrasonic components was not audible if the ultrasonics and the audible signal were produced by different speakers. It seems that the intermodulation distortion produced by the interaction of of the audible signal and the ultrasonic signal was audible. However, when the intermodulation distortion was removed by using separate speakers, the test subjects could not disprove the null hypothesis in the DBTs.
Reference: Ashikara Kaoru and Kiryu Shogo, "Detection threshold for tones above 22 kHz," Audio Engineering Society Convention Paper 5401, presented at the 110th Convention, 2001 May 12-15, Amsterdam, The Netherlands.
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"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
Follow Ups:
That's all very interesting but the question is not the audibility of ultrasonic frequencies but whether or not SACD playback benefits from 50khz-capable speakers. I say no and it is easy enough to test. First, listen to an SACD on a 50khz-capable audio system, Then, listen the same SACD on the same system with the addition of a quality low-pass filter with a 20khz cut-off. If the presence or absence of the filter is undetectable when listen to CD or LP sources, I predict that it will be undetectable when listening to SACD sources.
I do not see how your scenario fails to be concerned with the audibility of ultrasonics. Technically, one could argue that the speakers capable of reproducing ultrasonics were more accurate; but if the question is what is heard, then it does not seem to be the ultrasonics but distortion products produced in the audible range.It would be possible to have an SACD or DVD-A which would contain ultrasonic frequencies. One could record the test frequencies used, for example, which resulted in the speakers producing sufficient intermodulation distortion to be audible. So, merely introducing a filter could result in an audible change due to the reduction in the distortion, not accuracy in reproducing the high frequencies. The ready explanation would be that the audible difference was due to distortion in the speaker--in other words, something caused by the speaker, not the original signal.
One might prefer the result, of course. Some people prefer some kinds of distortion.
____________________________________________________________
"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
Back in the early 1950's (US Army) and in the past few years (CalTec), it was shown that humans can percieve signal material above the accepted limit of human hearing (generaly 20khz). The tests played material first with and then without ultrasonic content. The absence of the ultrasonic content was noticed though was not specificly identified. Theory is that while we do not consciously recognise ultrasonic material, the presense of same still excites our hearing mechanism and causes impulses to be sent to the auditory portion of our brains. On a subconscious level, we are "aware" even if we can not verbalise what we are aware of.I think we all agree that the brick wall filter of 16/44 Red Book cuts off ultrasonic harmonic information, to the detriment of sound (lets not even get into to distorions produced as harmonics are reflected back off of the brick wall filter).
Original master tapes, made before digital mastering was prevalent, contained sonic information above 20khz. Analogue equipment IS capable of reproducing the ultrasonic content (yes even tube amps and phono cartridges) of the master tapes. If speakers can be made to reproduce the ultrasonic spectrum cleanly, shouldn't that be a benefit ?
As for SACD- Stereophile was kind enough to publish spectra content of SACD and previosly of their own recordings (that they have released), both clearly showed harmonic content above 20khz.
As we go forward into higher resolution digital, ultrasonic content will become the norm rather than the exception.
Best,
But are you hearing the ultrasonics or simply intermodulation distortion in the speakers?
____________________________________________________________
"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
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