mo@seismo.UUCP (Mike O'Dell) (11/30/83)
Even if I cannot hear ultrasonic sinusoids free-standing, I certainly CAN tell the difference between a 12KHz sine wave and a 12KHz square wave, and that means SOMETHING is happening to some 36 KHz energy. Moreover, what makes the difference between a cymbal crash with a clearly-defined sizzle, and one which sounds like trash-can lids banged together (low-fi trashcan lids)? Overtones, my friends. You cannot have fast rise-times without lots of overtones, and you don't get good reproduction unless you can reproduce the rise-times in transients like triangles, cymbals, snare-drum attacks, and even some high-end piano work, not to mention pipe organs and synthesizers. The current CD standards are purest crap. We need 250 Ksamples/second minimum, and 16 bits minimum. None of this 14-bit non-linear crap. Remember, the Nyquist frequency is 2f only for pure sinusoids sampled infinitely long. Music recordings are poor approximations to those boundary conditions. "Get that digital crap out of here!" -Mike O'Dell
gregr@tekig1.UUCP (Greg Rogers) (12/04/83)
If you really can hear the difference between a 12khz sinewave and a 12khz squarewave would you please list the conditions of your test. This would be a service to all researchers in this field because earlier scientifically controlled tests contradict your claims (consult back issues of AES Journal). I suspect however that what your are really hearing is distorsion produced by your loudspeaker/headphones created by trying to reproduce the ultrasonic frequency components contained in a squarewave produced by a signal generator. Squarewaves of this type do not occur in recorded music unless they are produced electronically (note this still doesn't mean you can hear them, only that they exist on the recording). To take this onestep farther, I know of no studio tape recorder that can come anywhere near recording a 12KHZ squarewave accurately or any disc cutting system that could transfer it to a record. Hence I'm afraid that even if you were able to satisfactorly demonstrate the ability you claim you would be hard pressed to find anything to listen to. Anyway I'm very serious, PLEASE publish your test conditions and data. Now in the tone of your remarks -- I have a hard time believing that you really understand or know what sample rate or bit resolution that you would find acceptable since from your final remarks about digital signal processing you obviously lack knowledge of this discipline. Greg Rogers Tektronix (still amazed)