From: utzoo!decvax!harpo!npoiv!alice!rabbit!jj Newsgroups: net.audio Title: Re: New technologies Article-I.D.: rabbit.627 Posted: Sat Jul 24 22:05:40 1982 Received: Tue Jul 27 01:18:05 1982 References: utcsrgv.477 F E H !!! Replying to the article which bears this article's head. 1) Direct drive turntables do NOT have more low frequency noise than belt drive turntables. What they DO have is "cogging" distortion, so named for the stepping motor's tendency to provide an impulse every t sub s seconds. This impulse does two things: a) It propigates through the entire platter system, causing noise pickup at a frequency which is NOT low, and b) It causes a very slight FM modulation of the material being reproduced. This effect "seems" to be the cause of most dislike of direct drive turntable, in fact, it is responsible for the 'unique' sound of several of the direct drive breed. There are a few turntables using quadrature drive that do not have this problem. Strangely enough, they sound a lot like a belt drive turntable. The IM and sideband properties of this kind of modulation are mind boggling. Try it yourself. Non-the-less, I still wonder what is wrong with a servo'ed BELT drive. It has the advantages of both systems, and few of the problems. Its only problem is its belt, and that is common to all belt drives (funny thing!). 2) "Class A" amplifiers have been touted in the high end market for a long time. REgardless of advertising noise, class a is class a. If the output device doesn't conduct linearly through the whole cycle, it ain't class a. There have been several important new designs in the biasing of NON class A amplifiers lately, but these amps are not in the high end market, they don't need to be. There is NO reason why any amplifier has to be in the high end market. 3) There are several untruths listed under this head. I will cover a couple. a). The filter doesn't have to have an instantanious change from on to off. In most cases, the sampling rates are chosen to be ABOVE! the Nyquist frequency far enough that the filters are not that difficult to design. In fact, that is usually the one thing that constrains the sampling rate. b). D/A conversion, since the advent of the digital audio "threat" has been pushed quite a ways. The D/A that cost 300 $ ten years ago now costs $80 and works better. If a 16 bit D/A introduces noise above -96dB, it isn't a 16 bit D/A, by definition. The A/D and D/A introduce noise only as they quantize the signal to 16 bits. If they do otherwise, they should be replaced with a relatively inexpensive unit that WILL work right. So much for that. The signal coming into the A/D may not have 16 bits resolution, but it isn't any worse than the same signal that is being used for disc or tape, so that arugement is handwaving. c). The idea that digital has a lower signal to noise ratio for lower energy signals is true. So does everything else. If the Signal to Noise Ratio (SNR) is better, then the noise will be less troublesome, if the noise is of the same (white) type. Disc's, tape, and the like have exactly the same behavior, except that the signal disappears at a higher level, indicating that the noise is causing MORE damage. As far as standardazation, I couldn't agree more. There are several systems (Phillips has suporters in Japan, BTW) where there should be one. The reasons don't even have to do with competition. I could flame for hours about that. On the other hand, quad doesn't have much to do with digital, as far as public acceptance is concerned. I have listened to quad setups, and I don't like them very much. A proper stereo system sounds more realistic to me than a quad recording, even including ambiance. I'm not convinced that quad is better. I am convinced that a record that doesn't lose high frequencies when it's played, doesn't automatically introduce 3% distortion, and is washable if it gets dirty, has much to offer. Especially since it sounds so much better. Now-- If we could only raise Stowkowski for a few recording sessions. J.D.Johnston rabbit!jj BTL/MH