Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site dsd.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!umcp-cs!gymble!lll-crg!dual!amdcad!fortune!dsd!riner From: riner@dsd.UUCP (john riner) Newsgroups: net.audio Subject: Re: Wanted: cassette deck advice! Message-ID: <417@dsd.UUCP> Date: Tue, 5-Mar-85 14:17:25 EST Article-I.D.: dsd.417 Posted: Tue Mar 5 14:17:25 1985 Date-Received: Sat, 9-Mar-85 19:24:40 EST References: <4846@cbscc.UUCP> <> <316@cubsvax.UUCP> <8731@brl-tgr.ARPA> Organization: AMPEX DSD, Redwood City, CA. Lines: 63 > > > > Several years ago I read an article, though I forget where, in which a Nak > > engineer claimed that Nak used to do something different from most other > > cassette deck manufacturers -- I don't remember whether it was head > > alignment, > > bias, or what -- but that there is now a standard that all mfgrs. adhere to. > > > I would expect that it is EQ. Bias affects what is recorded on the tape > and shouldn't affect the playback at all (i.e. if the bias is wrong it > should sound equally bad on all decks). I have a hard time believing > that head alignment would do it either. When you adjust head alignment > you go for nice right angles and centered on the track. When you adjust > EQ, you have to pick some standard. In many radio stations, they are free > to pick whatever they want since they matching record and playback EQ's and > never deal with any serious outside tapes. Years (many) ago recorders were set up by measuring the record head current and setting the bias and record currents to a set level which (due to the limited performance achievable with the heads and tape then available) was supposed to set the flux level on the tape. The reproduce equalization was then set for the response/noise level desired. When incompatability became a problem (as mfrs and users began to understand more and the heads and tape became better) standards were developed which specified a reproduce response curve which was fixed and the record current, bias and equalization (yes there is record equalization) were adjusted to make the frequency response and distortion meet the system specifications. Several different schemes were developed to meet various system performance requirements. Eventually the NAB developed a set of standards for equalization and these are fairly well adhered to today. The present method used is to reproduce a "standard" tape (a tape made with a known flux level recording) and adjust the azimuth for peak output at the highest frequency on the test tape then adjust the reproduce response for flat output versus frequency. Then the bias is set for peak output of a signal at a mid frequency (rule of thumb is to use the same frequency in KHz as the tape speed in Inches per second up to 7.5 Khz at 7-1/2, 15, and 30 ips) and then set the record level for the distortion level at 1KHz or so. The bias and record level are then "trimmed" to compromise frequency response and distortion. Basically this applies to cassettes as well as reel to reel recorders. I have heard many comments on and off the net about Nak incompatability and I have found no definative answer but here is what I believe is the case. In order to optimize their product they used some record equalization which was meant to operate with their heads (which from what I have been able to deduce are very good) better than "standard" equalization. Since their products are generally used with high performance tape (less distortion at higher record levels), they could reduce the record level slightly at higher frequencies and get wider response at higher record levels which enhanced the signal to noise level and the spec sheet. This would produce a rolloff in the high end when played back on another mfrs tape deck. To my knowledge this is no longer the case and any incompatability is probably due to misalignment in on or the other of the machines. I don't know if this clears up any of the confusion (it probably only creates more) but I remain convinced that the notion of standards is only an illusion anyway (have you ever found a "standard" RS-232 connection to anything) John Riner AMPEX Corp. -- John Riner UUCP: !fortune!dsd!riner AMPEX Corp Redwood City, CA. Nobody knows what I am talking about, so these must be my opinions and not theirs.