Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 exptools 1/6/84; site ihu1g.UUCP Path: utzoo!watmath!clyde!burl!hou3c!hocda!houxm!ihnp4!ihu1g!fish From: fish@ihu1g.UUCP (Bob Fishell) Newsgroups: net.audio Subject: Re: EQ question Message-ID: <240@ihu1g.UUCP> Date: Wed, 7-Mar-84 14:48:25 EST Article-I.D.: ihu1g.240 Posted: Wed Mar 7 14:48:25 1984 Date-Received: Thu, 8-Mar-84 08:37:35 EST References: <1534@burdvax.UUCP> Organization: AT&T Bell Labs, Naperville, IL Lines: 37 (oo) AC theory has been a while, but here goes: The 120 uS and 70 uS EQ figures you refer to are the time constants of simple RC highpass/lowpass filters used for preemphasis and deemphasis of FM broadcasts, and in tape decks. A highpass filter looks like this: O-----|(---*---O C | > R > > | O----------*---O And a lowpass looks like this: O--VVVVV---*---O R | _|_ C '|` | O----------*---O I don't remember the equations, but they're pretty simple to look up. The important thing to remember is that the greater the time constant (R*C), the greater the degree of preemphasis/deemphasis present in the system. For FM systems, the corner frequency of the preemphasis curve is about 5Khz. I don't know offhand what it is for Dolby. Standard FM uses 120 uS preemphasis; Dolby uses 70uS. -- Bob Fishell ihnp4!ihu1g!fish