Xref: utzoo rec.music.makers:9570 rec.music.synth:14893 comp.music:1659 Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!ucsd!sdcc6!ee299bw From: ee299bw@sdcc6.ucsd.edu (Unbroken Chain) Newsgroups: rec.music.makers,rec.music.synth,comp.music Subject: Re: dbx vs. Dolby C Noise Reduction Message-ID: <12001@sdcc6.ucsd.edu> Date: 24 Jul 90 16:27:38 GMT References: <827@bilver.UUCP> Followup-To: rec.music.makers Organization: University of California, San Diego Lines: 29 In article <827@bilver.UUCP> alex@bilver.UUCP (Alex Matulich) writes: >A compander basically consists of a variable-gain amplifier and a level >detector. The playback expander knows when and how much to expand by >comparing the signal to a refernece level, usually the -5 dB VU level. > [...] >adjust the playback level. Mine has a calibration control where you >record a -5 dB 1 KHz tone on a tape, play it back, tweak a trimmer pot, >and repeat until the playback level is -5 dB. With dbx, unity gain occurs at 0 dB. As it turns out, the calibration of this is not super critical, as dbx's behavior is linear. That is, the difference between any two signal levels is doubled on expansion. The Dolby schemes are different - Dolby's behavior is dependent upon signal level and varies across the audio spectrum. Therefore, calibration is critical because mistraking Dolby will either not expand and deemphasize high frequencies enough, or it over-expand and overly deemphasize them.... hence the urban legend that Dolby NR merely removes all high frequency content. Dave -- *********************** Dave Chesavage **************************** * dchesavage@ucsd.edu * * "Earth is 99% full. Please delete anyone you can." *