Xref: utzoo rec.music.makers:9734 rec.music.synth:15119 comp.music:1724 Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!xylogics!merk!alliant!muller From: muller@Alliant.COM (Jim Muller) Newsgroups: rec.music.makers,rec.music.synth,comp.music Subject: Re: dbx vs. Dolby C Noise Reduction Message-ID: <4035@alliant.Alliant.COM> Date: 2 Aug 90 22:03:22 GMT References: Reply-To: muller@alliant.Alliant.COM (Jim Muller) Distribution: na Organization: Alliant Computer Systems, Littleton, MA Lines: 31 In article rich@sendai.ann-arbor.mi.us writes: > dbx > - If it uses a dynamic gain device, then: > - How does the playback expander know when and by how much to expand? > - Is there a separate control signal recorded that is used to > dynamically adjust playback level? >Don't know. This has been answered before, but... In general, expansion on playback uses the signal itself compared an aboslute reference level. There is no control signal. I am not sure exactly what dbx per se does. > Dolby C >My understanding is this... Dolby B is much like an enhancer in that >it boosts the highs before putting them on tape. Then on playback, B >cuts them again. My understanding is that Dolby C is much like Dolby >B applied twice to the same signal. No. It *can't* work that way. If that was all there was to it, you could just establish an appropriate EQ curve and use it. In fact, you should already be trying to saturate the tape, so just boosting the highs on recording and reducing them on playback will saturate things more. There must be some dynamic effect, but there is some question of what frequencies you are using to measure your level and whether you compress all the frequencies. This is the basic difference between Dolby B and C, and possibly dbx too. Maybe someone should post that again? I know it just went up a few weeks ago, but... AAAAAaaaaarrgh! -- - Jim Muller