Talk:Modified frequency modulation

message: The article says "MFM allows more than one symbol per flux transition — up to three — giving greater density of data than FM."  I think this is nonsense.  FM encodes a one as a 11 and a zero as 10.  MFM encoding is as shown.  They have the same density, given the same clocking; each takes two "possible transition" periods to encode a bit.  The reason MFM achieves greater data density is it can be clocked at twice the rate (because there are never two transitions in a row).  Or am I totally off-base here?  See http://www.storagereview.com/guide2000/ref/hdd/geom/dataMFM.html
Nybbler 23:29, 5 March 2006 (UTC)
replies: text: It may be confusing, but I think the statement is correct. Your statement is also correct. Mirror Vax 00:34, 6 March 2006 (UTC)
replies: text:  I'm still not seeing it.  A one followed by a zero is 0100, two bits with one flux transition.  A zero followed by a zero is 1010 or 0010 two bits and one or two transitions.  A one followed by a one is 0101, two bits and two flux transitions.  A zero followed by a one is 0001 or 1001, again two bits and one or two flux transitions.  There's never three symbols with one flux transition.
Nybbler 15:28, 6 March 2006 (UTC)
thread_title: Symbols per flux transition

message: It would be nice if the question marks in the examples would be explained somewhere. --89.49.249.90 22:13, 17 August 2007 (UTC)
thread_title:  Questionable question marks in the examples 

message: Can someone double check the illustrations?, when I study them in detail. They just don't seem to make sense! Esp, a "clock" signal of 11000000 seems weird. It ought to be 10101010 ? Electron9 (talk) 17:22, 5 May 2009 (UTC)
thread_title:  Verify the illustrations? 

message: I vaguely remember that bit-order on floppies (may ST-506 HDD, too) was LSB first. If anyone knows that for sure, it would be nice to put it here for reference.  —Preceding unsigned comment added by 91.187.225.16 (talk) 08:08, 31 October 2010 (UTC)
replies: text: Here's the signal from my floppy drive that I'm working on right now (top track, signal; bottom track, sync). It is clearly MSB first -- Wesha (talk) 22:34, 22 April 2020 (UTC)
thread_title:  BIT order on media 

message: It's not obvious to me whether MFM applies to the analog or digital world.  "Pure" FM is clearly an analogy phenomenon, whereas the article discusses streams of bit symbols, which is clearly digital in nature.  So where does that leave MFM?  Is it an analog technique that happens to have digital applications, or is it a strictly digital technique?  — Preceding unsigned comment added by 70.247.162.60 (talk) 04:18, 18 November 2015 (UTC)
replies: text: For the precursor of MFM, called FM, delay code or digital FM are better names. It is just a digital signal, not an analog one, which is why delay code or digital frequency modulation are much better terms. For MFM the same applies: it is a purely digital signal. This should also be taken care of if the merge of the MFM and delay code articles is to happen.87.179.128.35 (talk) 02:23, 26 January 2017 (UTC)
thread_title:  Digital signal? 

message: The lead says:
And now since the merge, delay encoding is discussed. This delay encoding is MFM, right? So is somehow the difference between FM and MFM the difference between delay coding and delay encoding? I get the feeling delay coding is a different way of saying delay encoding, and the lead is simply wrong: FM is Differential Manchester encoding and MFM is delay coding is delay encoding. If I'm right, we should change the lead to
It also couldn't hurt to be more explicit that delay encoding is actualy MFM; the current merger doesn't make this obvious to the reader. Digital Brains (talk) 13:47, 5 February 2018 (UTC)
thread_title:  Delay (en)coding 

message: has attempted to add fragments of recording channel design to this article which I have reverted both on the basis that they were incomplete and inappropriate to this article.  The lede accurately states that the "the minimum spacing between flux transitions that is a property of the disk, head and channel design, ..."  An article on recording theory might note that the isolated pulse is a function of gap length, flying height and media thickness.  The isolated pulse shape along with signal to noise (including off track signal) and data separator stability all go into the code chosen which has a minimum and maximum number code zeros between code ones.  This is all summarized in the lede and adding parts of this complex subject into the body is inappropriate.  I note that none of this appears in the Run-length limited article which is the parent category to this article on MFM.  It doesn't even appear in Magnetic recording.  WikiPedia would be improved by a magnetic recording theory section possibly in Magnetic storage#Design which could be linked from this article put the partial details that Myrtonos has added simply don't belong here.  TMI for this article! Tom94022 (talk) 17:39, 26 May 2018 (UTC)
replies: text: The relation between frequency and playback output is why the recorded signal needs to be D.C free.--Myrtonos (talk) 11:36, 27 May 2018 (UTC)
replies: text: I'm not sure what this has to do with the edits removed, but is it even true?  The MFM recording of  "B6DB6D..." is not DC free which is why magnetic disk recording channels differentiate.  Tom94022 (talk) 19:03, 27 May 2018 (UTC)
thread_title:  How much recording technology is appropriate to this article 

message: I'm investigating my old floppy disks right now, and I totally do not see a "missing sync bit" in the A1 sector marker this (and some other) article are talking about. Help? (top track, signal from the disk; bottom track, meander manually added for reference that's supposed to represent the real sync signal)-- Wesha (talk) 22:38, 22 April 2020 (UTC)
replies: text: OK, maybe I'm starting to understand. In terms of signal, "flux" is transition of low to high or high to low, so LH or HL constitutes a flux, and HH or LL do not. The actual recording on the track is  (or the reverse) which according to MFM rules means  but the catch is the  part, as the signal was supposed to flip there (). -- Wesha (talk) 17:44, 23 April 2020 (UTC)
thread_title:  Missing sync in A1 marker???