The way I've always explained it is that it is trickery to get the audience from one tempo to another.
A fact that I haven't seen anyone point out? Did they notice? I'm not sure. Because it seems instead they're very, very hyper focused on explaining why it's much more complicated than you think it is. Completely ignoring the Big Thing Going On, the tempo change.
The reason I'm motivated to write this is because a couple videos just tell you point blank "you're perceiving it wrong".
Which is effectively the same thing as saying that Led Zeppelin made a mistake! Everyone that likes the song and that part of the song - you don't even know what you're hearing! Wait! You might not like it, or like it better, once you hear X YouTube expert's explanation of how it really is! You're counting it wrong, the pulse is not what you think it is!
Here's my expert opinion, for free like their explanation:
The Dsus4 "fanfare" part comes in a touch late. Deliberately. The first time around is 88 bpm in 4/4, deceptively DROPS A BEAT before switching to the C. It picks up tempo to about 92 bpm. The C then deceptively goes an EXTRA 16th (perceived by the audience as effectively a "short beat") before going back to the Dsus4 fanfare (now at 92 bpm) which again drops a beat back to C - which this time continues at a faster 96 bpm, and Bonham puts the snare on the & of 2 - which is congruent with where Page put accents on the C, but then gives you beat 4 on the snare; at this point the AUDIENCE has been shifted to the 98 bpm speed.
Also note the drums go away on the C chord: you can decide to count that however you wish based on the pulse of the strumming (including one guy that wants it to effectively be perceived as reggae...); but it's how the guy walking down the street who knows nothing about time signatures perceives it that actually (pun intended) "counts"! That Invisible Listener's Foot is where the pulse is.
But feel free to hear it as reggae, or some sort of odd West African poly rhythm if that's your fancy. In reality, NOBODY who isn't a musician COUNTS when listening to music. Nor do most good rock musicians unless something is really amiss.
POINTS TO CONSIDER I BELIEVE PEOPLE ARE MISSING:
"Deliberately". I've seen a video where someone insists it's a mistake. Most all ignore that there are ebbs and flows timing wise - which is the essence of John Bonham's feel. There are people who will insist music that isn't perfectly gridded - perfectly on beat - is therefore "wrong". This is an edict invented by people who don't want to make a judgement call on the reality that some music pushes the beat, some drags the beat, sometimes a mix. Or least it was until the computer recording era came along.
"Deceptively". It is an artistic decision to make this part feel like something happened different, and was abrupt. They want to disturb the AUDIENCES inner metronome. The effect of the sensation of being abrupt, something happened "early" is what is wanted.
This is why I say it's not a time signature change! If you're perceiving a different time signature then you KNOW there is going to be a missing or added beat. The fanfare is 2 measures in the song, the first of which went (deceptively ) as expected for 4 beats, the second time dropping beat is NOT "dood, a measure of 5/4". It's NOT a big measure of 7 (the rhythmic pattern REPEATS TWICE).
It's very simple: they DROP A BEAT. There is a difference: in an odd time you expect a beat to go away or return. You know it's an "odd time signature" - that's the point. I would guess that people accustomed to the odd time of the Zeppelin songs "Black Dog", "Four Sticks" and "The Ocean" want this to conform to that creative notion. It's not, it is deliberate musical deception! And "in ye olde days" music as an art form wasn't that coarse; it would have been crass to have Yet Another Odd Time Signature with The Drummer Playing Across the Bar/Backwards/Poly/Syncopated.
Because they've thrown the AUDIENCE off kilter they can sneak the tempo up a bit. Which I claim was the point.
When they return to the fanfare - at the faster tempo - the audience now expects it to be short. Of course! So then they make the following C continue where the audience would also expect it to go the same extra beat as before - a surprise. It also lets the guitar get away with accenting that cues the end tempo of about 98-99 bpm, and Bonham puts the drum-stamp of approval on beat 4 - but only after one last bit of deception with the snare hitting the & of 2:
in rock music the snare "always" accents 2 and 4. The AUDIENCE is expected to perceive the & of 2 as a new beat 2 - or was it beat 4? That ambiguity is the final step, closed by him hitting the snare on 4 afterwards. BUT, because the & of 2 is after beat 2, a shorter length of time between the "traditional" 2 and 4 has occurred: the listener is pushed "forward", "faster".
It would seem "a lot" of people want "the tempo change" to happen at that moment.
This is a very curious thing to me. Even as a child I heard this section of the song pushing the tempo faster (as other sections do as well). Yet, effectively all of these videos have one problem in common: they want the tempo to remain steady from before the fanfare section through to the guitar solo!
Which means, they all want to do some crazy math to reconcile both beats being dropped and added, as well as the slightly late start, and the "early"-ish, 16th-ish change back to the fanfare the second rep, and the accelerondo at the intro to the guitar solo.
Some guys want to count all the way across all sections, as if nothing repeats.
Some want to add the fanfare reps into one measure of 9 beats.
Some want the pulse to be 16ths on the C chord parts to account for the 16th coming back to the fanfare.
Some want the listener to perceive it as syncopation to an invisible pseudo-clave pulse.
Some have zanier ideas about it.
Here's my beef: they all ignore what really should be the most important concept to the notion of "music theory": the only thing that matters is
AUDIENCE PERCEPTION
The mythical imaginary listener may not be able to use musical terms to explain their perception, but that doesn't mean they don't perceive.
Music is not science! It is SUBJECTIVE. It is the most absurd thing in the world to tell an audience "no, you're not perceiving it right". That's like insisting cerulean blue in a painting of a sky is ACTUALLY green, "you're just not perceiving it right". The only thing that matters is perception of the audience. One can count odd times over anything and insist that's what one is perceiving, but it doesn't matter.
I will invoke Reverse Speculative Musical Anthropology and suggest that Page/John Paul Jones had 3 separate "songs" and decided to stick them together as an opus. They had a problem: the 3 parts were different speeds. They had to connect them together.
They did that in the "bridge" section very cleverly. So cleverly that the Scientists of Music do not agree on what is actually happening. My addition to this pointless affair (because in reality, do you like it or not?) is that you can't remove the AUDIENCE PERCEPTION from the explanation. Call it "Chip's Audience Perception Rule".
YOU CAN'T TAKE AUDIENCE PERCEPTION AWAY.
.. is the only absolute in "music theory". When you count odd time signatures it does funny things sometimes to your perception. Fundamental "sensations" of downbeat, up and offbeat get messed around. It's confusing. Sometimes the artist WANTS that confused impression (these days.. a lot want that apparently). A blurry sensation of where the downbeat is seems the goal of a lot of prog bands, despite one of the important antecedents Rush making odd times groove being the dictate. And certainly the king of grooving odd time signatures - Soundgarden - wasn't about making you feel dizzy about the downbeat. They were all about it.
Zeppelin didn't want you to feel confused about the downbeat on these parts of the song. They wanted you to feel unsure about WHEN it was happening, not WHERE!
For the first time listener to Stairway, they're simply perceiving a beat going away, a 16th being added - and in the process being tricked about the tempo. Here's another thing: this is my opinion. Not really an explanation, because - the way you perceive it is reality. I'm sure there are people that won't, or can't hear it as a tempo change with beats added/subtracted (which is the problem...). But in my OPINION the above is what is going on in reality.
$.10, thanks drive through.
