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  • We couldn't really do a MIDI video without having

  • An old keyboard from the 80s, and there's nothing more iconic. I think from the 80s than Yamaha dx7

  • it's

  • Got those classic piano sounds and stuff. Let me find an organ. There was a hospice a classic I

  • Mean that they're pretty awful sounds

  • I'm not a keyboard player, but I think that was part of the advantage of MIDI is as someone that wasn't a great player and

  • didn't know a lot about sounds you could just

  • Worry about it later fix it change the sounds later on so the scope was much more than them with audio

  • But yeah the sounds were bad, then the sounds are bad. What can you do?

  • MIDI was something that was designed in the early eighties it came out in 1983, but there were earlier versions of it made by roland

  • which kind of prototypes that became midi and

  • I'd say it's kind of analogous in some ways to like a compression algorithm. It's very loosely analogous

  • So instead of say having a bass drum

  • That's recorded as an audio signal so you've got a microphone inside the bass drum, and you're playing the bass drum

  • And it would take up a lot of back in those days

  • I mean you weren't even really thinking about disk space because it wasn't being recorded digitally

  • But if it had a being it would have taken up a lot of disk space more than was possible to do

  • What you could do is you could get one of the bass drums and say well all the bass drum sounds are basically the same?

  • thing

  • What we do is

  • We'll store that one sound and then

  • play a note on a keyboard or

  • Play a note from a trigger or from a computer or something like that

  • And it would play that sound over and over again, and that was one of the many many uses of MIDI

  • But it was the idea that you control

  • your devices in the studio by little bits of

  • Information rather than containing the whole wave or whatever do you wanna do?

  • Middies an acronym isn't it is yeah it stands for musical instrument digital interface

  • Midi obviously ended up being used with computers very very early on

  • atari the st model and

  • I think a lot of other models had MIDI ports directly in on the side and because they had a graphical environment

  • Steinberg wrote Cubase I believe it was still it was Steinberg back then they wrote a piece of software called

  • Cubase which was an early MIDI sequencer which is still going today today as a full-blown

  • audio and MIDI package in fact we're probably end up using that a bit later, but back in those days you could

  • effectively create a whole composition on a computer and trigger off the sounds from various of sound modules and samplers and whatever else and and

  • It would produce these files that were maybe a captain of K in size

  • But could have a whole arrangement which back in those days was was phenomenal

  • So let's get into a bit more technical stuff in MIDI

  • there's these things called channels, so there's 16 channels which are from the

  • Users point of view numbered 1 to 16, but internally 0 to 15 for obvious reasons

  • And they basically you could see a channel as as a way of addressing different pieces of equipment

  • And there's also a mode called, Omni, which means it would listen to all channels

  • So if you wanted to say have a piece of equipment that had that just did the piano

  • Another piece of equipment that just did the drums another one that just did the bass you could

  • Set them to different channel numbers internally you could go to their settings as I only want to listen to

  • channel 3 on this particular piece of equipment and

  • Then you could have different tracks within your MIDI sequencer

  • That would only put that data to channel 3 and only put that data to channel 1. Let's say so you could have

  • effectively

  • One signal that would carry all the data for the entire song

  • This is like one set of cabling that perhaps all connected to all of the equipment. Would yeah, I mean the way

  • I mean, there's this all sorts of complicated ways of

  • cabling up MIDI with distribution boxes

  • But the the most simple way to do it would be to go out of your

  • computer or your sequencer or whatever into your keyboard and then out of the

  • keyboard out

  • Of that one to the next one or should mention at this point the actual MIDI

  • The look of MIDI cables so I mean this is the back of a focus right?

  • stereo

  • Sound card here, so as you can see the the standard MIDI in and out are the 5-pin din

  • sockets similar to the socket that was used on a tape machine to put programs into an old computer like

  • My old icon lecture on BBC, so we've linked all these machines together

  • So so one let's let's strip it down because it's all very well to say there's 16 channels as with anything

  • It's better to explain it simplified

  • So let's forget the fact. There's 16 channels

  • and just go with one channel, so let's say we've got a keyboard and a piano module and that's all we're dealing with and

  • There are five types of messages that you get

  • That MIDI can transmit and receive and the first of which which is

  • probably the most used are what's called the channel voice signals and the channel voice signals are very similar to

  • Cable signals from a computer keyboard or anything else, and if you've ever done any programming

  • or sort of dealt with anything

  • Events in JavaScript or something like that. You'd know that there's sort of Mouse down mouse up events keydown keyup

  • events and you get the same thing with keyboards

  • So the channel voice settings will say on channel 1. I'm going to send a note down, and then a note up

  • So you can record the length of the time that the note was down you can also on some cables with aftertouch say how much

  • pressure

  • Yeah, how much pressure you're applying after the event you can say how much pressure you initially touched it with the volume of the note

  • And a whole host of other things like the modulation wheel and you've then got after that channel mode signals

  • Which I'm not going to go into

  • But they're just basic satellite little reset signals and system signals and stuff like

  • And then you've got what's called a system common messages, which are things that are sent to every device in the system

  • So if you had a whole load of sound modules it send it to all of them

  • And then you've got system real-time signals, which are things like your time code in your clock

  • All that kind of stuff, and then you've got what's called system exclusive signals or see sex as they're called for short

  • which is slightly a backup and restore can be used for backup and restore functionality, so let's say you've got a sound module and

  • In that sound module you've got a load of different

  • Piano sounds and you've tweaked these piano sounds to have a certain amount of sustain and whatever and you want to save those settings

  • you can use your audio sequence or a piece of software to record the MIDI data out of that and then when you

  • dump the system exclusive data

  • It dumps that into your computer

  • and then you can retrieve it back and restore the settings on your on your module so a

  • nice easy way in the early eighties to

  • Backup and restore things amongst other things each unit that's the whole point of system exclusive that the stuff that that can do is

  • Exclusive to the individual unit MIDI sounds like it's a very useful and kind of specialist

  • application in in studios

  • And and is that was that?

  • Is that what we're talking about MIDI has been used that long because that's what it found its you

  • Well it started like that, but no I mean, it's it's used all over the place. It was this thing that came out

  • some little bit of time after the MIDI spec came out called general MIDI which kind of

  • standardized

  • What you should find on each channel so for example channel one would be a piano channel 10 was for drums and in the 80s?

  • And 90s people who were playing computer games particularly on early pcs

  • They would have had maybe a Sound Blaster card, and then that meant that say computer game

  • manufacturers could put music along with their game

  • Where they were recording the note information?

  • Again keeping the file sizes really small and then that would be fed into your sound card to create

  • whatever fully sort of symphonic

  • Piece of music you wanted in the background of the game, so if you had a really good sound card

  • But really good sounds the music on that game might sound really good

  • And if you had a really cheap sound card the music on that game could be really cheap

  • but the fun was behind it was still MIDI and

  • That was all over the place another thing that MIDI gets used for in this day and age

  • And I use it myself live when I'm gigging is

  • I have a foot controller which is MIDI and then it changes all the different sounds in my guitar rec

  • So if I'm on sound one and it's nice and clean I hit and sound too

  • And I can play a solo or whatever and it will change all the equipment and change which setting they're all on it

  • And that's called a patch

  • It's a very easy way to

  • Just hit a pedal with your foot and have all your sounds change at the same time

  • And that's also true for keyboard players

  • You know they'd be playing on a piano sound and then get a patch too

  • and it suddenly becomes an organ and it might fire off patch changes and other people in other pieces of equipment and

  • That's a just a good example of a control signal. That's sent by MIDI

  • He'll give you a demo of how a certain bit of MIDI works

  • We're just going to record something into the computer, so this is Cubase this is

  • Version 8. Which is far advanced to the version that would have been on the Atari ST back in the early 80s but?

  • Fundamentally it does exactly the same thing rather than using the dx7

  • Sounds I'm going to use a very dated sail

  • That's built into Cubase so this is controlling the computer

  • So you can see if I play the notes on the keyboard they light up on the side here

  • Let's say I'd played a note wrong heaven forbid I did that so

  • Okay, so I've got the notes wrong there

  • and I hit a little fumbled bit at the end and I could double click on this and go oh, there's a

  • Fumbled note there, so I'm getting rid of that

  • And I can move these notes to where they should be and then I could play that back, and it should be fixed

  • Which still sounds bad, but is her infinitely better than it was before when it was on the wrong note, so

  • You can see the data is getting in and the data is being stored in the computer as

  • Messages of note on a note off and the color here and represented with these bars at the bottom as well

  • represent the volume

  • I played the note on the technical side so obviously we're seeing a bit of kind of user end data here

  • What does a message look like right well we can get into that that's funny. You say that the reason I?

  • When I first started using MIDI I was maybe about 13 or 14, it's gone

  • I was entirely from the user end and then through my career working in the studio

  • I was using entirely a user end and I didn't really think about how it works

  • I just thought about the channels and the messages I kind of knew what they meant

  • but I didn't really care about that too much, and then something came up where I was writing a

  • video server application that needed to sync up with timecode

  • so I had to write a timecode reader and

  • in the process of doing that I actually had to start intercepting MIDI messages and

  • Looking into what they actually contained

  • So I've modified that time code reader program that I wrote

  • So we can actually capture into a text file what's going on, so if I just play a note and then

  • I let you go

  • so we should now just have one note on one off so if I like this MIDI output dot txt and

  • We can see I played note 72 with a volume of

  • 91 they're not actually 72 or

  • see one of that is in hexadecimal so

  • Whatever they are in in decimal that's what I played and

  • We got a note on signal there and another note on signal there 0 which is denoting that it's a note off

  • Ignore the rest of it. This is actually what's called the midi clock, so it's telling me

  • What the the number of the messages of C messages come in and you want to make sure that the message that comes in is?

  • After the previous one and such so that's that's what that is there the zero is the channel

  • That it's on which means it's actually on channel one

  • Because I'll see 0 is channel 1 and 15 is channel 16

  • Just to confuse everyone so we can capture some other things as well, so if I play a note again

  • and then do the modulation wheel and

  • Then back down again, and then let go the note

  • You can now see I've got a new note on message there, and then a load of control change information

  • which is

  • Increasing 1 2 3 4 5 6 7 9 it starts skipping it gets bigger and bigger and bigger until it reaches the top

  • It goes back down the other side back down to 0 again

  • So that is literally the recording of me pushing up the modulation wheel and bringing it back down again

  • And that just makes it this is a technical term sound Wibbly

  • Well the modulation wheel will do whatever the sound module is is set there's also a

  • Pitch shift wheel which will make these you

  • Know you go up and down in pitch or whatever so

  • There's all these different controls

  • There's panning so you can get things to go from left to right in the speakers and all of those things will be

  • recorded by your MIDI sequencer and then reproduced ok

  • And then you were mentioned before about kind of controlling and synchronizing things that to meet a really good example

  • Of something that MIDI does well, but also shows off kind of how archaic it is

  • Because you think with the technology in today's time

  • You could send a full clock which will be hours minutes seconds frames all in one bit of data

  • Not literally one bit of data in one chunk of data

  • and

  • It should be able to just pick up on it in real time, but back in the day

  • That was too much data to send through in in one piece

  • So it was broke into lots of individual pieces that were constantly sent

  • And and this is the this is the way I discovered it by having to write a time code reader

  • So let me first show you time code working

  • with their so right yeah, I've just connected the MIDI out to this and

  • This here is connected to my laptop, which is running Reaper, which is just an audio

  • sequencer

  • Audio MIDI sequencer same as key base

  • But it's only about 16 pounds or so just getting it so just here

  • you can see that the timecode is running if I stop that again, and I run my

  • time code reader software

  • So what I'm going to do now is I'm going to hit go on my laptop which will start sending

  • Timecode via MIDI to my desktop computer which is going to be and the signals are going to be recorded into the text file

  • So we can have a look at them

  • so here we go play a

  • few seconds of this and then what I'm going to do is jump this forward

  • So it's a bit further in so I'll go to there and now we're at ten minutes

  • And I'll record a bit of that, and I'm going to hit stop on there

  • And we can have a look at the text file and see what it contains

  • I'll give you a breakdown of what all of these things mean this here is the?

  • Timestamp of the MIDI signal so this here is the actual signal that's coming in for lots of 8-bit

  • Represented in hexadecimal that first one the f1 basically means that it's timecode

  • That's what that means so we can ignore that we can also ignore the last two because that doesn't contain anything

  • That's useful to timecode so it's this second number here

  • Which I've actually split into its binary representation into two columns of four and the reason I've done that is

  • Because the first column of four says what it is what it's representing so the zero zero zero zero

  • represents the number of frames

  • but because

  • You've only got four zeros to represent the number of frames

  • that can only be a value between naught and fifteen and

  • We know that when you're dealing with frames or other in twenty four twenty five thirty

  • 29.97 thirty Corley thirty

  • C30 can't be represented in naught to 15 so the next signal there

  • Which is not one gives you an offset so if that ends with?

  • One which is just one so if that becomes a one then basically you can kind of put that on before there and that

  • steps it up sixteen and the same is true for the

  • Seconds because they're up to sixty same is true for the minutes and the same is also true for the hours

  • So you've got eight bits

  • That have to tell you what part of the the time it is on that time

  • Yes

  • So so basically you you you take the four of the first four of the ones and zeroes and say this is

  • This is say hours, or minutes or the offset as I call it the offset of the hours or the offset of the minutes

  • So the way a timecode signal would work is basically you have eight different

  • Signals that come in and they all contain a little bit of the time, so let's start with

  • the first signal come in that will be zero zero zero zero

  • Which will be the number of frames and then?

  • One which will be called the offset?

  • For frames so the second bunch of four will be the frame number, so let's say it was frame number two

  • That's going to be our one. Oh because of C. It's one two four eight in the columns then

  • Your offset frames would be zero zero zero zero, but if you wanted it to be frame

  • 18 you'd actually change that to a 1 so B zero zero zero one in the offset frames

  • Which would say are your first signal isn't 2 because that effectively gets moved up to there and becomes, Oro?

  • 100

  • 108 eeen but that's sent in two separate messages the same is true for minutes

  • Seconds hours, whatever so to send a whole time yet requires eight messages

  • This is a good representation of something which is very very solid, but works really well and clearly it works

  • Well because it is everywhere whether you or working with syncing up

  • Sequences in audio or whether you're syncing up a video server to you know a band

  • That's playing and you want the videos to appear exactly the same time the band might be playing to a click track and the lighting

  • Desk might turn all the lights on at that exact moment in the show Sammy

  • It's used to do like so and it's very solid and it works almost

  • perfectly

  • You know unless you get someone pulls a cable out which just happens, and then it will goes wrong

  • But it's also very archaic. You can see with this sort of split message

  • System that seems to be going on you

  • Do have a MIDI you do have things that are long messages and short messages

  • And it takes up eight short messages to produce a full piece of timecode

  • When you hit go initially it actually sings a long message through which does contain the entire timecode?

  • But I'd imagine you can't send as many of them

  • And it's inefficient to send as many of them because you you don't need to know that once you've got a full time

  • and you're going you can then update the

  • Seconds and the frames you don't really need to update the whole time, so they sending it through in chunks

  • So I'd imagine a lot of it was written with

  • You know the computing power of the time in mind and obviously they wanted it to be compatible with most computers, which is why they?

  • chose it to run at one megahertz as a musician and any other musician should know this D minor is of course the

  • saddest of all keys

  • And I thought what is sadder then

  • Than the piece of software that the D minor chord is going to open now. This is a example of

  • Application of MIDI for something it's totally useless, but when I apply a D minor

  • Are these Internet Explorer Bing

  • As this yours is keyboard

  • no, it's

  • This keyboard I borrowed from my old

  • GCSE and a-level physics teacher

  • Phil Cummings who was

  • One of the cooler teachers at school cause he played keyboards in a band

  • but there's something about a Yamaha dx7 which just conjures up a

  • teaser yeah

  • It's just got that sound of Oh

  • Oh Internet Explorer's opened again

  • I just I play field colleagues and internet explorer open

We couldn't really do a MIDI video without having

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MIDI和數字音樂製作 - Computerphile (MIDI & Digital Music Making - Computerphile)

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    林宜悉 發佈於 2021 年 01 月 14 日
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