Music: what's in this chord?

Question

Input

The symbol of any triadic chord (see http://en.wikipedia.org/wiki/Chord_(music)#Triads).

Output

The notes constituting the given chord.

Examples

Input: AM Output: A C# E

Input: C#m Output: C# E G#

Input: Db+ Output: C# F A

Input: C0 Output: C D# F#

Bonuses

-50 if you can also deal with seventh chords

-150 for actually playing the sound of the chord

-150 for using printable characters to show how to play the chord on a piano; example for AM:

┌─┬─┬┬─┬─┬─┬─┬┬─┲┱─┬─┬─┲━┱┬─┲━┱─┬─┬┬─┬┬─┬─┐
│ │ ││ │ │ │ ││ ┃┃ │ │ ┃ ┃│ ┃ ┃ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ┃┃ │ │ ┃ ┃│ ┃ ┃ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ┃┃ │ │ ┃ ┃│ ┃ ┃ │ ││ ││ │ │
│ └┬┘└┬┘ │ └┬┘└┲┛┗┱┘ │ ┗┯┛└┲┛ ┃ └┬┘└┬┘└┬┘ │
│  │  │  │  │  ┃  ┃  │  │  ┃  ┃  │  │  │  │
└──┴──┴──┴──┴──┺━━┹──┴──┴──┺━━┹──┴──┴──┴──┘

-100 for using printable characters to show how to play the chord on a guitar; example for AM:

x   o   o   o   o   o
┌───┬───┬───┬───┬───┐
│   │   │   │   │   │
├───┼───┼───┼───┼───┤
│   │   │   │   │   │
├───┼───┼───┼───┼───┤
│   │   █   █   █   │
├───┼───┼───┼───┼───┤
│   │   │   │   │   │

(see https://en.wikipedia.org/wiki/Box-drawing_character)

Rules

• The result must be a command-line program or script.

• The input and output can be in any form, as long as it follows a music notation standard.

• A guitar or piano representation is considered valid if and only if it contains the three (triadic) or four (seventh) required notes and nothing else. The same note can be present several times in the chord.

• External libraries are not allowed, except for sound generation (in which case the #include, import... directives are not added to the character count).

• This is code golf, the shortest code wins!

A little bit of music theory...

In modern Western tonal music, every octave is made of twelve successive notes, often noted:

A A# B C C# D D# E F F# G G#

Or:

La La# Si Do Do# Re Re# Mi Fa Fa# Sol Sol#

In this system, we consider that two successive notes (e.g. A and A#, or E and F) are separated by one semitone. Also, the notes are kind of "looping": what immediately follows G# is A.

A chord is constituted by a few (2, 3, 4, sometimes more) notes that "sound good together". For instance, triadic chords contain three different notes, and seventh chords contain four different notes.

Let's define the four triadic chords as:

• Major triad: contains the root of the chord (in this question, the note given as input), the major third for the root (4 semitones higher than the root), and the perfect fifth for the root (7 semitones higher than the root); this can be symbolized 0-4-7

• Minor triad, symbolized 0-3-7

• Augmented triad, symbolized 0-4-8

• Diminished triad, symbolized 0-3-6

So for example, if you want to make a C major triad, noted C, CM, Cmaj, you will need three noted:

• 0: the root, in this case a C
• 4: the minor third, 4 semitones higher than the root; that's an E
• 7: the perfect fifth, 7 semitones higher than the root: a G

This is what the 0-4-7, 0-3-7, 0-4-8 and 0-3-6 notations used above mean! For the seventh chords, use the following pattern:

That's it for today! Now, amaze me with amazing code... If you have any question, add some comments below.

Answer 1

As you can tell, I didn't try to golf this at all. I'm a music geek, and a pet peeve of mine is when people write things using the wrong enharmonics (e.g. saying that a C diminished chord is C D# F# instead of C Eb Gb), so I wrote this program that gets the enharmonics right. It does so by representing each note as the number of perfect fifths above F.

For what it's worth, if you want to distinguish enharmonics, any musical interval can be represented nicely in a computer program as a number of perfect fifths and a number of octaves. An augmented fourth, for example, is 6 perfect fifths and -3 octaves, and a diminished fifth is -6 perfect fifths and 4 octaves.

Haskell, 441 characters

import Data.List

notes = "FCGDAEB"

fromNum x = [notes !! (mod x 7)] ++ if x < 0 then replicate (-(div x 7)) 'b' else replicate (div x 7) '#'

toNum (x:xs) = y + 7 * if isPrefixOf "b" xs then -length xs else length xs
    where Just y = elemIndex x notes

chord xs = unwords . map (fromNum . \x -> toNum (init xs) + x) $ case last xs of 'A' -> [0,4,8]; 'M' -> [0,4,1]; 'm' -> [0,-3,1]; 'd' -> [0,-3,-6]

main = getLine >>= putStrLn . chord

Some example invocations:

jaspers:junk tswett$ ./chord
AM
A C# E
jaspers:junk tswett$ ./chord
C#m
C# E G#
jaspers:junk tswett$ ./chord
DbA
Db F A
jaspers:junk tswett$ ./chord
Cd
C Eb Gb
jaspers:junk tswett$ ./chord
A#M
A# C## E#
jaspers:junk tswett$ ./chord
Dbm
Db Fb Ab

Answer 2

BBC BASIC

Emulator at bbcbasic.co.uk

Rev 1, 340 - 150 keyboard - 150 playing = 40

Here's the latest version, in which I managed to include the following enhancements while lengthening by only a few more characters.

Input can be edited comfortably on the screen before pressing return (I was using GET$ before to get single keypresses, because BBC Basic does not let you access a single character from a string as if the string was an array. Now I use the rather bulky MID$ function to extract a string of one character from within the string.

Both sides of keyboard displayed as well as the full line between E and F.

To compensate for the characters added by the above, I rearranged the program to eliminate unnecessary print statements, and deleted some white space which at first sight looked like it couldnt be deleted. IN BBC Basic all built in functions are reserved words, and you can put a variable name right before them with no space in between. Variable names are not allowed to start with a reserved word. In order to make the program less confusing to read I changed all variables to lower case.

Although the presentation looks much better, the following program is actually fully golfed already. (See correction below.) Generally newlines and colons are interchangeable, except when an IF statement is used. In that case all statements on the same line (separated by colons) with be executed conditionally. Statements after the newline are not controlled by the IF and will always be executed.

Program rev 1 340 characters

  a$="C#D#EF#G#A#B0Mm+"
  INPUTx$
  r=INSTR(a$,LEFT$(x$,1))-1
  c=INSTR(a$,MID$(x$,2,1))
  IFc=2c=INSTR(a$,MID$(x$,3)):r=r+1
  t=(r+4-c MOD2)MOD12
  f=(r+c DIV2)MOD12
  v=1
  FORn=-1TO11
  c=1-(n<0ORn=4ORn=11)*5
  b$=MID$(a$,n+1,1)
  IFb$="#"c=11:b$=MID$(a$,n,1)+b$
  c$=MID$("   _______--|__",c,5)
  IFr=n ORt=n ORf=n c$=c$+b$:SOUNDv,-15,100+n*4,99:v=v+1
  PRINTc$
  NEXT

CORRECTION: RT Russell's BBC BASIC for Windows allows you to eliminate some newlines and colons, bringing the total down to 327, see below. Also it tokenises the keywords into single characters before saving, bringing it down to 279.

  a$="C#D#EF#G#A#B0Mm+"INPUTx$
  r=INSTR(a$,LEFT$(x$,1))-1c=INSTR(a$,MID$(x$,2,1))IFc=2c=INSTR(a$,MID$(x$,3))r=r+1
  t=(r+4-c MOD2)MOD12f=(r+c DIV2)MOD12v=1FORn=-1TO11c=1-(n<0ORn=4ORn=11)*5b$=MID$(a$,n+1,1)IFb$="#"c=11b$=MID$(a$,n,1)+b$
  c$=MID$("   _______--|__",c,5)IFr=n ORt=n ORf=n c$=c$+b$SOUNDv,-15,100+n*4,99v=v+1
  PRINTc$
  NEXT

Output rev 1

Rev 0, 337 - 150 keyboard - 150 playing = 37

A$="C#D#EF#G#A#B0Mm+":X$=GET$:R=INSTR(A$,X$)-1:X$=GET$:IF X$="#"R=R+1:X$=GET$
C=INSTR(A$,X$):T=(R+4-C MOD2)MOD12:F=(R+C DIV2)MOD12:V=1:PRINT"______"
FORN=0 TO 11
C=1-(N=4)*12:B$=MID$(A$,N+1,1): IF B$="#" C=7: B$=MID$(A$,N,1)+B$
PRINT MID$("    __---|________",C,6);:IF(R-N)*(T-N)*(F-N)=0 PRINT B$;:SOUND V,-15,100+N*4,99:V=V+1
PRINT
NEXT

This is a similar concept to my Arduino answer, but I always knew I could beat that byte count with BBC basic. Only recognises sharps, but considers B# invalid,you must put C. This could be fixed if it was really considered important.

I abandoned the idea of guitar and concentrated on improving the keyboard. It now runs from C to B, and I've added in the left side of the keyboard and the line between E and F. That costs 28 characters. The right hand side wouldn't be much more.

Here's some sample output, an A# diminished chord (which has a pretty freaky sound in this inversion) and a B major chord. Note that the input is not echoed to the screen. As per the Arduino answer, turn the screen anticlockwise to view.

Ungolfed version

A$="C#D#EF#G#A#B0Mm+"                              :REM Note names and chord type names fit very conveniently in the same string.
X$=GET$                                            :REM Get a character 
R=INSTR(A$,X$)-1                                   :REM Root note = position of that char in A$. INSTR starts counting at 1, but we want 0, so subtract.
X$=GET$                                            :REM If the root note is natural, the next character will be the chord type. But...
IF X$="#"R=R+1:X$=GET$                             :REM If this char is # we need to increment the root, and get another char for chord type. 
C=INSTR(A$,X$)                                     :REM C encodes for chord type
T=(R+4-C MOD2)MOD12                                :REM even C means major third, odd C means minor third
F=(R+C DIV2)MOD12                                  :REM "Mm" gives C=14,15 meaning C DIV2=7 (perfect fifth.) C=13,16 give diminished and augmented: 6,8.
V=1                                                :REM V is the sound channel number ("voice")                             
PRINT"______"                                      :REM left side of keyboard for cosmetic reasons
FORN=0 TO 11                                       :REM at the start of each iteration initialise C to 1, to point to the 4 spaces/2 underscores in the string below for drawing white notes. 
  C=1-(N=4)*12                                     :REM if the note is E, add 12 so it points to the 6 underscores to draw the line between E and F. 
  B$=MID$(A$,N+1,1)                                :REM load B$ with the name of the current note.
  IF B$="#" C=7: B$=MID$(A$,N,1)+B$                :REM if the character encountered is a sharp, update C to point the characters for drawing a sharp. Find the previous character in A$ and join it to the beginning of B$ to complete the note name.
  PRINT MID$("    __---|________",C,6);            :REM print the key (6 characters.)
  IF(R-N)*(T-N)*(F-N)=0 PRINT B$;:SOUND V,-15,100+N*4,99:V=V+1  :REM if N is equal to R,T or F, print the note name beside the key, play the note and increment the channel number for the next note.  
  PRINT                                            :REM print a carriage return. It may be possible to golf this line out.
NEXT

Answer 3

Python3 - 315 char

First time in codegolf! Only supports minor, major, diminished and augmented chords right now.

z=["C","C#","D","D#","E","F","F#","G","G#","A","A#","B"];y=[1,2,4,5,6]
def q(a):print(z[a%12])
a=input();k=(ord(a[0])+3)%7;j=k;m=4;s=0;f=7;
for i in y:
    if(k>=i):j+=1
if('#'in a):j+=1
if('b'in a):j-=1
if('m'in a or'0'in a):m=3
if('+'in a or"aug"in a):f=8
if('0'in a or"dim"in a):f=6;m=3
if('ma'in a):m=4
q(j);q(j+m);q(j+f);

Answer 4

Arduino

Input/output is sent to / received from the Arduino via a COM port. A user can interact with this via a terminal, or the serial monitor in the Arduino IDE. As you may have guessed from my choice of platform, I am planning to include the actual playing of the chord (though I haven't done it yet.)

I have tackled the keyboard bonus successfully, and I have tried to tackle the guitar, with limited success.

The chord box comes in at 130 bytes, which is too long to be worth it. Therefore I have tried another way, just printing the fret numbers Tab style. Currently this is 81 bytes for a bonus of 81-100=-19. If this approach is deemed valid I can try and improve on it.

The chords used are all D-type shapes with the root on the 2nd string, fifth on the 3rd string, and third on the 1st and 4th strings. The 5th and 6th strings are not used and I mark this with X's on the right of the chord box (the left would be more usual, but examples marked on the right can be found.)

Because the program considers F to be the lowest note (for compatability with the keyboard while avoiding excessively high frets with this chord shape) the highest chord is an E (with root on the 17th fret.) See example output.

The keyboard is more successful in terms of golfing. It runs from F-E rather than C-B for the reasons described above. It must be viewed by turning the screen 90% anticlockwise, when you can clearly see the outlines of the black notes, and the demarcation between the white notes with ---. The line between B an C could be extended with some ____ for a few more bytes.

I will try playing the notes next. This will be interesting because, although I believe the Arduino Uno has 3 internal timers, only one note at a time can be played using the built in tone command. There is an external library function which uses all the hardware timers (which will mess up the serial, but it won't be needed at that stage anyway.) Alternatively I may try to produce the tones in softare.

If I am successful with that, I will golf it down but I don't think it will be the overall winner.

Ungolfed code

String p="F#G#A#BC#D#E -Mm+",y,d[]=
{"    ","---|"},n="\n";

void setup() {
  Serial.begin(9600);
  Serial.setTimeout(99999);
}

void loop(){
  char x[9]; int r,t,f,i,c=1;
  Serial.readBytesUntil(13,x,9);
  Serial.println(x);  
  r=p.indexOf(x[0]);
  if (x[1]==35|x[1]==98){c=2;r+=x[1]==35?1:-1;}
  f=p.indexOf(x[c])/2;
  t=4-p.indexOf(x[c])%2;

  //chord box
  y=n;for(i=24;i--;)y+=d[1]+(i%4?"":" \n");
  y[89]=y[107]='X'; y[t*4-10]=y[t*4+52]=y[f*4+14]=y[28]='O';
  Serial.print("\t "+String(r+6)+y);
  
  f+=r;t+=r;

  //tab style
  Serial.println(String(t+1)+n+String(r+6)+n
  +String(f-2)+n+String(t+3)+"\nX\nX\n");
  
  f%=12;t%=12;

  //piano
  for(i=0;i<12;i++){
    c=0;
    y=String(p[i]);
    if(y=="#") {c=1;y=p[i-1]+y;}      
    Serial.println(d[c]+"__"+((r-i&&t-i&&f-i)?"":y));
  }  
}

Sample output The lower the spacing between the lines of text, the better this looks. Therefore it looks great when I am actually editing the post, but horrible in the grey box after posting. Instead I've posted a screenshot of the Arduino serial monitor which is of intermediate line spacing (and hence display quality.)

Answer 5

Python 506(unicode as 1 char)-150(sound)-150(keyboard) = 206

For sound playing, it uses pygame.midi. Note that the pygame.midi.get_default_output_id() method don't work very well. So you may try changing the line o=Output(get_default_output_id()) to o=Output(1), o=Output(2), etc. Usually the correct value is between 0 and 5.

c=input()
s='C D EF G A B'.index(c[0])+{'#':1,'b':-1,'':0}[c[1:-1]]
m='0mM+'.index(c[-1])
t=s+3+m//2
R=[list(x)for x in['┌─'+'─┬─'*13+'─┐']+['│'+'  │'*14]*5+['└─'+'─┴─'*13+'─┘']]
i=3
for d in[3,6,3,3,6]*2:q=slice(i-1,i+2);R[0][q]='┬─┬';R[1][q]=R[2][q]=R[3][q]='│ │';R[4][q]='└┬┘';i+=d
X=[2]+[1,2,1,2,3,1,2,1,2,1,2,3]*2
from pygame.midi import*
init()
o=Output(get_default_output_id())
for s in[s,t,t+3+m%2]:R[[5,3][s%12 in[1,3,6,8,10]]][sum(X[:s+1])]='o';o.note_on(s+60,127,1)
for r in R:print(''.join(r))

Results

goooolf> python chords2.py
CM
┌─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┬─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┐
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │
│ o│  │ o│  │ o│  │  │  │  │  │  │  │  │  │
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
goooolf> python chords2.py
Cm
┌─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┬─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┐
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││o│ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │
│ o│  │  │  │ o│  │  │  │  │  │  │  │  │  │
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
goooolf> python chords2.py
Dm
┌─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┬─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┐
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │
│  │ o│  │ o│  │ o│  │  │  │  │  │  │  │  │
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
goooolf> python chords2.py
D+
┌─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┬─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┐
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │o││ ││o│ │ │ ││ │ │ │ ││ ││ │ │
│ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │
│  │ o│  │  │  │  │  │  │  │  │  │  │  │  │
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
G+
┌─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┬─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┐
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││o│ │ │ ││ ││ │ │
│ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │
│  │  │  │  │ o│  │ o│  │  │  │  │  │  │  │
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
goooolf> python chords2.py
Am
┌─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┬─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┐
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │
│  │  │  │  │  │ o│  │ o│  │ o│  │  │  │  │
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
goooolf> python chords2.py
C#0
┌─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┬─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┐
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │o││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │
│  │  │ o│  │ o│  │  │  │  │  │  │  │  │  │
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
goooolf> python chords2.py
EbM
┌─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┬─┬─┬┬─┬─┬─┬─┬┬─┬┬─┬─┐
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││ │ │ │ ││ ││ │ │ │ ││ │ │ │ ││ ││ │ │
│ │ ││o│ │ │ ││ ││o│ │ │ ││ │ │ │ ││ ││ │ │
│ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │ └┬┘└┬┘ │ └┬┘└┬┘└┬┘ │
│  │  │  │  │ o│  │  │  │  │  │  │  │  │  │
└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘

Answer 6

J - 82 char

Self-contained, reads from console input. If you need stdin, change the final 1 to a 3. Claiming no bonuses, and only covering the triads.

+/&(0 3 6++/\_3{.#:'0mM+'i.{:e)&.((,~C`Db`D`Eb`E`F`Gb`G`Ab`A`Bb`B)i.;:)}:e=.1!:1]1

Instead of a sharp note e.g. C# you must use the equivalent flat name Db. (Correcting for this would inflate the code by more than a bit.) The four types of chords are 0 for diminishing, m for minor, M for major, and + for augmented.

The logic is as follows: we use the last character to add an offset to the base 0-3-6, which selects the kind of third and fifth. Meanwhile, we use the note to find where in the scale to pull the notes from. The ;: both makes the note compatible with indexing into the scale at the start, and later (by &.) turns the pulled notes into a space separated string.

Example usage:

   +/&(0 3 6++/\_3{.#:'0mM+'i.{:e)&.((,~C`Db`D`Eb`E`F`Gb`G`Ab`A`Bb`B)i.;:)}:e=.1!:1]1
AM
A Ch E
   +/&(0 3 6++/\_3{.#:'0mM+'i.{:e)&.((,~C`Db`D`Eb`E`F`Gb`G`Ab`A`Bb`B)i.;:)}:e=.1!:1]1
Ab0
Ab B D
   +/&(0 3 6++/\_3{.#:'0mM+'i.{:e)&.((,~C`Db`D`Eb`E`F`Gb`G`Ab`A`Bb`B)i.;:)}:e=.1!:1]1
B+
B Eb G
   +/&(0 3 6++/\_3{.#:'0mM+'i.{:e)&.((,~C`Db`D`Eb`E`F`Gb`G`Ab`A`Bb`B)i.;:)}:e=.1!:1]1
Em
E G B

Answer 7

Javascript, 224 char

n=prompt();a="A0A#0B0C0C#0D0D#0E0F0F#0G0G#".split(0);x=1;r=a.indexOf(n[0]);n[1]=="#"&&(r++,x++);n[1]=="b"&&(r--,x++);s=r+4;l=r+7;(n[x]=="m"||n[x]==0)&&s++;s%=12;n[x]=="+"&&l++;n[x]==0&&l--;l%=12;alert(a[r]+" "+a[s]+" "+a[l])

This is my first code golf. I think it can be shorter, but I can't find any bytes to save.

Supports major, m for minor, 0 for diminished, + for augmented, or 37 more bytes for dim, aug.

Answer 8

Python (143 134 chars)

n,a='A A# B C C# D D# E F F# G G#'.split(),input();m,i=ord(a[-1])-42,n.index(a[:-1])
print(n[i],n[(i+4-m//2)%12],n[(i-4+(-m//2))%12]) 

My first golf challenge :), don't know if some more bytes can be shaved off.
The notation used here is * aug / + maj / , min / - dim
I deserve a bonus point for having the constant 42 in the code :P

Answer 9

Scala 537 chars - 50

import java.util.Scanner
object C extends App{
val c=Map("M"->145,"m"->137,"+"->273,"0"->73,"7"->1169,"M7"->2193,"m7"->1161,"Mm7"->2185,"+7"->1297,"+M7"->2321,"07"->585,"7b5"->1097)
val n=List("A","A#","B","C","C#","D","D#","E","F","F#","G","G#")
val o=List("","Bb","Cb","B#","Db","","Eb","Fb","E#","Gb","","Ab")
val s=new Scanner(System.in).nextLine
val v=s indexWhere{c=>c!='#'&&c!='b'&&(c<'A'||c>'G')}
val (u,m)=s splitAt v
val x=n.indexOf(u)max o.indexOf(u)
val k=c(m)
for(i<-0 to 11)if((k&(1<<i))!=0)print(n((i+x)%12)+" ")
println}

Answer 10

Python 3: 257 - 150 = 107

Just 25 chars too long to beat the J solution! Oh well. There are some neat ideas here, I think.

I='AaBCcDdEFfGg'*2
Q='0123456789.,'*2
K="""-1#_2
-,#_0
-9#_.
____8
-6#_7
-4#_5
____3"""
r,*R,q=input()
r=I.find(r)+bool(R)
p=str.replace
for x in[0]+[8,4,7,3,6]['+Mm0'.find(q):][:2]:K=p(K,Q[x+r],I[x+r].upper())
for x in Q:K=p(K,x,' ')
print(p(K,' #','  '))

Input is like the examples, though you must use sharp names instead of flat names. (e.g. Gb must be F#)

Output is a single octave of a piano, seen from above and to the left, with note names superimposed. Should be just a tiny stretch of the imagination.

$ echo C#m | python3 chords.py
-  _ 
-G#_ 
-  _ 
____ 
-  _E
-C#_ 
____ 

Answer 11

Raku, 216 bytes

Shorter than my original Scala solution and spells pitches correctly to boot.

for $*IN.lines {m:P5/([A-G])(\#*)(b*)([Mm+0])/;my \r=4613502.comb[$0.ord-65]+7*($1.comb-$2.comb);put %(:M<0 4 1>,:m<0 -3 1>,"+",<0 4 8>,0,<0 -3 -6>){$3}.map({"FCGDAEB".comb[($/=r+$_)%7]~(<b #>)[$/>0]x abs($/div 7)})}

Try it online!

Answer 12

Haskell, 273 chars

n(s,a)="CCDDEFFGGAABB"!!(s+1-a):["b#"!!a|" b b  b b b "!!s/=' ']
t p=[(s,a)|s<-[11,10..0],a<-[0,1],n(s,a)==p]!!0
m(s,d)=n(mod s 12,d-3)
c q=[n(a,x),m(a+d,d),m(a+d+e,e)]where
 (a,x)=t$init q;f=lookup(last q).zip"0mM+";Just d=f[3,3,4,4];Just e=f[3,4,3,4]
main=print.c=<<getLine

Results

C0 ->["C","Eb","Gb"]   Cm ->["C","Eb","G"]    CM ->["C","E","G"]     C+ ->["C","E","G#"]    
C#0->["C#","F","G"]    C#m->["C#","F","G#"]   C#M->["C#","F","Ab"]   C#+->["C#","F","A"]    
D0 ->["D","F","Ab"]    Dm ->["D","F","A"]     DM ->["D","F#","A"]    D+ ->["D","F#","A#"]   
D#0->["D#","Gb","A"]   D#m->["D#","Gb","A#"]  D#M->["D#","G","Bb"]   D#+->["D#","G","B"]    
E0 ->["E","G","Bb"]    Em ->["E","G","B"]     EM ->["E","G#","B"]    E+ ->["E","G#","C"]    
F0 ->["F","Ab","B"]    Fm ->["F","Ab","C"]    FM ->["F","A","C"]     F+ ->["F","A","C#"]    
F#0->["F#","A","C"]    F#m->["F#","A","C#"]   F#M->["F#","A#","Db"]  F#+->["F#","A#","D"]   
G0 ->["G","Bb","Db"]   Gm ->["G","Bb","D"]    GM ->["G","B","D"]     G+ ->["G","B","D#"]    
G#0->["G#","B","D"]    G#m->["G#","B","D#"]   G#M->["G#","C","Eb"]   G#+->["G#","C","E"]    
A0 ->["A","C","Eb"]    Am ->["A","C","E"]     AM ->["A","C#","F"]    A+ ->["A","C#","F"]    
A#0->["A#","Db","F"]   A#m->["A#","Db","F"]   A#M->["A#","D","F"]    A#+->["A#","D","F#"]   
B0 ->["B","D","F"]     Bm ->["B","D","F#"]    BM ->["B","D#","Gb"]   B+ ->["B","D#","G"]