What's it like not having synaesthesia?
That sounds like a flippant answer, but it's quite the truth. I can't remember a time when I didn't experience sounds (music, in particular) in a deep, visceral way that involved more than just my sense of hearing. For the longest time I thought everybody's experience of life was like mine. I thought everybody cried when they heard violin music. I thought everybody felt waves of cold and prickles when they heard sounds made up of square waves (yeah, I'm dating myself, aren't I?) Didn't everybody shiver and see starbursts of pink and purple light when they heard a particular chord progression on the radio (strangely, the original Also Sprach Zarathustra doesn't have that effect on me - must be the pedals Andy Summers used in the studio)? Didn't everybody feel... pain... when they just heard something shrieking or screaming, like bus brakes or the scream of a dentist's drill (note: video of actual drill-and-fill; feel free to not click on it)?
To answer my (rhetorical) question another way, everybody seems to be synaesthetic to some degree. Take a look at this image.
Now, tell me: Of what you see in that image file, which one is Kiki and which one is Bouba?
If you said that the spiky one was Kiki and the round blobby one was Bouba, you're not alone. Between 95% and 98% of people asked that same question say the same thing. Which goes to show that having a cross-wired sensorium probably isn't that unusual a phenomenon when you think about it. It seems that synaesthesia is more pronounced in some and less in others, per the bell curve distribution (yes, that page is pimping somebody's service; it's the best I could find without some hardcore digging).
To some extent, synaesthetic perception seems to be conditioned. The tendency toward conflation is there in the neural networks but it seems partially unformatted at first. This strongly implies that the kind of synaesthesia one can have may manifest in a fashion that mimics common sensory stimuli in the environment. For example, the author Vladimir Nabokov (as well as his mother and son) described having grapheme-color synaesthesia: They perceived letters as being associated with colors to a strikingly consistent degree with each other. Interestingly, the correlations were substantially the same as those of a very common set of children's building blocks that depict letters and numbers, which seems to imply that their brains, which were already configured for a tendency toward synaesthesia imprinted upon those early patterns. For me, I grew up hacking around on my Commodore 64, which didn't have the kind of graphics we take for granted today, as well as listening to (probably) way too many chiptunes. I suspect this is the reason that the visual distortions I see are mostly patterns of pixellation. Somebody with different formative experiences would undoubtedly experience different things.
It also seems somewhat common for synaesthetes to have multiple sensory modalities involved, all tied to a primary sense. This is to say that more than one sense is manipulated in response to a single stimulus. For example, Geoffrey Rush experiences grapheme-color (letters to colors) and spatio-temporal (times and dates manifest as phantom locations) synesthetic modalities. Billy Joel has talked about experiencing notes, music, and letters as having distinct color schemes. (source) There are forms of synaesthesia which are even more unusual. Stevie Wonder, who's been blind almost his entire life, perceives music as colors. There are deaf people who perceive colors in response to sign language. Tilda Swinton perceives words as having associations with food.
Personally, I primarily see patterns of colors in response to things I hear. Lyssa's Voice looks like shimmering plaids made up of shades of green and blue. My mother's voice always looks like there are patterns of yellow and grey sand on top of everything. Laurelindel's voice seems like amoeba-like patterns in different shades of green. Depending on the sound (or patterns of sound), my senses of touch, proprioception, and emotions may additionally be involved, and they're don't always match up with what the sound is. My mother's voice also has a feeling of warm pressure on the base of my skull, where it meets the C-spine. There are one or two singers whose voices are such that listening to them evokes the sensation of my chest vibrating, like when you sing in the tenor vocal range and you open up and really, really nail a G4 or A5; depending on the voice I might also feel a sensation of heat on my ribs. The aforementioned shriek of brake dust on a bus, or someone singing notes up in the whistle register (I'm not going to call her out because she hasn't done anything wrong) warps my perception of my body such that I feel like I have an extra pair of legs connected to my hips, and then somebody starts yanking them apart. It's incredibly painful.
It's fucked up, too. Nothing in life is all chocolate and strawberries.
So.. what do I get out of music, really?
I'm no artist, but maybe this'll come close.
Give this a listen - Reich mir die Hand by Blutengel (there's some NSFW content in the video, so open it in another browser tab). The tolling of the churchbell makes the lower edge of my vision quiver. When the keyboard kicks in (the one set up with violin samples) it feels like my fingers are moving. I studied the piano for a while in undergrad, so I've got some amount of fingering technique programmed into my reflex arc and cerebellum, and what I hear seems to trigger those movements. Years before I studied the alto and tenor saxophone, and the sensations almost (but not quite) mimicked left hand and right hand fingerings. Before that... you guessed it, it felt like I was typing on a keyboard with oversized keys and a heavy stroke. The C-64 again. A sensation of tightness, not unlike a clenched fist rises and falls in my C- and T- spine, following the positions on the scale the notes of the melody follow. Oscillating bars of yellow and white cut across the center of my vision, tracking Chris Pohl's baritone voice.
Now give this a shot - Saving Time by Iris. An oldie but goodie.
Orange circles of light explode in the left half of my vision as the keyboards really start the melody and back Reagan Jones' vocals. Pretty waves, like looking out over the ocean seem to underlie everything, in time with the arpeggiator that fills in most of the background of the song. It's like watching the ocean against a stiff breeze. Reagan's voice presses on my chest and the roof of my mouth; it's oddly inspiring, in a way. Saving Time was always one of my favorite songs to sing on long road trips, because it let me do something with the phantom pressure I feel. At the very end, when the electric guitar finally makes an appearance, it seems as if my arms start moving, tracing the chord progression in the air. They're sitting on the keyboard while I try to come up with words to describe the sensation, but fucked if I don't feel like they're following the notes on an invisible scale passing from as far as my right arm can reach through my left shoulder.
A reasonable question to ask might be, does my synaesthesia control me, or do I control it? The answer is, I'm in control of my actions. While my senses don't seem to work like everybody else's, they don't drag me around by the nose. I made it 28 years more-or-less okay; I'm successful and functional in everyday life and neither my parents, in-laws, family, or cow-orkers have LARTed me (yet). Is it crippling? no. Why would it be? I don't remember a time when I didn't experience the world this way, so it's never held me back any. Aside from the odd bit of phantom pain, but that's beside the point. While everyone has a different experience of the world through the course of their lives, I get something perhaps unusual and not particularly detrimental out of it. No moreso than anyone else, I should think.