Permalink
Switch branches/tags
Nothing to show
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
728 lines (529 sloc) 21 KB

Basic types

Let's look at the basic types of the library.

Signals (Sig)

We are going to make an audio signal. So the most frequently used type is a signal. It's called Sig. The signal is a stream of numbers that is updated at a certain rate. Actually it's a stream of small arrays of doubles. For every cycle the audio-engine updates it. It can see only one frame at the given time.

Conceptually we can think that signal is a list of numbers. A signal is an instance of type class Num, Fractional and Floating. So we can treat signals like numbers. We can create them with numeric constants, add them, multiply, subtract, divide, process with trigonometric functions.

We assume that we are in ghci session and the module Csound.Base is loaded.

$ ghci
> import Csound.Base

So let's create a couple of signals:

> x = 1 :: Sig
> y = 2 :: Sig
> z = (x + y) * 0.5

In the older versions of ghci we need to write let in the interpreter to delcalre a variable or function in modern versions it can be omitted. So if it's not working for you, just include let keyword like this:

> let x = 1 :: Sig

Constants are pretty good but not that interesting as sounds. The sound is time varying signal. It should vary between -1 and 1. It's assumed that 1 is a maximum volume. Everything beyond the 1 is clipped.

Let's study the simple waveforms:

osc, saw, tri, sqr :: Sig -> Sig

They produce sine, sawtooth, triangle and square waves. The output is band limited (no aliasing beyond Nyquist). The waveform function takes in a frequency (and it's also a signal) and produces a signal that contains wave of certain shape that is repeated with given frequency (in Hz).

Let's hear a sound of the triangle wave at the rated of 220 Hz:

> dac $ tri 220

We can press Ctrl+C to stop the sound from playing. If we know the time in advance we can set it with the function setDur:

> dac $ setDur 2 $ tri 220

Right now the sound plays only for 2 seconds. The setDur function should be used only once. Right before the sending output to the dac. Please don't use it many times for example to set duation of notes, it's only for setting total duration of the whole track.

We can vary the frequency with slowly moving oscillator:

> dac $ tri (220 + 100 * osc 0.5)

If we use the saw in place of tri we can get a more harsh siren-like sound.

We can adjust the volume of the sound by multiplying it:

> dac $ mul 0.5 $ saw (220 + 100 * osc 0.5)

Here we used the special function mul. We could just use the normal Haskell's *. But mul is more convenient. It can work not only for signals but for tuples of signals (if we want a stereo playback) or signals that contain side effects (wrapped in the monad SE). So the mul is preferable.

Constant numbers (D)

Let's study two another useful functions:

leg, xeg :: D -> D -> D -> D -> Sig

They are Linear and eXponential Envelope Generators. They create ADSR-envelopes.

They take in a four arguments. They are:

  • attack time: time for signal to reach the 1 (in seconds)

  • decay time: time for signal to reach the sustain level (in seconds)

  • sustain level: the value for sustain level (between 0 and 1)

  • release time: how many seconds it takes to reach the zero after release.

We can notice the new type D in the signature. It's for constant doubles. We can think that it's a normal value of type Double. It's a Double that is embedded in the Csound. From the point of implementation we don't calculate these doubles but use them to generate the Csound code.

Let's create a signal that is gradually changes it's pitch:

> dac $ saw (50 + 150 * leg 2 2 0.5 1)

Notice that signal doesn't reaches the release phase. It's not a mistake! The release happens when we release a key on the midi keyboard. We don't use any midi here so the release never happens.

But we can try the virtual midi device:

> vdac $ midi $ onMsg $ \x -> saw (x + 150 * leg 2 2 0.5 1)

Right now don't bother about the functions midi and onMsg. We are going to take a closer look at then in the chapter User interaction. That's how we plug in the midi-devices.

The value of type D is just like a Haskell's Double. We can do all the Double's operations on it. It's useful to know how to convert doubles to D's and how to convert D's to signals:

double :: Double -> D
int    :: Int    -> D
sig    :: D      -> Sig

There are more generic functions:

linseg, expseg :: [D] -> Sig

They can construct the piecewise linear or exponential functions. The arguments are:

linseg [a, timeAB, b, timeBC, c, timeCD, d, ...]

They are alternating values and time stamps to progress continuously from one value to another. Values for expseg should be positive (above 0 and not 0).

There are two more generic functions for midi notes:

linsegr, expsegr :: [D] -> D -> D -> Sig

The two last arguments are the release time and the final value for release stage. They are usefull for midi-instruments.

Another frequently used functions are

fadeIn  :: D -> Sig
fadeOut :: D -> Sig

fades   :: D -> D -> Sig
fades fadeInTime fadeOutTime = ...

They produce more simple envelopes. The fadeIn rises in the given amount of seconds form 0 to 1. The fadeOut does the opposite. It's 1 from the start and then it fades out to zero in given amount of seconds but only after release. The fades combines both functions.

Strings (Str)

The friend of mine has made a wonderful track in Ableton. I have a wav-file from her and want to beep-along with it. I can use a diskin2 opcode for it:

diskin2 :: Tuple a => Str -> a
diskin2 fileName = ...

It takes in a name of the file and produces a tuple of signals. We should specify how many outputs are in the record by specifying precise the type of the tuple. There are handy helpers for this:

ar1 :: Sig -> Sig
ar2 :: (Sig, Sig) -> (Sig, Sig)
ar3 :: (Sig, Sig, Sig) -> (Sig, Sig, Sig)
ar4 :: (Sig, Sig, Sig, Sig) -> (Sig, Sig, Sig, Sig)

Every function is an identity. It's here only to help the type inference. Let's say we have a file Noise.wav. With a mono wav-file we can use:

> sample = ar1 $ diskin2 (text "Noise.wav")

The first argument of the diskin2 is not a Haskell's String. It's a Csound's string so it has a special name Str. It's just like D's for Double's. We used a converter function to lift the Haskell string to Csound one:

text :: String -> Str

The function text converts the Haskell strings to Csound ones. The Str has instance of IsString so if we are using the extension OverloadedStrings we don't need to call the function text.

For a stereo wav file "Composite.wav" we use:

> :set -XOverloadedStrings
> sample = toMono $ ar2 $ diskin2 "Composite.wav"

We don't care right now about the stereo so we have converted everything to mono with function.

toMono :: (Sig, Sig) -> Sig

Ok, we are ready to play along with it:

> sample = toMono $ ar2 $ diskin2 (text "Composite.wav")
> meOnKeys = midi $ onMsg osc
> vdac $ mul 0.5 $ meOnKeys + pure sample

Notice how simple is the combining midi-devices output with the regular signals. The function midi produces a normal signal wrapped in SE-monad. We can use it anywhere. We use standard function pure to wrap ordinary value to SE-type. We do it so that types of values meOnKeys and sample match to each other and we can sum them up.

There are useful shortcuts that let us use a normal Haskell strings:

readSnd :: String -> (Sig, Sig)
loopSnd :: String -> (Sig, Sig)
loopSndBy :: D -> String -> (Sig, Sig)
readWav :: Sig -> String -> (Sig, Sig)
loopWav :: Sig -> String -> (Sig, Sig)

The functions with read play the sound files only once. The functions with loop repeat over the sample over and over. With loopSndBy we can specify the time length of the loop period. The readWav and loopWav can read the file with given speed. The 1 is a normal speed. The -1 is playing in reverse. Negative speed works only for loopWav.

So we can read our friends record like this:

sample = loopSnd "Composite.wav"

If we want only a portion of the sound to be played we can use the function:

takeSnd :: Sigs a => Sig -> a -> a

It takes only given amount of seconds from the input signal and fills the rest with silence.

The first argument is signal, but often it's set with a constant or it's taken from signal on the moment of invocation (it's like a constant snapshot). the second type is a bit unusual: Sigs a => a. In Haskell notation it means anything which is signal-like. It means not only a signal but all sorts of tuples of signals. It's useful so that we can use the same function with mono and stereo or Dolby-surround audio signals.

It's interesting that we can loop not only with samples but with regular signals too:

repeatSnd :: Sigs a => Sig -> a -> a

It loops the signal over given amount of time (in seconds). We can try it out:

> dac $ repeatSnd 3 $ leg 1 2 0 0 * osc 220

Tables (Tab)

We have studied the four main waveform functions: osc, tri, saw, sqr. But what if we want to create our own waveform. How can we do it?

What if we want not a pure sine but two more partials. We want a sum of sine partials and a first harmonic with the amplitude of 1 the second is with 0.5 and the third is with 0.125.

We can do it with osc:

> wave x = mul (1/3) $ osc x + 0.5 * osc (2 * x) + 0.125 * osc (3 * x)
> vdac $ midi $ onMsg $ mul (fades 0.1 0.5) . wave

But there is a better way for doing it. Actually the oscillator reads a table with a fixed waveform. It reads it with a given frequency and we can hear it as a pitch. Right now our function contains three osc. Each of them reads the same table. But the speed of reading is different. It would be much better if we could write the static waveform with three harmonics in it and read it with one oscillator. It would be much more efficient. Think about waveforms with more partials.

We can achieve this with function:

oscBy :: Tab -> Sig -> Sig

It creates an oscillator with a custom waveform. The static waveform is encoded with value of type Tab. The Tab is for one dimensional table of doubles. In the Csound they are called functional tables. They can be created with GEN-routines. We don't need to create the tables directly. Like filling each cell with a value (going through the table in the loop). There are plenty of functions that can create specific tables.

Right now we want to create a sum of partials or harmonic series. We can use the function sines:

sines :: [Double] -> Tab

Let's rewrite the example:

> wave x = oscBy (sines [1, 0.5, 0.125]) x
> vdac $ midi $ onMsg $ mul (fades 0.1 0.5) . wave

You can appreciate the simplicity of these expressions if you try to make it directly in the Csound. But you don't need to! There are better ways and here is one of them.

What if we want not 1, 2, and third partials but 1, 3, 7 and 11? We can use the function:

sines2 :: [(PartialNumber, PartialStrength)] -> Tab

It works like this:

> wave x = oscBy (sines2 [(1, 1), (3, 0.5), (7, 0.125), (11, 0.1)]) x

The table size

What is the size of the table? We can create the table of the given size. By default it's 8196. The more size the better is precision. For efficiency reason the tables size in most cases should be equal to some degree of 2. We can set the table size with one of the functions:

lllofi, llofi, lofi, midfi, hifi, hhifi, hhhifi :: Tab -> Tab

The lllofi is the lowest fidelity and the hhhfi is the highest fidelity.

We can set the size explicitly with:

setSize :: Int -> Tab -> Tab

In many cases the table size should be the power of two, consult the corresponding docs for Csound reference manual (see the section on GEN-routines).

The guard point

If you are not familiar with Csound's conventions you are probably not aware of the fact that for efficiency reasons Csound requires that table size is equal to power of 2 or power of two plus one which stands for guard point (you do need guard point if your intention is to read the table once but you don't need the guard point if you read the table in many cycles, then the guard point is the the first point of your table).

If we read the table once we have to set the guard point with function:

guardPoint :: Tab -> Tab

There is a short-cut called just gp. We should use it with exps or lins.

Specific tables

There are a lot of GEN-routines available. Let's briefly discuss the most useful ones.

We can write the specific numbers in the table if we want:

doubles :: [Double] -> Tab

Linear and exponential segments:

consts, lins, exps, cubes, splines :: [Double] -> Tab

Reads samples from files (the second argument is duration of an audio segment in seconds)

data WavChn = WavLeft | WavRight | WavAll
data Mp3Chn = Mp3Mono | Mp3Stereo | Mp3Left | Mp3Right | Mp3All

wavs :: String -> Double -> WavChn -> Tab
mp3s :: String -> Double -> Mp3Chn

Harmonic series:

type PartialStrength = Double
type PartialNumber   = Double
type PartialPhase    = Double
type PartialDC       = Double

sines  :: [PartialStrength] -> Tab
sines2 :: [(PartialNumber, PartialStrength)] -> Tab
sines3 :: [(PartialNumber, PartialStrength, PartialPhase)] -> Tab
sines4 :: [(PartialNumber, PartialStrength, PartialPhase, PartialDC)] -> Tab

Special cases for harmonic series:

sine, cosine, sigmoid :: Tab

There are other tables. We can find the complete list in the module Csound.Tab. In Csound the tables are created by specific integer identifiers but in CE they are defined with names (hopefully self-descriptive). If you are used to integer identifiers you can check out the names in the Appendix to the documentation of the Csound.Tab module.

Side effects (SE)

The SE-type is for functions that work with side effects. They can produce effectful value or can be used just for the side effect.

For example every function that generates random numbers uses the type SE.

To get the white, pink or red (Brownian) noise we can use:

white :: SE Sig
pink  :: SE Sig
brown :: SE Sig

Let's listen to the white noise:

> dac $ mul 0.5 $ white

We can get the random numbers with linear interpolation. The output values lie in the range of -1 to 1:

rndi :: Sig -> SE Sig

The first argument is frequency of generated random numbers. We can get the constant random numbers (it's like sample and hold function with random numbers):

rndh :: Sig -> SE Sig

We can use the random number generators as LFO. The SE is a Functor, Applicative and Monad. Those are standard ways to manipulate values that are wrapped in some sort of behaviour or are containers. We rely on these properties to get the output.

With Functor we can map over wrapped value:

> instr lfo = 0.5 * saw (440 + lfo)
> dac $ mul 0.5 $ fmap instr (20 * rndi 5)

We use function fmap:

fmap :: Functor f => (a -> b) -> f a -> f b

There are unipolar variants: urndh and urndi. The output ranges form 0 to 1 for them.

Note that the function dac can work not only signals but also on the signals that are wrapped in the type SE and also on all sorts signal-like or renderable values.

Let's take a break and listen to the filtered pink noise:

> dac $ mul 0.5 $ fmap (mlp (on 50 2500 $ tri 0.2) 0.3) $ pink

The function on is useful for mapping the range (-1, 1) to a different interval. In the expression on 50 2500 $ tri 0.2 oscillation happens in the range (50, 2500). There is another useful function uon. It's like on but it maps from the range (0, 1).

The essence of the SE Sig type lies in the usage of random values. In the pure code we can not distinguish between these two expressions:

x1 =
  let a = rndh 1
  in a + a

x2 = rndh 1 + rndh 1

For x1 we want only one random value but for x2 we want two random values.

The value is just a tiny piece of code (we don't evaluate expressions but use them to generate Csound code). The renderer performs common subexpression elimination. So the examples above would be rendered in the same code.

We need to tell to the renderer when we want two random values. Here comes the SE monad (Side Effects for short).

x1 = do
  a <- rndh 1
  return $ a + a

x2 = do
  a1 <- rndh 1
  a2 <- rndh 1
  return $ a1 + a2

The SE was introduced to express the randomness. But then it was useful to express many other things. Procedures for instance. They don't produce signals but do something useful:

procedure :: SE ()

The SE is used for allocation of delay buffers in the functions.

deltap3 :: Sig -> SE Sig
delayr :: D -> SE Sig
delayw :: Sig -> SE ()

The deltap3 is used to allocate the delay line. After allocation we can read and write to delay lines with delayr and delayw.

The SE is used for allocation of local or global variables (see the type SERef in the module Csound.Control.SE).

For convenience the SE Sig and SE of tuples of signals is instance of Num. We can sum and multiply the signals wrapped in the SE. The code is ok:

> dac $ white + 0.5 * pink
> dac $ white + return (osc 440)

Mutable values

We can create mutable variables. It works just like the normal Haskell mutable variables. We can create a reference and the we should use the functions on the reference to read and write values.

There are two types of the variables: local and global variables. The local variables are visible only within one Csound instrument. The global variables are visible everywhere.

We can create a reference to the mutable variable with functions:

newRef          :: Tuple a => a -> SE (Ref a)
newGlobalRef    :: Tuple a => a -> SE (Ref a)

They take in an initial value and create a value of the type Ref:

data Ref a = Ref
	{ writeRef :: a -> SE ()
	, readRef  :: SE a
	}

We can write and read values from reference.

Mutable values with control signals

By default newRef or newGlobalRef create placeholders for audio-rate signals. But if we want them to hold control-rate signals we have to use special variants:

newCtrlRef          :: Tuple a => a -> SE (Ref a)
newGlobalCtrlRef    :: Tuple a => a -> SE (Ref a)

If signals are created with them they are control-rate signals.

Tuples (Tuple)

Some of the Csound functions are producing several outputs. Then the output is represented with Tuple. It's a special type class that contains all tuples of Csound values.

There is a special case. The type Unit. It's Csound's alias for Haskell's ()-type. It's here for implementation reasons.

We have already encountered the tuples when we have studied the function diskin2.

diskin2 :: Tuple a => Str -> a

In Csound the functions can produce varied amount of arguments. The number of arguments is specified right in the code. But Haskell is different. The function can produce only certain number of arguments. To relax this rule we can use the special type class Tuples. Now we can return different number of arguments. But we have to specify them with type signature. There are helpers to make it easier:

ar1 :: Sig -> Sig
ar2 :: (Sig, Sig) -> (Sig, Sig)
ar3 :: (Sig, Sig, Sig) -> (Sig, Sig, Sig)
ar4 :: (Sig, Sig, Sig, Sig) -> (Sig, Sig, Sig, Sig)

Also we can just specify the type of output:

In the interpreter:

> sample = diskin2 (text "fox.wav") :: Sig2
> :t sample
 sample :: Sig2

Or in the code:

sample :: Sig2
sample = diskin2 (text "fox.wav")