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Programming language: Haskell
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Csound-expression guide

Join the chat at https://gitter.im/anton-k/csound-expression

Welcome to the simplest textual synthesizer.

> dac $ osc 440

Csound-expression is a Haskell framework for computer music. With the help of the library we can create our instruments on the fly. A couple of lines in the interpreter is enough to get the cool sound going out of your speakers. It can be used for simple daily sound-file processing or for a full-blown live performances. It's available on Hackage.

Let's look at how we can create computer music with Haskell.


WARNING: the library works best within ghci. The real-time sound rendering function dac spawns a child process in the background which may continue to execute after you stop the main process that runs the programm. It's not so in vim but it happens in the Sublime Editor and when you invoke runhaskell. So the best is to write you program in the separate file and then load it in the ghci and invoke the function main (which runs the sound rendering with the function dac).

Roadmap: where are we going?


The new version 5.3 is out. Support for modern Haskell and Csound, sync with global BPM

Let's look at the new features.

  • The project was updated to compile with new GHC 8.4.x. Also it was tested on previous compilers down to 7.8. So the CE should compile across 7.8 to 8.4 GHC compilers.

  • The library was updated to support latest Csound stable release 6.10. There are many new DSP algorithms available with this update. Among them there are many great filters like emulation of Korg 35 analog filter, or emulation of Roland TB-303 resonant filter, zero-delay feedback filters. You can find them at the module Csound.Air.Filter.

  • Also documentation, examples and tutorial were updated for recent changes.

  • This release features new effects useful for guitars. Like emulation of Roland Space echo (function tapeEcho or magnus) and ambient guitar effect (ambiEnv, ambiGuitar). The Space echo simulates behaviour of magnetic tape delay. Ambient guitar detects strike attacks in the audio signal and smoothes them down, so that they sound like pads.

  • New addition is built in BPM synchronization. User can set global BPM with function setBpm. Then it's possible to use functions that synchronize Hzs (function syn) and seconds (function takt) to global BPM. It's useful to align delay times and LFO rates with global BPM. Also module csound-sampler was updated to respond to changes in global BPM.

  • There are some additions to improve usability of the library like adding new instances for rendering to Csound files. Like rendering functions with arbitrary number of inputs and outputs and rendering of functions augmented with UIs.

  • New useful functions: brown for brownian noise, resizeGui for scaling GUIs window size.

The 5.2 is out. Virtual pedalboards, arrays, new OSC, full support for mono synthesizers, patch skins, all GEN-routines are implemented

New features:

  • Complete support for monophonic synthesizers:

    • The argument of mono synth was updated.

      Previously it was a pair of amplitude and frequency signals. But this representation doesn't captures the notion of note retrigger. We can not create the mono-synt with sharp attacks.

      Now this is fixed. We can use adsr140 or adsrMonoSynt functions to create mono synths with fixed attacks

    • monoSco - for playing scores with mono-synths

    • monoSched - for playing event streams with mono synt

    • atSco and atSched now work for mono synth too

  • The patch can change the skin. The Patch type has changed. Know it supports the change in common parameters. Right now the ccommon parameters include only Low-pass filter type. But this can be extended in future releases.

The idea is that we can parametrize the patch with some common arguments so that use can tweak them without revriting the algorithm.

The low-pass filter is a vital tool that defines the character of the synthesizer. With recent addition of several modern filter emulators (like Korg (korg_lp), or acid filter diode) it's good to be able to quickly switch the filters. We can do it for patches with function

   setFilter :: ResonFilter -> Patch a -> Patch a
  • Family of standard effects was added (see module Csound.Air.Fx.FxBox and the guide). The effects are kindly provided by Iain McCurdy (recoded from his original implementation in Csound).

    The effects have catchy names and are defined on wide variety of types. Let's briefly discuss the naming conventions:

    • adele - analog delay
    • pongy - ping pong delay
    • tort - distortion
    • flan - flanger
    • fowler - Envelope follower
    • phasy - phaser
    • crusher - bit-crusher
    • chory - stereo chorus
    • tremy - tremolo
    • pany - panning
    • revsy - reverse playback

Also there are set of presets that imply the notion of add a bit of effect or add a lot of effect. They are suffixed with number from 1 to 5. Like flan1 or tort3. Also if the effect support the tone knob (center frequency of LP filter) ter are suffixes b for bright color and m for muted color. For example tort2m or adele2b.

The effects are just functions from signals to signals:
  dac $ hall 0.2 $ adele2 0.5 0.25 $ flan2 $ tort1m $ asigs
  • UI widgets for standard effects.

    Alongside with effects there are functions to create widgets (UI-controls). They have the same naming convention only the prefix ui is added. For example: uiTort, uiAdele or uiHall. Also there are predefined presets like uiFlan2 or uiPhasy3. With presets we put the box in the initial state corresponding to the given preset. But lately we can change it with UI-controls.

    With this feature paired with functions fxHor, fxVer and fxGrid we can easily design our virtual pedalboards.

    It can be used like this:

    > let pedals = fxGrid 2 [uiFlan1, uiTort1, uiAdele2m 0.5 0.3, uiHall 0.25]
    > dac $ fxApply pedals $ (sawSeq [1, 0.5, 0.25] 2) * sqr 220
  • Complete list of GEN routines. This release adds GEN:

    * 25 bpExps --  Construct functions from segments of exponential curves in breakpoint fashion.,
    * 27 bpLins --  Construct functions from segments of straight lines in breakpoint fashion.
    * wave waveletTab -- Generates a compactly supported wavelet function.
    * farey fareyTab -- Fills a table with the Farey Sequence Fn of the integer n.
    * sone soneTab -- Generate a table with values of the sone function.
    * exp expTab -- rescaleExpTab Generate a table with values on the exp function.
    * tanh tanhTab -- rescaleTanhTab Generate a table with values on the tanh function.
    * 52 readMultichannel -- Creates an interleaved multichannel table from the specified source tables, in the format expected by the ftconv opcode.
    * 41 randDist -- Generates a random list of numerical pairs.
    * 42 rangeDist Generates a random distribution of discrete ranges of values.
    * 40 tabDist -- Generates a random distribution using a distribution histogram.
    * 43 readPvocex -- Loads a PVOCEX file containing a PV analysis.
    * 28 readTrajectoryFile -- Reads a text file which contains a time-tagged trajectory.
    * 24 readNumTab --  Reads numeric values from another allocated function-table and rescales them.
    * 21 dist, uniDist, linDist, triDist, expDist, biexpDist, gaussDist, cauchyDist, pcauchyDist, betaDist, weibullDist, poissonDist -- Generates tables of different random distributions.
    * 18 tabseg -- Writes composite waveforms made up of pre-existing waveforms.
    * 31 mixOnTab -- Mixes any waveform specified in an existing table.
    * 32 mixTabs -- Mixes any waveform, resampled with either FFT or linear interpolation.
    * 30 tabHarmonics -- Generates harmonic partials by analyzing an existing table.

    See the Csound docs for details of what table they produce. Also the signatures for windows creating tabs was updated. It became more specific.

  • Global arguments defined with Macros. We can create a Csound .csd file in our program and after that we can run it on anything which has Csound installed. It's desirable to be able to tweak some parameters after rendering or to have some global config arguments. In Csound we can do it with macroses. We can use macros name in the code adn then we can change the value of the macros with command line flag --omacro:Name=Value.

    From now on it's possible to do it with Haskell too. There are functions:

    readMacrosDouble  :: String -> Double -> D
    readMacrosInt     :: String -> Int -> D
    readMacrosString  :: String -> String -> Str

    The first argument is a macro name and the second one is the default value which is used if no value is set in the flags.

  • The useful function to trigger an table based envelope. It comes in two flavors. One is driven with event stream and another with just a signal. It's on when signal is non zero.

    trigTab :: Tab -> Sig -> Sig -> Sig
    trigTab tab duration triggerSignal
    type Tick = Evt Unit
    trigTabEvt :: Tab -> Sig -> Tick -> Sig
    trigTabEvt tab duration triggerSignal
  • New functions for UI widgets.

    • We can change the relative size of the window. If the widget is too large or too small we can rescale it with functions:

      type ScaleFactor = (Double, Double)
      resizeGui :: ScaleFactor -> Gui -> Gui
      resizeSource :: ScaleFactor -> Source a -> Source a

      They change the default minimal sizes for all widgets that are contained within the given widget.

    • Grid layout. We are familiar with functions ver and hor. With them we can place the widgets vertically or horizontally. But now it's also possible to place the widgets on the grid:

       grid :: Int -> [Gui] -> Gui

    The first argument specifies the number of elements in each row.

    There are handy grid functions for combining source-widgets:

       gridLifts :: Int -> ([a] -> b) -> [Source a] -> Source b

    It applies a list based function to a list of value producer widgets and places all widgets on the grid. The first argument is the same as with grid.

    • UI default sizes are a bit smaller now.
  • It compiles on GHC-7.8 again

  • New function whileRef for imperative while loops.

    whileRef :: Tuple st => st -> (st -> SE BoolSig) -> (st -> SE st) -> SE ()
    whileRef initState condition body

    It's used in this way. It stores the initial state in the reference (local variable) and the it starts to implement the body while the predicate returns true. Notice that the body is also updates the state.

  • New functions for OSC that make it easy to read OSC messages that are interpreted like signals. For example we have an OSC-routine for volume control. When message happens we update the value. It would be good to be able to just read the signal:

    listenOscVal :: (Tuple a, OscVal a) => OscRef -> String -> a -> SE a
    listenOscVal oscRef address initValue

    There are two useful aliases for this function. They read signals and pairs of signals:

    listenOscSig  :: OscRef -> String -> Sig  -> SE Sig
    listenOscSig2 :: OscRef -> String -> Sig2 -> SE Sig2
  • Adds loopers that preserve attacks when rescaling by tempo. They are based on temposcal Csound algorithm. The previous loopers were based on the mincer algorithm. It uses FFT under the hood which can smooth out the sharp attacks. It's undesirable for percussive loops. The temposcal adds the feature of preserving attacks.

See the functions:

   -- | reads stereo files with scaling
   scaleWav ::  Fidelity -> TempoSig -> PitchSig -> String -> Sig2

   -- | reads mono files with scaling
   scaleWav1 :: Fidelity -> TempoSig -> PitchSig -> String -> Sig

Also there are presets for scaling the drums or harmonic instruments (they set the appropriate fidelity):

   scaleDrum, scaleHarm :: TempoSig -> PitchSig -> String -> Sig2

The fidelity is the degree of the size of FFT window. The formula for window size: 2 ** (fidelity + 11).

Also the corresponding functions are added for csound-sampler.

   wavScale :: Fidelity -> TempoSig -> PitchSig -> String -> Sam
   wavScale1 :: Fidelity -> TempoSig -> PitchSig -> String -> Sam

   drumScale, harmScale :: TempoSig -> PitchSig -> String -> Sam
  • The type signatures for echo and pingPong where simplified. Now they don't use side effects and look like pure functions:

    echo :: MaxDelayTime -> Feedback -> Sig -> Sig
    pingPong :: DelayTime -> Feedback -> Balance -> Sig2 -> Sig2
  • Type signatures for functions randSkip and freqOf where generalized. Now they use signals for probabilities instead of constant numbers. So we can change the probability of skip of the event during performance.

  • New monophonic instruments are added in csound-catalog: fmBass1, fmBass2, dafunkLead and one polyphonic celloSynt. Those instrument serve a good example for building monophonic synthesizers with sharp attacks.

Experimental features:

  • Arrays, with all opcodes and functional traversals. See the guide for details details.

  • Imperative style instruments.

    With imperative style instruments we can create and invoke the instruments in Csound way. we can create an instrument and get it's unique identifier. Than we can schedule a note by that identifier.

    We can create an instrument that produces a sound with function:

    newOutInstr :: (Arg a, Sigs b) => (a -> SE b) -> SE (InstrRef a, b)

    It takes in a body of the instrument and gives back an instrument reference and a signal where the output is going to be written. Then we can invoke the notes just like we do it in the Csound with function scheduleEvent:

    scheduleEvent :: Arg a => InstrRef a -> D -> D -> a -> SE ()
    scheduleEvent instrRed delayStartTime duration arguments

    It takes in instrument reference, start time from the time of invocation, duration (all in seconds) and miscellaneous arguments. Notice that the instrument reference is parametrized by the type of arguments. This way we can not feed the wrong messages to the instrument.

    Also we can create procedures that produce no output but do something useful:

    newInstr :: Arg a => (a -> SE ()) -> SE (InstrRef a)

The 5.1 is out! Let's warm up our hearts with new bright ideas in this Cold winter! New features:


  • New data type for Patches! This change is incompatible but it brings better support for playing patches live! The polyphonic and monophonic patches are united with single data-type so we can play them with the same functions. Also now we can create layered patches to play several patches at the same time and also we can split the keyboard on sections to play different patches on different sections. It's useful feature available in many modern synthesizers. But here we can include any number of layers! and we can mix mono and poly instruments together!

See the guide on patches to read the details.

  • Hard and soft sync. Lots of functions added for hard and soft sync. Check out the module Csound.Air.Wave.Sync.

  • Morpheus is here. New cool granular synthesizer is included. It's based on partikkel opcode. The aim is to simplify the work-flow with partikkel opcode. The API is experimental right now and might change. See the module Csound.Air.Granular.Morpheus for details.

  • Rewrite for filters. Filters get new names that suppose the audio-quality of the filter. Also many filters were redesigned to unify the parameters (order of arguments and ranges). Check out the module Csound.Air.Filter.

  • Many great filters were added thanks to the work of Steven Yi. Now we can use

    • zero-delay filters: zlp, zhp, zbp, zladder, zdf2, zdf4.
    • diode ladder filter (famous acid sound of TB-303): diode, linDiode
    • Korg 35 filters: korg_lp, linKorg_lp, korg_hp

New classical analog-like filters:

  • Chebyshev type I and II low pass filters: lpCheb1, lpCheb2 (also there are high-pass versions)

  • new butterworth filters: clp

Named filters with specific character suggested with a name: plastic, wobble, trumpy, harsh.

  • Transforming the audio with impulse responses now is super easy. Check out the new functions monoIR, stereoIR from the module Csound.Air.Fx. With those functions we can easily add complicated and beautiful reverbs from natural environments or classical reverberation units. There are plenty IR resources you can find out on the WEB. Also it adds the cool zconv function for zero convolution delay kindly provided by Victor Lazzarini.

  • Cabbage support. Adds full support for building cabbage interfaces. Checkout the module Csound.Cabbage. We can create vst-plugins with it! Still needs help for testing. We can check out the tutorial on how to build cabbage interfaces with csound-expression library: Cabbage guide.

  • Useful aliases for classic reverbs with single dry-wet ratio as a parameter: room, chamber, hall, cave. We can use it like this: dac $ hall 0.25 mySynt instead of dec $ mixAt 0.25 largeHall2 mySynt.

  • Raw waveforms for analogue-like oscillators: rawSaw, rawTri, rawSqr non-band limited based on table lookup. Can be useful for LFOs or more light-weight versions of oscillators than saw, tri or sqr.

  • mul' new scaling function. Scaling with side-effects. Can be useful to scale with random envelope.

  • Adds table read and write opcodes. Adds opcodes tablewa, tablew, readTab, readTable, readTable3, readTablei. See the module Csound.Tab for details.

  • Convenient aliases for reading from audio-files to tables. New names wavLeft, wavRight, mp3Left, mp3Right to read audio by channels. Also we can read both channels with functions wavs and mp3s.

  • Support for up to 8 outputs. More instances for RenderCsd were added. Now we can play back up to 8 signals at the same time!

  • Useful option to suppress the event printing on the screen. By default the Csound prints out every message on the screen (with time stamps and amplitudes). Now we have useful function noTrace to suppress those messages. Just write dacBy noTrace $ mySigs to stop them.

  • Adds More option setters for RT-audio engines. New option setters: setAlsa, setMme, setCoreAudio. Also it fixes the name of the RT-engine for OSX.


  • Adds randomized patterns with which we can skip the beats in the fixed pattern by given probability: rndPat and rndPat'.

The 5.0 is out! New features:


  • Microtonal tunings. We can use custom temperaments with insturments, patches, soundfonts and MIDI-instruments. Check out the guide on tuning and microtonal music (see also module Csound.Tuning). There are many predefined tunings (including ancient ones). Now we can play the authentic Bach music with Haskell! See Custom temperament. Microtonal music for details.

  • Functions for Csound API. We can interface with generated code through many other languages. We can generate the code with Haskell and the use it in other environments. we can build UI with Python or Clojure, we can create an Android synthesizer. See the guide section on Csound API. See Csound API. Using generated code with another languages for details.

  • Padsynth algorithm (need Csound 6.05). There are functions that makes it easy to use wonderful PADsynth algorithm, This algorithm is designed to make "alive" instruments, natural pads. There are not only function that explore the algorithm but also new PAtches in the package csound-catalog that are based on it! See the section in the guide on the PADsynth. Lot's of padsynth instruments are mode with morphing support. We can crossfade between 2 or even 4 timbres. See Padsynth algorithm for details.

  • Argument modifiers make it very convinient to modulate the rguments (apply vibrato to frequency or add some randomness to the parameter). See Arguments modulation for details.

  • The hard clipping was substituted with limiter. There should be no distortion when amplitude goes higher than 0dbfs value.

  • Adds Ping-pong delay implementation. See function pingPong at the module Csound.Air.Fx.

  • Adds Rory Walsh's brand new analog filters (need Csound 6.07). See functions alp1, alp2 and alp3 at the module Csound.Air.Filter.

  • Bugfixes for mixAt function. Now it doesn't duplicates the effectful-code. Now mixAt is not a function that is based on class At. It becomes a method in it's own class called MixAt. That fixes the code duplication problem.


  • new instruments that are based on PADsynth algorithm. Check out Csound.Patch at the section on PADsynth Sharc instruments. There are new deep spiritual vedic pads (vibhu, rishi, agni, prakriti, rajas, avatara, bhumi). See Padsynth algorithm for details.


  • adds some useful instances for class At and MixAt.

The 4.9.0 is out! New features:


  • Functions for creation of FM-synthesizers. We can create the whole graph of FM-units (with feedback). Check out the module Csound.Air.Fm

  • Support for Monosynth patches. See atMono in the module Csound.Air.Patch

  • Easy to use Binaural panning. See the module Csound.Air.Pan

  • Construction of patches for sound fonts (sfPatch, sfPatchHall).

  • Table of tables. We can create a table that contains tables.

  • Harmonic oscillators for subtractive synth: buz and gbuz

  • Reverbs for patches. It's very easy to add a reverb to your patch (withSmallHall patch, withLargeHall patch, etc)

  • Some bug-fixes


  • Many mono-synth were added. You can use them with function atMono in place of atMidi. The mono versions of patches have suffix m.

  • SHARC instruments. SHARC db contains a FFT-samples for sustain notes. It includes many orchestra instruments. There are many new patches that use natural sounding timbres taken from the SHARC library. Check out functions soloSharc, padSharc, dreamSharc.


  • Handy function withBpm allows to query current bpm with in the scope of expression.

  • Sampler mappers were generalized.

  • Char trigering functions are synchronized with bpm.

The 4.8.3 is out! New features:

This is a very important release to me. It tries to solve the problem present in the most open source music-production libraries. It's often the pack of beautiful sounds/timbres is missing. User is presented with many audio primitives but no timbres are present to show the real power of the framework. This release solves this problem. See the friend package csound-catalog on Hackage. It defines 200+ beautiful instruments ready to be used.

The csound-expression defines a new type called Patch for description of an instrument with a chain of effects. It's good place to start the journey to the world of music production.

There are new functions for synchronized reaction on events. The triggering of events can be synchronized with given BPM.

There examples are fixed and should work.

The library is updated for GHC-7.10!

The 4.8.2 is out! New features:

This release improves oscillators in many ways. Adds phase control to many standard oscillators. There are functions to detune oscillator and create unisions of oscillators (multioscillators or chorus effect).

Adds support for randomly generating events (with random frequency).

The 4.8 is out! New features:

A multitap looper is implemented (see Csound.Air.Looper). It's a powerful widget with lots of controls. We can create unlimited number of taps. And the length of the loops doesn't have to be the same for all taps. We can insert effects and even external controllers. And all this is packed as a simple function that produces a widget and the output signal. Three types of loopers are available one is for raw signal inputs, another for midi instruments and the last one is for soundfonts. You can see it in action at youtube.

There are lots of new step sequencers available. Pre 4.8 step sequencers could only produce signals with equal time segments but new step sequencers can play a tiny melodies. The API of temporal-media is supported for step sequencers (see Csound.Air.Envelope). There is a new type called Seq. It's for step sequencers that can play monophonic melodies.

There is a type class for humanization of envelopes. It works for linseg and step sequencers. It adds some amount of randomness to durations or values (see Csound.Air.Envelope HumanValue and HumanTime).

A midi chooser ui-box was implemented (see Csound.Air.Live, hmidiChooser, uiMidi). It makes it easy to choose a midi instrument among several alternatives. There are stand alone widgets and widgets implemented as an effect-box.

The class Compose from temporal-media package was broken to two classes: Harmony (with function hor) and Melody (with function mel).

The 4.7 is out! New features:

The Scores are redesigned! The low level CsdEventList is substituted with more advanced and flexible type Sco. The instruments are triggered not with pairs or triplets (individual events) but with scores!

The lib now depends on common APIs for delaying and composing values. There are common type classes for composition.

There is a simple API for composition of samples, notes and signal segments. The mel plays units sequentially, The hor plays units at the same time. The del delays the unit by given amount of time, The lim limits the unit in time. the loop creates infinite loops. The loopBy creates finite loops. The list of all functions can be found in the package temporal-media. See the module Temporal.Class.

I need to update the guide for changes!

The 4.6 is out! New features:

  • Granular delays and effects (see Csound.Air.Granular)

  • It's possible to create tables not only for reading but also for writing. We can create sound buffers (see newTab and newGlobalTab in the module Csound.Tab).

  • Hyper Vectorial Synthesis (HVS). Easy to use functions for HVS (see Csound.Air.Hvs) With HVS we can control lots of parameters with a couple of sliders. The HVS can reduce the size of control parameters by interpolating between snapshots of parameters.

  • New spectral functions for spectral fusion: crossSpecFilter and crossSpecVocoder (see Csound.Air.Spec)

  • New effect for playing input samples in segments (back and forth) trackerSplice (original design by Rory Walsh). With it we can extract segments of live audio and repeat them or play in reverse.

The 4.5 is out! New features:

  • Easy to use granular synthesis (see Csound.Air.Granular)

  • Support for opcode mincer. It's possible to scale pitch and tempo of audio files independently (see Csound.Air.Wav ram reading functions).

The 4.4 is out! New features:

  • Signal segments. With signal segments we can schedule audio signals with event streams. We can limit audio signals with clicks of the buttons or some other live events. We can retrigger samples, play them in sequence and perform many more actions shich are tied to the event streams.

  • Triggering samples with keyboard and midi-events (see Csound.Air.Sampler).