LV2

A filter that changes the phase relationship between frequency components.

A plugin that primarily changes the volume of its input.

A plugin that analyses its input and emits some useful information.

A port connected to an array of float audio samples.

Ports of this type are connected to a buffer of float audio samples, which the host guarantees have sample_count elements in any call to LV2_Descriptor::run().

Audio samples are normalized between -1.0 and 1.0, though there is no requirement for samples to be strictly within this range.

A filter that attenuates frequencies outside of some band.

A port connected to an array of float control values.

Ports of this type have the same buffer format as an AudioPort, except the buffer represents audio-rate control data rather than audio. Like a ControlPort, a CV port SHOULD have properties describing its value, in particular minimum, maximum, and default.

Hosts may present CV ports to users as controls in the same way as control ports. Conceptually, aside from the buffer format, a CV port is the same as a control port, so hosts can use all the same properties and expectations.

In particular, this port type does not imply any range, unit, or meaning for its values. However, if there is no inherent unit to the values, for example if the port is used to modulate some other value, then plugins SHOULD use a normalized range, either from -1.0 to 1.0, or from 0.0 to 1.0.

It is generally safe to connect an audio output to a CV input, but not vice-versa. Hosts must take care to prevent data from a CVPort port from being used as audio.

An individual channel, such as left or right.

A specific channel, for example the left channel of a stereo stream. A channel may be audio, or another type such as a MIDI control stream.

An effect that mixes significantly delayed copies of its input.

A filter that adds a delayed version of its input to itself.

A plugin that reduces the dynamic range of its input.

A plugin that emits constant values.

A port connected to a single `float`.

A plugin that converts its input into a different form.

An effect that intentionally delays its input as an effect.

A designation which defines the meaning of some data.

A designation is metadata that describes the meaning or role of something. By assigning a designation to a port using designation, the port's content becomes meaningful and can be used more intelligently by the host.

A plugin that adds distortion to its input.

A plugin that alters the envelope or dynamic range of its input.

A plugin that adjusts the balance between frequency components.

A plugin that applies an envelope to its input.

A plugin that expands the dynamic range of its input.

Additional data defined by an extension.

This is additional data that a plugin may return from LV2_Descriptor::extension_data(). This is generally used to add APIs to extend that defined by LV2_Descriptor.

An additional feature which may be used or required.

An effect that manipulates the frequency spectrum of its input.

An effect that mixes slightly delayed copies of its input.

A plugin whose output is a mathematical function of its input.

A plugin that attenuates signals below some threshold.

A plugin that generates new sound internally.

A filter that attenuates frequencies below some cutoff.

A port connected to constant data which is read during `run()`.

A plugin intended to be played as a musical instrument.

A plugin that limits its input to some maximum level.

A filter that attenuates frequencies above some cutoff.

A plugin that primarily processes MIDI messages.

A string in Markdown syntax.

This datatype is typically used for documentation in Markdown syntax.

Generally, documentation with this datatype should stay as close to readable plain text as possible, but may use core Markdown syntax for nicer presentation. Documentation can assume that basic extensions like codehilite and tables are available.

A plugin that mixes some number of inputs into some number of outputs.

An effect that modulats its input as an effect.

A plugin that adjusts the balance between a fixed set of frequency components.

A plugin that generates output with an oscillator.

A port connected to data which is written during `run()`.

A plugin that adjusts the balance between configurable frequency components.

A property that is a plugin parameter.

A parameter is a designation for a control.

A parameter defines the meaning of a control, not the method of conveying its value. For example, a parameter could be controlled via a ControlPort, messages, or both.

A ControlPort can be associated with a parameter using designation.

An effect that periodically sweeps a filter over its input.

A plugin that shifts the pitch of its input.

An LV2 plugin.

To be discovered by hosts, plugins MUST explicitly have an rdf:type of Plugin in their bundle's manifest, for example:

<http://example.org/my-plugin> a lv2:Plugin .

Plugins should have a doap:name property that is at most a few words in length using title capitalization, for example Tape Delay Unit.

Base class for a plugin-like resource.

An abstract plugin-like resource that may not actually be an LV2 plugin, for example that may not have a binary. This is useful for describing things that share common structure with a plugin, but are not themselves an actual plugin, such as presets.

An interesting point in a value range.

• A Point MUST have at least one rdfs:label which is a string.

• A Point MUST have exactly one rdf:value with a type that is compatible with the type of the corresponding Port.

An LV2 plugin port.

All LV2 port descriptions MUST have a rdf:type that is one of Port, InputPort or OutputPort. Additionally, there MUST be at least one other rdf:type which more precisely describes type of the port, for example AudioPort.

Hosts that do not support a specific port class MUST NOT instantiate the plugin, unless that port has the connectionOptional property set.

A port has two identifiers: a (numeric) index, and a (textual) symbol. The index can be used as an identifier at run-time, but persistent references to ports (for example in presets or save files) MUST use the symbol. Only the symbol is guaranteed to refer to the same port on all plugins with a given URI, that is the index for a port may differ between plugin binaries.

Base class for a port-like resource.

Similar to PluginBase, this is an abstract port-like resource that may not be a fully specified LV2 port. For example, this is used for preset "ports" which do not specify an index.

A particular property that a port has.

An effect that adds reverberation to its input.

A single `float` Point for control inputs.

A plugin that aims to emulate some environmental effect or musical equipment.

A plugin that manipulates the position of audio in space.

An LV2 specifiation.

An LV2 specification typically contains a vocabulary description, C headers to define an API, and any other resources that may be useful. Specifications, like plugins, are distributed and installed as bundles so that hosts may discover them.

A plugin that alters the spectral properties of audio.

A short restricted name used as a strong identifier.

The first character of a symbol must be one of _, a-z or A-Z, and subsequent characters may additionally be 0-9. This is, among other things, a valid C identifier, and generally compatible in most contexts which have restrictions on string identifiers, such as file paths.

A utility plugin that is not a typical audio effect or generator.

An effect that alters the shape of input waveforms.

The plugin this resource is related to.

This is primarily intended for discovery purposes: bundles that describe resources that work with particular plugins (like presets or user interfaces) SHOULD specify this in their manifest.ttl so the host can associate them with the correct plugin. For example:

<thing>
    a             ext:Thing ;
    lv2:appliesTo <plugin> ;
    rdfs:seeAlso  <thing.ttl> .

Using this pattern is preferable for large amounts of data, since the host may choose whether/when to load the data.

The binary of this resource.

The value of this property must be the URI of a shared library object, typically in the same bundle as the data file which contains this property. The actual type of the library is platform specific.

This is a required property of a Plugin which MUST be included in the bundle's manifest.ttl file. The binary of a Plugin is the shared object containing the lv2_descriptor() or lv2_lib_descriptor() function. This probably may also be used similarly by extensions to relate other resources to their implementations (it is not implied that a binary on an arbitrary resource is an LV2 plugin library).

The default value for this control.

The host SHOULD set the port to this value initially, and in any situation where the port value should be cleared or reset.

The designation that defines the meaning of this input or output.

This property is used to give a port's contents a well-defined meaning. For example, if a port has the designation eg:gain, then the value of that port represents the eg:gain of the plugin instance.

Ports should be given designations whenever possible, particularly if a suitable designation is already defined. This allows the host to act more intelligently and provide a more effective user interface. For example, if the plugin has a BPM parameter, the host may automatically set that parameter to the current tempo.

Extended documentation.

Relates a Resource to extended documentation.

LV2 specifications are documented using this property with an Markdown datatype.

If the value has no explicit datatype, it is assumed to be a valid XHTML Basic 1.1 fragment suitable for use as the content of the body element of a page.

XHTML Basic is a W3C Recommendation which defines a simplified subset of XHTML intended to be reasonable to implement with limited resources, for exampe on embedded devices. See XHTML Basic, Section 3 for a list of valid tags.

Whether processing is currently enabled (not bypassed).

If this value is greater than zero, the plugin processes normally. If this value is zero, the plugin is expected to bypass all signals unmodified. The plugin must provide a click-free transition between the enabled and disabled (bypassed) states.

Values less than zero are reserved for future use (such as click-free insertion/removal of latent plugins), and should be treated like zero (bypassed) by current implementations.

Extension data provided by a plugin or other binary.

If a plugin has a value for this property, it must be a URI that defines the extension data. The plugin should return the appropriate data when LV2_Descriptor::extension_data() is called with that URI as a parameter.

Whether processing is currently free-wheeling.

If true, this means that all processing is happening as quickly as possible, not in real-time. When free-wheeling there is no relationship between the passage of real wall-clock time and the passage of time in the data being processed.

A non-negative zero-based 32-bit index.

The latency introduced, in frames.

The maximum value for this control.

This is a soft limit: the plugin is required to gracefully accept all values in the range of a port's data type.

The micro version of this resource.

Releases of plugins and extensions MUST be explicitly versioned. Correct version numbers MUST always be maintained for any versioned resource that is published. For example, after a release, if a change is made in the development version in source control, the micro version MUST be incremented (to an odd number) to distinguish this modified version from the previous release.

This property describes half of a resource version. For detailed documentation on LV2 resource versioning, see minorVersion.

The minimum value for this control.

This is a soft limit: the plugin is required to gracefully accept all values in the range of a port's data type.

The minor version of this resource.

This, along with microVersion, is used to distinguish between different versions of the same resource, for example to load only the bundle with the most recent version of a plugin. An LV2 version has a minor and micro number with the usual semantics:

• The minor version MUST be incremented when backwards (but not forwards) compatible additions are made, for example the addition of a port to a plugin.

• The micro version is incremented for changes which do not affect compatibility at all, for example bug fixes or documentation updates.

Note that there is deliberately no major version: all versions with the same URI are compatible by definition. Replacing a resource with a newer version of that resource MUST NOT break anything. If a change violates this rule, then the URI of the resource (which serves as the major version) MUST be changed.

Plugins and extensions MUST adhere to at least the following rules:

• All versions of a plugin with a given URI MUST have the same set of mandatory (not connectionOptional) ports with respect to symbol and rdf:type. In other words, every port on a particular version is guaranteed to exist on a future version with same symbol and at least those rdf:types.

• New ports MAY be added without changing the plugin URI if and only if they are connectionOptional and the minor version is incremented.

• The minor version MUST be incremented if the index of any port (identified by its symbol) is changed.

• All versions of a specification MUST be compatible in the sense that an implementation of the new version can interoperate with an implementation of any previous version.

Anything that depends on a specific version of a plugin (including referencing ports by index) MUST refer to the plugin by both URI and version. However, implementations should be tolerant where possible.

When hosts discover several installed versions of a resource, they SHOULD warn the user and load only the most recent version.

An odd minor or micro version, or minor version zero, indicates that the resource is a development version. Hosts and tools SHOULD clearly indicate this wherever appropriate. Minor version zero is a special case for pre-release development of plugins, or experimental plugins that are not intended for stable use at all. Hosts SHOULD NOT expect such a plugin to remain compatible with any future version. Where feasible, hosts SHOULD NOT expose such plugins to users by default, but may provide an option to display them.

A display name for labeling in a user interface.

Unlike symbol, this is unrestricted, may be translated, and is not relevant for compatibility. The name is not necessarily unique and MUST NOT be used as an identifier.

An optional feature that is supported if available.

To support this feature, the host MUST pass its URI and any additional data to the plugin in LV2_Descriptor::instantiate().

The plugin MUST NOT fail to instantiate if an optional feature is not supported by the host.

A port (input or output) on this plugin.

A property of this port hosts may find useful.

States that a port has a particular PortProperty. This may be ignored without catastrophic effects, though it may be useful, for example to provide a sensible user interface for the port.

The project this is a part of.

This property provides a way to group plugins and/or related resources. A project may have useful metadata common to all plugins (such as homepage, author, version history) which would be wasteful to list separately for each plugin.

Grouping via projects also allows users to find plugins in hosts by project, which is often how they are remembered. For this reason, a project that contains plugins SHOULD always have a doap:name. It is also a good idea for each plugin and the project itself to have an symbol property, which allows nice quasi-global identifiers for plugins, for example myproj.superamp which can be useful for display or fast user entry.

The prototype to inherit properties from.

This property can be used to include common properties in several descriptions, serving as a sort of template mechanism. If a plugin has a prototype, then the host must load all the properties for the prototype as if they were properties of the plugin. That is, if :plug prototype :prot, then for each triple :prot p o, the triple :plug p o should be loaded.

This facility is useful for distributing data-only plugins that rely on a common binary, for example those where the internal state is loaded from some other file. Such plugins can refer to a prototype in a template LV2 bundle which is installed by the corresponding software.

A required feature that must be available to run.

To support this feature, the host MUST pass its URI and any additional data to the plugin in LV2_Descriptor::instantiate().

The host MUST check this property before attempting to instantiate a plugin, and not attempt to instantiate plugins which require features it does not support. The plugin MUST fail to instantiate if a required feature is not supported by the host. Note that these rules are intentionally redundant for resilience: neither host nor plugin should assume that the other does not violate them.

A scale point of a port or parameter.

A short display name for labeling in a user interface.

This is the same as name, with the additional requirement that the value is shorter than 16 characters.

The symbol that identifies this resource in the context of its parent.

The value of this property MUST be a valid Symbol, and MUST NOT have a language tag.

A symbol is a unique identifier with respect to the parent, for example a port's symbol is a unique identifiers with respect to its plugin. The plugin author MUST change the plugin URI if any port symbol is changed or removed.

The property that this port may be connected to NULL.

This property means that the port does not have to be connected to valid data by the host. To leave a port unconnected, the host MUST explicitly connect the port to NULL.

The primary control channel.

This should be used as the designation of ports that are used to send commands and receive responses. Typically this will be an event port that supports some protocol, for example MIDI or LV2 Atoms.

Control port scale points represent all useful values.

Indicates that all the rasonable values for a port are defined by scalePoint properties. For such ports, a user interface should provide a selector that allows the user to choose any of the scale point values by name. It is recommended to show the value as well if possible.

Note that this is only a hint, and that the plugin MUST operate reasonably even if such a port has a value that does not correspond to a scale point.

Plugin is capable of running in a hard real-time environment.

This feature indicates that the plugin is capable of running in a hard real-time environment. This should be the case for most audio processors, so most plugins are expected to have this feature.

To support this feature, plugins MUST adhere to the following in all of their audio class functions (LV2_Descriptor::run() and LV2_Descriptor::connect_port()):

• There is no use of malloc(), free() or any other heap memory management functions.

• There is no use of any library functions which do not adhere to these rules. The plugin may assume that the standard C math library functions are safe.

• There is no access to files, devices, pipes, sockets, system calls, or any other mechanism that might result in the process or thread blocking.

• The maximum amount of time for a run() call is bounded by some expression of the form A + B * sample_count, where A and B are platform specific constants. Note that this bound does not depend on input signals or plugin state.

Plugin requires separate locations for input and output.

This feature indicates that the plugin may not work correctly if the host elects to use the same data location for both input and output. Plugins that will fail to work correctly if ANY input port is connected to the same location as ANY output port MUST require this feature. Doing so should be avoided whenever possible since it prevents hosts from running the plugin on data in-place.

Control port values are treated as integers.

Indicates that all the reasonable values for a port are integers. For such ports, a user interface should provide a stepped control that only allows choosing integer values.

Note that this is only a hint, and that the plugin MUST operate reasonably even if such a port has a non-integer value.

Plugin has a real-time dependency.

This feature is for plugins that have time-sensitive internals, for example communicating in real time over a socket. It indicates to the host that its input and output must not be cached or subject to significant latency, and that calls to LV2_Descriptor::run() should be made at a rate that roughly corresponds to wall clock time (according to the sample_count parameter).

Note that this feature is not related to hard real-time execution requirements (see hardRTCapable).

Signal for port should not be considered a main input or output.

Indicates that a port is a sidechain, which affects the output somehow but should not be considered a part of the main signal chain. Sidechain ports SHOULD be connectionOptional, and may be ignored by hosts.

Control port value is the plugin latency in frames.

This property indicates that the port is used to express the processing latency incurred by the plugin, expressed in samples. The latency may be affected by the current sample rate, plugin settings, or other factors, and may be changed by the plugin at any time. Where the latency is frequency dependent the plugin may choose any appropriate value. If a plugin introduces latency it MUST provide EXACTLY ONE port with this property set. In fuzzy cases the value should be the most reasonable one based on user expectation of input/output alignment. For example, musical delay plugins should not report their delay as latency, since it is an intentional effect that the host should not compensate for.

This property is deprecated, use a designation of latency instead, following the same rules as above:

<http://example.org/plugin>
    lv2:port [
        a lv2:OutputPort , lv2:ControlPort ;
        lv2:designation lv2:latency ;
        lv2:symbol "latency" ;
    ]

Control port bounds are interpreted as multiples of the sample rate.

Indicates that any specified bounds should be interpreted as multiples of the sample rate. For example, a frequency range from 0 Hz to the Nyquist frequency (half the sample rate) can be specified by using this property with minimum 0.0 and maximum 0.5. Hosts that support bounds at all MUST support this property.

Control port value is considered a boolean toggle.

Indicates that the data item should be considered a boolean toggle. Data less than or equal to zero should be considered off or false, and data above zero should be considered on or true.