About JAsioHost

JAsioHost (JAH) is a Java interface to Steinberg's Audio Stream Input/Output (ASIO) API. It provides low-latecy (< 10ms) input and output access to the available audio hardware on Windows, replacing the need to use the outdated and slow Java Sound API.

Getting Started

JAsioHost comes in two parts, JAsioHost.jar and jasiohost.dll. The former is the usual encapsulation of the classes comprising the JAH Java library, and the latter is the JAH interface to ASIO. The package of JAH is com.synthbot.jasiohost.

The library can be quickly tested from the root directory of the project with java -jar JAsioHost.jar -Djava.library.path=./. The ExampleHost will launch a small GUI allowing you to select an available ASIO driver and use it to play a 440Hz tone. If you're not sure if you have the correct ASIO driver installed (usually soundcard-specific), then try using the excellent ASIO4ALL Universal ASIO Driver For WDM Audio.

• Include JAsioHost.jar in your Java project.
• Make jasiohost.dll available to your project. This can be done in several ways:
  • Move or copy the library to C:\WINDOWS\system32. This is the default search location for JNI libraries.
  • Inform the JVM where the library is located. This can be done with, e.g. java -Djava.library.path=C:\WINDOWS\system32

If the JVM cannot find the dll, an UnsatisfiedLinkError exception will be thrown.

Example

The basic design pattern for using JAsioHost is as follows. static methods in AsioDriver are used to collect information about the available drivers. getDriver is called in order to load and instantiate a given driver. The AsioDriver can then be queried for channel state information. Audio buffers are created using createBuffers, before start is called. Callbacks are made from the driver to registered AsioDriverListener objects in order to submit input and retrieve output.

// get a list of available ASIO drivers
List<String> driverNameList = AsioDriver.getDriverNames();

// load the names ASIO driver
AsioDriver asioDriver = AsioDriver.getDriver(driverNameList.get(0));

// add an AsioDriverListener in order to receive callbacks from the driver
asioDriver.addAsioDriverListener(new AsioDriverListener() {
  @Override
  public void bufferSwitch(long systemTime, long samplePosition, Set<AsioChannel> channels) {
    // fill in audio buffers here
  }
  
  // implement remaining AudioDriverListener interface functions
}

// create a Set of AsioChannels, defining which input and output channels will be used
Set<AsioChannel> activeChannels = new HashSet<AsioChannel>();

// configure the ASIO driver to use the given channels
activeChannels.add(asioDriver.getChannelOutput(0));
activeChannels.add(asioDriver.getChannelOutput(1));

// create the audio buffers and prepare the driver to run
asioDriver.createBuffers();

// start the driver
asioDriver.start();
try {
  Thread.sleep(1000);
} catch (InterruptedException ie) {
  ie.printStackTrace(System.err);
}

// tear everything down
AsioDriver.shutdownAndUnloadDriver();

See the ExampleHost for more details. It also contains a main function with a minimum GUI for selecting available drivers.

Note that you can only load one ASIO driver at time. This is a limitation of the original API (AFAIK).

Note on Compilation

If you are brave enough to try to compile the native component, please note the following helpful tips:

• I use Cygwin to compile the library, and not Visual Studio. Because I am more familiar with the Unix toolchain. This makes some things more difficult. Unfortunate, but so be it.
• You must download your own copy of the ASIO library. It cannot be distributed here due to licensing restrictions by Steinberg.

In the ASIO library,

• ./common/asiodrvr.cpp is not necessary. Rename or remove it.
• ./common/dllentry.cpp is not necessary. Rename or remove it.
• Line 219 of ./common/combase.h, #if WINVER < 0x0501, should be replaced with #if 0. See here for more information.

A Note about API Translation

The JAsioHost API does not strictly reflect the original C++ API written by Steinberg. There are two reasons for this. The first is that some elements of the original API do not translate well due to language semantics. The second is that I felt that some things could be improved or simplified.

An example of the former is that the native API refers to an audio buffer by using a void pointer. Java does not allow arrays to be referenced opaquely. JAsioHost therefore encapsulates an audio buffer by using a ByteBuffer, which exposes the raw bytes of the native buffer, but also allows other types to be read and written with relative ease.

An example of the latter is the absence of the ASIOBufferInfo structure in Java. I simply added a reference to the audio buffer to the active AsioChannel objects. As the audio buffer conceptually belongs to a channel, this seemed to make sense, and also remove a superfluous class.

License

JAsioHost is released under the Lesser Gnu Public License (LGPL). Basically, the library stays open source, but you can use if for whatever you want, including closed source applications. You must publicly credit the use of this library.

Acknowledgements

Many thanks to the following people for making JAsioHost possible:

• Steinberg for releasing ASIO and making good documentation! Of course the ASIO API belongs to them, and if you want to be able to compile the native source then you will need to get the ASIO component from them.
• This project depends on IASIOThisCallResolver. Without it, this project would not be possible. All hail IASIOThisCallResolver. P.S. The reason for this is that I use Cygwin, gcc, MinGW in order to build the native component, not Visual Studio.
• Steve Taylor of http://toot.org.uk for his help in testing out various ASIO drivers and assisting in the debugging process.
• Carl Janson of HD Sound Lab for his efforts in compiling a 64-bit version of the native library.