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IDirectMusicSynth and IDirectMusicSynthSink

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As described in Synthesizers and Wave Sinks, you can implement a custom software synthesizer or wave sink that runs in user mode and communicates with DirectMusic. The synthesizer object must have an IDirectMusicSynth interface. The wave sink object must have an IDirectMusicSynthSink interface.

DirectMusic communicates with a software synthesizer through its IDirectMusicSynth interface. DirectMusic supports this interface in DirectX 6.1 and later. IDirectMusicSynth supports the methods shown in the following table, which organizes the methods into functional groups.

Group Method Names
Activation IDirectMusicSynth::Activate
Channels IDirectMusicSynth::GetChannelPriority, IDirectMusicSynth::SetChannelPriority
Instruments IDirectMusicSynth::Download, IDirectMusicSynth::Unload
Information IDirectMusicSynth::GetAppend, IDirectMusicSynth::GetFormat, IDirectMusicSynth::GetLatencyClock, IDirectMusicSynth::GetPortCaps , IDirectMusicSynth::GetRunningStats
Playback IDirectMusicSynth::PlayBuffer, IDirectMusicSynth::Render
Ports IDirectMusicSynth::Open, IDirectMusicSynth::Close, IDirectMusicSynth::SetNumChannelGroups
Miscellaneous parameters IDirectMusicSynth::SetMasterClock, IDirectMusicSynth::SetSynthSink

Most applications do not need to call the methods in the IDirectMusicSynth interface directly; the DirectMusic port typically manages the synthesizer. However, your application can interface directly to the synthesizer during development and testing.

The synthesizer is not complete without a connection to a wave sink, which is represented as an object with an IDirectMusicSynthSink interface. The wave sink connects the synthesizer's audio output stream to an audio rendering module such as DirectSound, DirectShow, or the Windows Multimedia waveOut API.

By default, DirectMusic uses its internal IDirectMusicSynthSink implementation to handle the wave data that the software synthesizer generates. This wave sink feeds the data to DirectSound.

Before the synthesizer can be activated, a wave sink must first be created and connected to the synthesizer via a call to IDirectMusicSynth::SetSynthSink. This should be the very first call after creating the synthesizer because many of the timing-related calls, including IDirectMusicSynth::GetLatencyClock and IDirectMusicSynth::SetMasterClock, are actually passed through to equivalent calls on IDirectMusicSynthSink.

Only DirectX 6.1 and DirectX 7 support the implementation of a custom user-mode wave sink with an IDirectMusicSynthSink interface. IDirectMusicSynthSink supports the methods shown in the following table, which organizes the methods into functional groups.

Group Method Names
Initialization IDirectMusicSynthSink::Activate, IDirectMusicSynthSink::GetDesiredBufferSize
IDirectMusicSynthSink::Init, IDirectMusicSynthSink::SetDirectSound
Timing IDirectMusicSynthSink::GetLatencyClock, IDirectMusicSynthSink::RefTimeToSample
IDirectMusicSynthSink::SampleToRefTime, IDirectMusicSynthSink::SetMasterClock

In DirectX 8 and later, DirectMusic always uses its internal wave sink with a user-mode synthesizer. These later versions of DirectMusic do not support custom implementations of IDirectMusicSynthSink.

In DirectX 6.1 and DirectX 7, however, you are free to implement your own IDirectMusicSynthSink object and use it to manage the synthesizer's audio output stream in any way you like. For example, you might feed the wave data into DirectShow or the waveOut API. If you create a wave stream object, it must have an IDirectMusicSynthSink interface to plug into the IDirectMusicSynth object.

In addition to managing the wave stream, the wave sink is responsible for controlling the timing for the synthesizer. The wave sink receives the master clock by a call to IDirectMusicSynth::SetMasterClock, which passes the master time source on with an identical call to IDirectMusicSynthSink::SetMasterClock. Because the master clock is not generated from the same crystal as the wave stream, the wave sink must keep them synchronized by compensating for clock drift.

Additionally, so that the synthesizer can keep track of time appropriately, it provides two calls to convert from master clock time to sample time and back:

  • IDirectMusicSynthSink::RefTimeToSample

  • IDirectMusicSynthSink::SampleToRefTime

The wave sink generates the latency clock because it actually manages the times at which samples get written by calls to IDirectMusicSynth::Render. When DirectMusic calls IDirectMusicSynth::GetLatencyClock on the DirectMusic port, it simply turns around and calls IDirectMusicSynthSink::GetLatencyClock.

When a software synthesizer is first opened, DirectMusic gives the synthesizer a DMUS_PORTPARAMS structure (described in the Microsoft Windows SDK documentation) that specifies the sample rate and number of channels for the audio output stream. The synthesizer then converts these into a standard WAVEFORMATEX structure that it passes to the wave sink when the wave sink calls the IDirectMusicSynth::GetFormat method.

For additional information, see the descriptions of the IDirectMusic and IDirectMusicPort interfaces in the Windows SDK documentation.