This sample shows how to use the APIs in the Windows.Media.Audio namespace to create audio graphs for audio routing, mixing, and processing scenarios. An audio graph is a set of interconnected audio nodes through which audio data flows. Audio input nodes supply audio data to the graph from audio input devices, audio files, or from custom code. Audio output nodes are the destination for audio processed by the graph. Audio can be routed out of the graph to audio output devices, audio files, or custom code. The last type of node is a submix node which takes audio from one or more nodes and combines them into a single output that can be routed to other nodes in the graph. After all of the nodes have been created and the connections between them set up, you simply start the audio graph and the audio data flows from the input nodes, through any submix nodes, to the output nodes. This model makes scenarios like recording from a device's microphone to an audio file, playing audio from a file to a device's speaker, or mixing audio from multiple sources quick and easy to implement.
Additional scenarios are enabled with the addition of audio effects to the audio graph. Every node in an audio graph can be populated with zero or more audio effects that perform audio processing on the audio passing through the node. There are several built-in effects such as echo, equalizer, limiting, and reverb that can be attached to an audio node with just a few lines of code. You can also create your own custom audio effects that work exactly the same as the built-in effects.
This sample demonstrates several common scenarios for routing and processing audio with an audio graph:
Scenario 1: File Playback:
Press the Load File button and file picker is shown that lets you pick an audio file to play. After selecting a file, press Start Graph to start playback of the file. The Loop toggle switch lets you toggle looping of the file on and off. The Playback Speed slider lets you adjust the playback speed.
In the code-behind for this scenario, an AudioGraph is created and two nodes are added: an AudioDeviceOutputNode, which represents the default audio output device, and an AudioFileInputNode, which represents the audio file that you select. A connection is added from the input node to the output node. When the audio graph is started, the audio data flows from the file input node to the device output node.
Scenario 2: Device Capture:
In this scenario, audio is recorded from an input device to an audio file while being monitored on an output device. First, select the audio device that will be used for monitoring from the list box. Press the Pick Output File to launch a file save picker that lets you choose the file to which audio will be recorded. Press Create Graph to create the audio graph with the selected inputs and outputs. Press the Record button to begin recording from the device input to the audio file. Press the Stop button to stop recording.
In the code-behind for this scenario, an AudioGraph is created with three nodes: an AudioDeviceInputNode, an AudioDeviceOutputNode, and a AudioFileOutputNode. A connection is added from the AudioDeviceInputNode to the AudioDeviceOutputNode, and another connection is added from the AudioDeviceInputNode to the AudioFileOutputNode. When the Record button is clicked, audio flows from the input node to the two output nodes. Also of note in this scenario is that the quantum size, or the amount of audio data that is processed at one time, is set to LowestLatency, which means that the audio processing will have the lowest latency possible on the device. This also means that device disconnection errors must be handled.
Scenario 3: Frame Input Node:
This scenario shows how to generate and route audio data into an audio graph from custom code. Press the Generate Audio button to start generating audio from custom code.
Press Stop to stop the audio.
In the code-behind for this scenario an AudioGraph is created with two nodes: an AudioFrameInputNode that represents the custom audio generation code and which is connected to an AudioDeviceOutputNode representing the default output device. The AudioFrameInputNode is created with the same encoding as the audio graph so that the generated audio data has the same format as the graph. Once the audio graph is started, the QuantumStarted event is raised by the audio graph whenever the custom code needs to provide more audio data. The custom code creates a new AudioFrame object in which the audio data is stored. The example accesses the underlying buffer of the AudioFrame, which requires an unsafe code block, and inserts values from a sine wav into the buffer. The AudioFrame containing the audio data is then added to the AudioFrameInputNode list of frames ready to be processed, which is then consumed by the audio graph and passed to the audio device output node.
Scenario 4: Submix Nodes:
In this scenario, audio from two audio files is mixed together and an audio echo effect is added to the mix before the audio is routed to the output device. Press Load File 1 to select the first audio file and Load File 2 to select the second file. Press Start Graph to start the flow of audio through the graph. Use the Echo button to toggle the echo effect on and off while the graph is running.
The AudioGraph for this scenario has four nodes: two AudioFileInputNode objects, an AudioDeviceOutputNode, and an AudioSubmixNode. The file input nodes are connected to the submix node which is connected to the audio device output node. An EchoEffectDefinition object representing the built-in echo effect is created and added to the EffectDefinitions list of the submix node. The EnableEffectsByDefinition and DisableEffectsByDefinition methods are used to toggle the effect on and off. The effect model shown in this example is implemented by all audio node types, so you can add effects at any point in the audio graph. Also, submix nodes can be chained together to easily create mixes with complex layering of effects.
Scenario 5: In-box Effects:
This example demonstrates each of the effects that are built-in to the platform. These include:
- Echo
- Reverb
- Equalizer
- Limiter
The UI for this scenario lets you load an audio file to play back and then toggle these effects on and off and adjust their parameters.
The code-behind for this scenario uses just two nodes. An AudioFileInputNode and a AudioDeviceOutputNode. The effects are initialized and then added to the EffectDefinitions list of the file input node.
Scenario 6: Custom Effects:
This scenario demonstrates how to create an custom audio effect and then using it in an audio graph. Press the Load File button to select an audio file to play. Press Start Graph to begin playback of the file with the custom effect.
The custom effect for this scenario is defined in a single file, CustomEffect.cs, that is included in its own project. The class implemented in this file, AudioEchoEffect, implements the IBasicAudioEffect interface which allows it to be used in an audio graph. The actual audio processing is implemented in the ProcessFrame method. The audio graph calls this method and passes in a ProcessAudioFrameContext object which provides access to AudioFrame objects representing the input to the effect and the output from the effect. The effect implements a simple echo by storing samples from the input frame in a buffer and then adding the samples previously stored in the buffer to the current input samples and then inserting thos values into the output frame buffer.
The custom effect has a property set that can be modified by calling the SetProperties method. The custom effect exposes a Mix property through the property set that is used to control the amount of echo that is added back into the original signal.
[Windows.Media.Audio namespace] (https://msdn.microsoft.com/en-us/library/windows/apps/windows.media.audio.aspx)
Client: Windows 10
Phone: Windows 10
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