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Posted 21 Mar 2008

Low Latency Audio using ASIO Drivers in .NET

, 7 May 2008
Demonstrates access to your sound hardware with ASIO drivers
// BlueWave.Interop.Asio by Rob Philpott. Please send all bugs/enhancements to
//  This file and the code contained within is freeware and may be
// distributed and edited without restriction. You may be bound by licencing restrictions
// imposed by Steinberg - check with them prior to distributing anything.

#pragma once
#pragma managed
using namespace System;

#include "AsioRedirect.h"

namespace BlueWave
	namespace Interop
		namespace Asio
				// represents an ASIO driver (also some static for all drivers)
				public ref class AsioDriver

					// we'll maintain a list of drivers
					static array<InstalledDriver^>^ _installedDrivers;

					// but you can only have one active at once
					static AsioDriver^ _instance;

					// our elusive COM interface
					IAsio* _pDriver;

					// a struct which specifies callback addresses
					ASIOCallbacks* _pCallbacks;

					// the number of input channels supported by the driver, and our max
					int _nInputs;

					// and the number of output channels
					int _nOutputs;

					// is it usefull to call outputReady each time we have updated the outputbuffers 
					ASIOError _outputReadySupport;

					// the static callback methods - we'll forward these to instance members
					static void OnSampleRateDidChange(ASIOSampleRate rate);
					static long OnAsioMessage(long selector, long value, void* message, double* opt);

					// select a driver once an instance of this class has been created
					void InternalSelectDriver(InstalledDriver^ installedDriver);

					// our instance based handlers
					void OnBufferSwitch(long doubleBufferIndex, ASIOBool directProcess);
					ASIOTime* OnBufferSwitchTimeInfo(ASIOTime* params, long doubleBufferIndex, ASIOBool directProcess);

					// safety function to make sure all is well before attempting any operations
					void CheckInitialised();

					// the input channels
					array<Channel^>^ _inputChannels;

					// the output channels
					array<Channel^>^ _outputChannels;

					// C++ likes 'non-trivial' events
					EventHandler^ _bufferUpdateEvent;

					// return the instance of currently selected driver
					static property AsioDriver^ Instance { AsioDriver^ get(); }


					// returns the installed drivers
					static property array<InstalledDriver^>^ InstalledDrivers	{ array<InstalledDriver^>^ get(); }

					// select and initialise driver
					static AsioDriver^ SelectDriver(InstalledDriver^ installedDriver);

					// basic information properties
					property int					Version					{ int get(); }
					property String^				DriverName				{ String^ get(); }
					property String^				ErrorMessage			{ String^ get(); }
					property int					NumberInputChannels		{ int get(); }
					property int					NumberOutputChannels	{ int get(); }
					property BufferSize^			BufferSizex				{ BufferSize^ get(); }
					property double					SampleRate				{ double get();}
					property array<Channel^>^		InputChannels			{ array<Channel^>^ get(); }
					property array<Channel^>^		OutputChannels			{ array<Channel^>^ get(); }

					// basic methods
					void Start();
					void Stop();
					void ShowControlPanel();
					void CreateBuffers(bool useMaxBufferSize);
					void DisposeBuffers();
					void Release();
					void SetSampleRate(double rate);

					// and the buffer update event - bit strange the way this works in c++
					event EventHandler^ BufferUpdate
						void add(EventHandler^ e) { _bufferUpdateEvent += e; }
						void remove(EventHandler^ e) { _bufferUpdateEvent -= e; }

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About the Author

Rob Philpott
United Kingdom United Kingdom
I am a .NET architect/developer based in London working mostly on financial trading systems. My love of computers started at an early age with BASIC on a 3KB VIC20 and progressed onto a 32KB BBC Micro using BASIC and 6502 assembly language. From there I moved on to the blisteringly fast Acorn Archimedes using BASIC and ARM assembly.

I started developing with C++ since 1990, where it was introduced to me in my first year studying for a Computer Science degree at the University of Nottingham. I started professionally with Visual C++ version 1.51 in 1993.

I moved over to C# and .NET in early 2004 after a long period of denial that anything could improve upon C++.

Recently I did a bit of work in my old language of C++ and I now realise that frankly, it's a total pain in the arse.

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