Volume II in Vista: volume types in Windows Vista

Original article: http://blogs.msdn.com/larryosterman/archive/2007/04/04/volume-in-windows-vista-part-2-types-of-volume-in-windows-vista.aspx
Author: Larry osterm
Translation: Tony Qu

Yesterday, I gave a general introduction to volume control. Today I will explain in detail.

In Vista, there are four different volume control methods for any audio stream:
1. Stream volume)
2. Simple volume)
3. Channel volume)
4. endpoint volume)

Since each method is a gain stage, each type can be added to the audio input sample to generate the final audio output stream.

I plan to take a picture from the "audio in Vista-big image" of last year)

Each wasapi instance in the figure represents an audio stream, which is merged in the audio synthesizer (mixer) and "streaming" the audio driver. The stream volume, simple volume, and channel volume are achieved by inserting an APO into an independent audio stream, the endpoint volume is to add an APO behind the synthesizer or use hardware volume control to process it, depending on the features of your audio solution.

So what is the relationship between these different audio controls?

First, let's talk about the stream volume. The stream volume is a multi-channel volume that acts on each audio stream and can be used by applications.ProgramImplement relatively simple 3D effects (use multi-channel stream volume control to simulate a position change after an active ball is played ). You can allow applications to control the volume of an independent audio stream, but this demand is relatively small.

Next is the channel volume. The channel volume is the volume of the audio session (Session), used to control the volume of all audio streams in the entire session (if you still remember the "big picture" post, A session contains many audio streams ). Channel volume exists because of the waveoutsetvolume API-because the waveform volume is a multi-channel (STEREO) volume, we must simulate one in wasapi. Similarly, this volume is rarely used-the channel volume is usually changed only when the system installation task (space correction) is run from the control panel, therefore, this setting affects all applications, not just specific applications ).

Then the simple volume is used. Simple volume is the volume of the audio Session, which is used to control the volume of all audio streams throughout the session. It is a unified volume that is evenly applied to all channels. This is also the way we want most applications to use volume control-because it provides a simple way to control the volume and mute state of applications, this method is sufficient for most applications. This volume is actually the volume Slider of each application displayed in the Vista sound mixer.

Logically, you can apply the above three volumes (but they are not actually applied at the same time) to create the final volume for each audio stream.

Finally, let's talk about the terminal volume. As I have mentioned before, the endpoint volume represents the master output. It acts on the final merged audio stream and can control the base volume of a specific endpoint.