ewmailing at gmail.com
Fri Mar 2 17:08:17 PST 2012
>From Section: 5.3.4. Specifying Buffer Content
Buffers containing audio data with more than one channel will be
played without 3D spatialization features – these formats are normally
used for background music.
On 3/2/12, Jason Daly <jdaly at ist.ucf.edu> wrote:
> I guess I thought that it had been specified (i.e.: in the spec) that
> multichannel sources wouldn't ever be spatialized, but I can't seem to
> find that now. Traditionally, at least the Loki and Creative
> implementations followed this concept. Only mono sources were
> spatialized and stereo/multichannel sources were passed through.
> Is this basically intended to formalize that idea?
> On 03/02/2012 10:12 AM, Chris Robinson wrote:
>> This and the loopback extension are what I'm hoping to have done before
>> releasing OpenAL Soft 1.14.
>> OpenAL Soft somewhat recently got support for HRTF filters for when using
>> headphones, however some stereo audio tracks may already be designed to
>> with headphones which makes it not sound as good when fed through HRTF
>> filters. Something like this was requested as a way to let such audio pass
>> through to the output without going through spatialization.
>> Chris Robinson
>> Chris Robinson (chris.kcat 'at' gmail.com)
>> This extension is written against the OpenAL 1.1 specification.
>> This extension allows a multi-channel source to play without
>> output speakers. By default, OpenAL requires buffer channels to be
>> mixed to the output channel configuration, possibly using HRTF
>> to give a sense of speakers that may not be physically present.
>> audio tracks are authored with their own spatialization effects,
>> where the
>> AL's spatialization methods can cause a notable decrease in audio
>> This extension provides a mechanism for applications to specify
>> audio should be filtered according to the AL's channel spatialization
>> methods for multi-channel buffers.
>> Q: Should this be a buffer property or source property?
>> A: Source property. This gives more flexibility to the app to decide
>> whether some piece of audio should be filtered or not.
>> Q: Should this work on mono (3D) sources?
>> A: No. Besides most people not having a mono speaker, or possibly
>> even a
>> front-center speaker, its main intent is for stereo tracks that
>> spatialization effects pre-applied.
>> Q: Are environmental effects, provided by EFX for example, still
>> A: Yes. There's no compelling reason to disable them, particularly
>> the application has to enable them on a per-source basis in the
>> New Procedures and Functions
>> New Tokens
>> Accepted by the<paramName> parameter of alSourcei, alSourceiv,
>> alGetSourcei, and alGetSourceiv:
>> AL_DIRECT_CHANNELS_SOFT 0x1033
>> Additions to Specification
>> Append to Section 4.3.2, Source Attributes
>> Table 4.x Channel Virtualization
>> Name Signature Values Default
>> ------------------------- --------- ------------------- ----------
>> AL_DIRECT_CHANNELS_SOFT i, iv AL_TRUE, AL_FALSE AL_FALSE
>> AL_DIRECT_CHANNELS_SOFT set to AL_TRUE indicates the audio channels
>> do not
>> go through virtualization or spatialization and plays directly on the
>> matching output channel if it exists, otherwise it is dropped.
>> only when playing non-mono buffers.
>> Openal-devel mailing list
>> Openal-devel at opensource.creative.com
> Openal-devel mailing list
> Openal-devel at opensource.creative.com
Beginning iPhone Games Development
More information about the Openal-devel