Re: HAL user-land audio driver
Re: HAL user-land audio driver
- Subject: Re: HAL user-land audio driver
- From: "Mikael Hakman" <email@hidden>
- Date: Wed, 2 Apr 2008 13:13:09 +0200
- Organization: Datakonsulten AB
Many thanks Jeff! I can confirm that the entity which handles the volume
up/down bumping divides 0.0 - 1.0 range into 16 steps (number of dots shown
on volume popup when using remote control). It then increases/decreases the
volume level by one step for each press on +/- button on remote control. If
actual device dB range is e.g. -96 - 0.0 (16 bit range) and scalar values
map linearly to dB then each step corresponds to 6 dB, i.e. 1 bit - a device
using 32 bit integer format internally could simply bit-shift the values.
You mentioned before that there are routines in Core Audio that can provide
various mappings from scalar value to dB. What are their names? I would need
a mapping that better corresponds to human perception of loudness than
linear dB mapping does. My own experience tells me that the steps at low
volume should be larger and the steps at high volume should be smaller. What
mapping is used by built-in analog audio output? Its step at low end is
almost twice that of at high end.
Is it possible to request larger number of steps than 16 to be used by
remote control of volume?
TIA
On March 31, 2008 11:07 PM, Jeff Moore wrote:
The entity that handles the volume up/down bumping just sees a control
whose range goes from 0.0 to 1.0. It divvies that up by the number of
steps it needs to support and increments by that much. I don't believe
that this code bothers to look at the dB range of the control at all.
On Mar 31, 2008, at 4:16 AM, Mikael Hakman wrote:
On to the next question. When using Apple IR remote to control output
volume level, the system increases/decreases the level for each press on
+/- buttons on the remote. What is the algorithm used by the system in
order to compute how much to increase/decrease the volume level for each
press, as related to decibel range reported by the device, and perhaps
also to conversions between "scalar" and decibel level values provided
by the same? I'm trying to establish such a mapping that the
increase/decrease done for each press would agree with what is observed
for the other devices.
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