At Thu, 8 Mar 2012 17:30:02 +0100, Elimar Riesebieter wrote:
severity 663090 normal forwarded 663090 alsa-devel@alsa-project.org thanks
- Adam Lee adam8157@gmail.com [2012-03-08 20:36 +0800]:
Package: alsa-utils Version: 1.0.25-1 Severity: important
db is not linear, but amixer believe it is.
"amixer get Master" says "Limits: Playback 0 - 74", then everytime I run "amixer -q sset Master 10%-", there is 8db dec.
For example, at first Master is 100% and 0db, both alsamixer and amixer think it is, and after I run "amixer -q sset Master 10%-", both alsamixer and amixer says Master is -8.00db, but alsamixer says it is 72%, amixer says it is 89%.
alsamixer is right, amixer calc and set wrongly.
No, both are correct. You are dreaming too much on the world unified percentage representation :)
The percentage in amixer has nothing to do with dB level. It's just the percentage of the raw value range of that mixer element. Thus showing 89% is correct. It's 10% down from 100% (1% is because of the resolution of the raw values).
Now, alsamixer shows the percentage in a different way. It's explained well in the source code (alsamixer/volume_mapping.c), but not mentioned in the man page, unfortunately.
* The mapping is designed so that the position in the interval is proportional * to the volume as a human ear would perceive it (i.e., the position is the * cubic root of the linear sample multiplication factor). For controls with * a small range (24 dB or less), the mapping is linear in the dB values so * that each step has the same size visually. Only for controls without dB * information, a linear mapping of the hardware volume register values is used * (this is the same algorithm as used in the old alsamixer).
The percentage representation in alsamixer corresponds to this mapping, thus it's neither dB nor linear percent.
Takashi
Several months ago, they both right, and I upgraded, and amixer messed up. Please fix it. Thank you.
FYI, my hardware is: "HDA-Intel" "Conexant CX20585" "HDA:14f15069,17aa214c,00100302 HDA:14f12c06,17aa2122,00100000" "0x17aa" "0x215e"
-- System Information: Debian Release: wheezy/sid APT prefers unstable APT policy: (500, 'unstable') Architecture: amd64 (x86_64)
Kernel: Linux 3.2.0-1-amd64 (SMP w/4 CPU cores) Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash
Versions of packages alsa-utils depends on: ii dialog 1.1-20120215-1 ii libasound2 1.0.25-2 ii libc6 2.13-27 ii libncursesw5 5.9-4 ii libsamplerate0 0.1.8-3 ii libtinfo5 5.9-4 ii linux-sound-base 1.0.23+dfsg-4 ii lsb-base 3.2+Debian29 ii module-init-tools 6-1 ii whiptail 0.52.14-8
Versions of packages alsa-utils recommends: ii alsa-base 1.0.23+dfsg-4 ii pciutils 1:3.1.8-2
alsa-utils suggests no packages.
-- no debconf information
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