Subject: [linux-audio-dev] Re: Alsamixer: Dangerous Design!!!!
From: Juhana Sadeharju (kouhia_AT_nic.funet.fi)
Date: Wed May 03 2000 - 19:11:11 EEST
I added Linux Audio Dev list.
Short summary: I found out that Alsamixer puts master volume
to maximum when "Home" key is pressed. I find myself very lucky not
accidentally doing so because the produced volume is dangerous. I have
rather common Sennheiser headphones + SB16 audio card.
While I modified my Alsamixer for having maximum master level 50%,
that doesn't make others life any safer. I have proposed a couple of
safety features for both Alsa drivers and audio software.
The maximum hardware master level lock should be in the Alsa driver because
it cannot be assumed that your Alsamixer is the only which alters the master
volume. This lock would be adjustable from software but the root could set
it unadjustable.
The lock would be on by default because we should think __the worst cases__.
After the hardware master volume level is set to some non-damaging level,
either Alsa or audio software uses a software volume for additional
volumes. (For hearing low volume signals, software volume is anyway
better than the hardware volume.)
If really interested, check the Alsa-devel mails where I describe
why it is not enough "just to be careful".
>From: Jeremy A Erwin <jerwin_AT_osf1.gmu.edu>
>
>This may be more difficult than you realise. It sound similar to the
>compression algorithms used AC3 to maintain a constant volume level across
>programs. I'm not at all sure how this may work.
It is not about that. Alsa driver should support the feature which forbits
any attempt to turn the master volume louder. Plain simple.
>This is diffucult to do properly. After all, most hearing damage is caused
>not be exposure to transients, but to prolonged exposure to loud
>noises. Ideally, such calibration is best done with a sound pressure
>meter, and not with a subjective "is it too loud" test. Most portable
>audio products recomend turning the volume to nil, and adjusting
>upward. How would you calibrate the "safe volume" level for the 1812
>overture?
This has nothing to with psychoacoustic. We just output loudest signals
and adjust the level to what sounds okay. I prefer volumes which are
a far away from what most people may tolerate. After setting this level
I know the system doesn't produce any louder signal, and that is the
main point, not finding a psychoacoustically maximum level for all music
types or such.
>Again, this depends on the source material... Reducing the volume may
>cause a user not to hear material on the source.
The software volume is for bringing low level signals up. There is no need
to raise the hardware volume for hearing those low level signals. This
software volume could be inside the Alsa driver as well and not only in
audio software.
A reasonable hardware volume is good enough for your 1812 Overture.
If a song has entirely low volume, it can be corrected with software
volume without distortion.
>Perhaps one can disable auto repeat in mixer applications...
Sure anything can be done but people do use different programs
and not all programs has such features.
I'm planning to write a guides for writing a quality audio software
but nothing really helps but put the limits to Alsa. When they are
put to Alsa, user would be safe from badly designed software.
>If you use headphones on a regular basis, and are concerned about audio
>fidelity, an external amp may prove to be a better choice. Many external
>amplifiers include limiting circuitry on headphone outputs. In addition
>many external ampliers have the advantage of higher fidelity.
Don't talk about me only. Talk about hundret thousands of other Linux users.
Talk about Joe Averages who has no idea about good headphones and extra
audio hardware.
It is nonsense to talk about that people should spend money to proper
hardware because millions of people have no idea about these issues.
They buy what a shop clerk gives to them.
>I agree that hearing damage is a serious problem. However implementing a
>solution in software has its disadvantages, and may lead a user of alsa
>software into complacency. If limiting circuitry is implemented within
>alsa, but does not truly prevent long term hearing damage, the designers
>of alsa might be morally (but not necessarily legally or
>financially) responsible.
Nonsense. Are Alsa developers now any less morally responsible if somebody
hits the "Home" button accidentally and gets 300 dB to ears?
Either we set up new safety rules or then not! I think it is better to
set up them than not. Fully motivated safety system doesn't cause any
complaints. If you want remove the safety, then it needs an extra work
but that is not a place for complaints __in this context__.
We can vote on this if needed.
I'm still waiting for some official comments on these matters.
Juhana
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