On 2015-03-31 13:31, Ricard Wanderlof wrote:
On Tue, 31 Mar 2015, David Henningsson wrote:
On 2015-03-31 12:06, Nikita N. wrote:
If you have any concrete examples (alsa-info please!) of speakers that can be burned out, and you know a maximum speaker volume where this
As we said, that is not our bug, we are not audio experts, nor any of us is interested in audio matters.
Here's my suggestion how to move forward on this:
- Gather consensus that limit the maximum volume on internal speakers
is the right way forward. Takashi, Clemens, anyone against that strategy?
- From the person with the hardware, we will need alsa-info (
https://wiki.ubuntu.com/Audio/AlsaInfo ), and also the max volume where this does not happen. Is -6 dB good enough? -12 dB? I don't know - this is something someone with the hardware must tell us, it cannot simply be guessed.
- I or someone else can write a kernel patch that limits the maximum
volume of the speakers to the amount deducted from point 2). Considering that we're actually dealing with hardware breakage, this should be sent to stable as well. Then no userspace application can set the volume higher than our limit.
While we could technically limit the output level in a driver, the output level at which the speakers get damaged must surely depend not only on the codec but also on the particular analog output stage driving the speakers (assuming it's not built into the codec), the speakers themselves, as well as any other hardware on the board, for instance coupling capacitors, or potential overload protection circuitry, most of which are components which we cannot identify in the driver.
My point is that unless this is a problem with a very specific hardware, there's no way the software can actually know what a "dangerous" level would be, and hence we cannot limit it in software. What is a "dangerous" level in one setup could be an unusably low level in another setup, where both setups look identical from a driver point of view.
I'm thinking that any limits must be dependent on a particular hardware setup, which means in order to be successful, we would have to extract some sort of model name of the system we're actually running on, to be compared against some sort of graylist. With the proliferation of model names of PC:s, such a list would be sketchy at best.
Yes, this is a problem with very specific hardware, and that's why I asked for alsa-info - part of what we get from that is somewhat of a unique model-ID (in the form of a PCI SSID).