mirror of
https://github.com/ivabus/speakersafetyd
synced 2024-11-22 16:25:06 +03:00
61 lines
3.6 KiB
Markdown
61 lines
3.6 KiB
Markdown
## speakersafetyd - a software Smart Amp implementation
|
|
speakersafetyd is a userspace daemon written in Rust that implements an
|
|
analogue of the Texas Instruments Smart Amp speaker protection model.
|
|
|
|
Apple Silicon Macs mostly use the Texas Instruments TAS2764 amp chip (codec
|
|
in ALSA parlance), which provides sense lines for the voltage and current across
|
|
the voice coil of the connected speaker. These codecs are designed to be used
|
|
in embedded applications where device firmware takes this information and uses
|
|
it to protect the speaker from damage. Apple instead implement this as machine-specific
|
|
plugins to the userspace half of CoreAudio. An increasing number of other
|
|
vendors in both the desktop and embedded/Android worlds are choosing to go down a similar
|
|
route, folding this functionality into proprietary driver/userspace blobs that usually
|
|
also bundle niceties like EQ (we have a solution for this too, see [asahi-audio](https://github.com/AsahiLinux/asahi-audio)).
|
|
This puts users at serious risk of permanently destroying their expensive devices if they choose
|
|
to run custom software, such as Asahi Linux or an Open Source Android ROM.
|
|
|
|
speakersafetyd is the first (as far as we know) FOSS implementation of a speaker
|
|
protection model. It solves the problem described above by allowing parties interested
|
|
in compatible devices to quickly and easily implement a speaker protection model for those
|
|
devices. Only Apple Silicon Macs under Linux are currently supported,
|
|
however the model applies to all loudspeakers. The daemon itself should be easy enough to
|
|
adapt for any device that provides V/ISENSE data in a manner similar to TAS2764.
|
|
|
|
### Dependencies
|
|
* Rust stable
|
|
* alsa-lib
|
|
* An Apple Silicon Mac running Asahi Linux
|
|
|
|
### Some background on Smart Amps
|
|
The cheap component speaker elements used in modern devices like
|
|
Bluetooth speakers, TVs, laptops, etc. are very fragile. In order
|
|
to eke the highest possible sound quality out of them, they need to be
|
|
driven *hard*. This leaves us with a dilemma - how do we drive these
|
|
speakers hard enoguh to get a loud, high-quality output but not hard
|
|
enough to destroy them?
|
|
|
|
A speaker's electromechanical characteristics can be modelled
|
|
and boiled down to a set of parameters - the Thiele/Small Parameters.
|
|
These can be used to predict what the speaker will do with certain
|
|
inputs. When we add measured properties like the time constant of
|
|
the speaker's voice coil's and magnet's temperature curve, we can
|
|
accurately model a speaker's temperature for any given voltage/current
|
|
across the coil. When the speaker is getting too hot, we just reduce the
|
|
power going to it until it cools down.
|
|
|
|
This lets us fearlessly drive the speakers as hard as they physically can
|
|
be without being permanently damaged. This is extremely useful, as without it
|
|
the output level on these devices would have to be hard limited to a very low
|
|
level that is known to be safe for the worst possible input. Instead, we can
|
|
simply duck the output in those cases and allow the speakers to operate at
|
|
full power where possible.
|
|
|
|
Many integrated amplifier chips implement this functionality in hardware, as well
|
|
as additional advanced DSP features like compressors and limiters. Texas Instruments
|
|
call their implementation "Smart Amp." Integrators need only communicate the parameter set
|
|
to the chip for the speaker it is connected to, and it does the rest. Many do not however,
|
|
and instead only provide facilities for measuring the voltage and current across the speaker's
|
|
voice coil. It is up to the implementer to capture this data and do something with it.
|
|
|
|
speakersafetyd is (as far as we know) the first and only FOSS implementation of the
|
|
Smart Amp protection model.
|