The ALSA ideology

OSS specific Linux discussion (x86/amd64)

Moderators: hannu, dev, cesium

igorzwx
Known Member
Posts: 1256
Joined: Sun Jun 28, 2009 9:31 pm

The ALSA ideology

Postby igorzwx » Thu Sep 03, 2015 3:08 pm

Since ALSA users are trying to spam the OSS4 forum with ALSA ideology, it might be necessary to explain what ALSA ideology is.

ALSA users seem to believe that "sample rate" is frequency; although, of course, they are different things, as the names suggest.

The quality of digital audio depends on resolution (and some other things). It depends on resolution simply because it is digital.
The resolution of digital audio (PCM waves) is defined by "sample rate" and "bit depth"
_https://en.wikipedia.org/wiki/Audio_bit_depth
Low sample rates mean low quality of digital audio.

Since human being cannot hear digital audio, it should be converted to analog signal. Analog signal is a continuous signal, by definition. It has an infinite sample rate and infinite bit depth, because it is continuous.

Human beings can hear analog signals, but this does not mean that they can hear infinite frequencies. It might be stating the obvious, but "infinite sample rate" does not mean "infinite frequency", simply because "sample rate" does not mean "frequency".

EXAMPLE: The sine wave _https://en.wikipedia.org/wiki/Sine_wave

Imagine a very simple analogue signal:

y(t) = A sin(2πft)

A is the amplitude of the analogue signal.
f is the frequency of the analogue signal.
t is time.
π is a mathematical constant _https://en.wikipedia.org/wiki/Pi

This sine wave defines an analogue signal of a certain frequency.
Let us take f = 440Hz. This frequency should be audible, because the "standard range of audible frequencies is 20 to 20,000 Hz"
_https://en.wikipedia.org/wiki/Audio_frequency

Since analogue signal is a continuous signal (by definition), and sine is a continuous function (by definition), it has an infinite sample rate and infinite bit depth.

To summarize: The analogue signal of 440Hz has an infinite sample rate and infinite bit depth. It is audible for human beings.

The "digital signal" of 440Hz is a discrete approximation of the sine wave of 440Hz. The exactitude of discrete approximation depends on resolution (that is, sample rate and bit depth). The difference between the sine wave and a discrete approximation of sine wave is distortion (by definition). Such distortions are usually amplified when "digital signals" are converted to "analogue signals" by your soundcard.

To minimize audible distortions in "analog audio", you have to use "digital audio" of high resolution. That is why audiophiles tend to use HiRes Flacs and DXD waves, instead of "digital crap" of 48kHz sample rate.

The problem of ALSA is that high sample rates do not make any difference with ALSA. A digital audio of high quality (high sample rate) may sound exactly like digital audio of low quality (low sample rate). It may sound even worse, if ALSA downsamples everything to 48kHz with a low quality (fast) resampler
_http://www.opensound.com/forum/viewtopic.php?f=3&t=5807&start=105#p21347

To explain this unpleasant fact, the ALSA developers created a special theory about the "myth of the golden ear":

The Myth of the Golden Ear
Some audiophiles love to obsess over specs and are convinced that, yes, they too can hear super-high frequencies just like bats, and the super-low frequencies just like whatever animal hears super-low frequencies...
Carla Schroder, The Book of Audacity (2011), p.333.


This theory states that ALSA users do not hear the difference between HiRes audio of 192kHz sample rate and "digital crap" of 48kHz sample rate, because human beings cannot hear frequencies above 20kHz, and also because they do not have speakers or headphones which can produce such frequencies like 96kHz.

This statement can be turn into a "self-evident truth" by dropping some words, for example:
ALSA users do not hear the difference between HiRes audio of 192kHz and LowRes audio of 48kHz, because human beings cannot hear above 20kHz.
Now, 192kHz can be confused with frequency, and the theory can be consumed as "absolute truth".

Such theories tend to be called ideologies. The purpose of ideology is to fool the stupid, to make them feel happy with any crap which they have to consume.

The ideologies of this sort are usually created when certain problems are very difficult to fix, or impossible to fix. It might be obvious that ALSA is fundamentally wrong by design, and, therefore, some problems cannot be fixed.

The arrival of DXD audio format 352kHz 24bit spells disaster for ALSA and threatens the job security of ALSA developers. Therefore, they may try to undermine competing sound systems through the help of propaganda and disinformation.

Digital eXtreme Definition [DXD] is a professional audio format that brings "analogue" qualities in 32 bit floating point at 352.8 kHz. DXD preserves 11.2896 Mbit/s (4 times the data of DSD).
_http://www.2l.no/pages/about.html
See also: _https://en.wikipedia.org/wiki/Digital_eXtreme_Definition


Head-Fi.org - Headphone forums and reviews for audiophiles
_http://www.head-fi.org/

Morten Lindberg's DXD waves 352kHz/24bit can be downloaded here: _http://www.2l.no/hires/index.html

Morten Lindberg 2L - Norway
_http://www.merging.com/news/use-cases/morten-linderg-2l-norway

DXD waves and DXD FLACs 352kHz/24bit for audiophiles can be purchased on HDtracks _https://en.wikipedia.org/wiki/HDtracks

DXD waves can be played with Petrov's pcm_play
_http://www.opensound.com/forum/viewtopic.php?f=3&t=5789
_http://www.opensound.com/forum/viewtopic.php?f=3&t=5792
_http://www.opensound.com/forum/viewtopic.php?f=3&t=5795

Return to “Linux”

Who is online

Users browsing this forum: No registered users and 3 guests