6 Feb
2011
6 Feb
'11
8:48 p.m.
Am 04.02.2011 02:11, schrieb Niels Mayer:
On Wed, Feb 2, 2011 at 12:48 PM, Stefan Kost
<ensonic(a)hora-obscura.de
<mailto:ensonic@hora-obscura.de>> wrote:
Sorry for the very late reply. One thing to mention is that the CPU load for
pulse is going wown quite a bit when plugin headphones. Otherwise it runs some
extra processing needed to accomodate the speakers.
Since there is a lot of extra audio processing going on, would employing a
library like "nova-simd", announced below, help out with the situation -- e.g.
writing the handset speaker-equalization and some of the audio mixing
functionality using more efficient instructions? What looks interesting is the
claimed support for both ARM Neon, Altivec, and Atom: See
http://tim.klingt.org/code/projects/nova-simd/repository and forwarded
announcement below.
Interesting. Need to take a closer look. Please note that pulseaudio is written
in C. Orc might be better suitable for PA also.
Stefan
....
Regarding pulseaudio,
in
http://code.google.com/p/ytd-meego/wiki/CitizenJournalismWithYoutubeDirectF…
-- Note
all the "ins and outs" back and forth between kernel and user space.
Architecturally, the system seems inverted, especially since you have to go back
out to ALSA for bluetooth. Why not keep it all in kernel space??
Or better yet: employ analog mixing and multiple DAC's -- only one or two
needing to be "hi-fi" and the others for notifications and telephony can be
quite cheap low-rate, low-accuracy DAC's and ADC's. Yes analog mixing and
routing is hard to do in a mixed signal environment; but is the power
consumption of a few DACs and op-amps even close to that of needing a fraction
of the CPU running constantly just to do what a few resistors and an op-amp can
do? To say nothing about the potential sound quality improvement of not needing
to resample any of the mixed outputs, nor worry about synchronizing or locking
rates between different subsystems, and all the other benefits of analog
summing: http://emusician.com/mag/emusic_sum_tracks/ ... (hopefully the
flamewars that will ensue about this controversial topic will cancel out the
flamewars on pulseaudio :-) ) .
What I'm proposing for the low-power/handset world isn't that far off from the
audio system needed back when CPU's had computational power that made digital
mixing for notifications, telephony, or music playback unthinkable: the analog
mixing built into the http://en.wikipedia.org/wiki/AC'97
<http://en.wikipedia.org/wiki/AC'97> spec (and associated hardware), but
updated
for the handset world. I'm sure that's not going to happen anytime soon, but I
can dream?
...........
Anyways, here's the announcement:
http://music.columbia.edu/pipermail/andraudio/2011-February/000098.html
......................
[andraudio] nova-simd suite updated for arm neon
Dan Stowell
Thu Feb 3 04:48:36 EST 2011
Hi -
"nova-simd" is a C++ header-only template library for taking advantage
of SIMD instructions in the kind of DSP processes used in audio
processing (i.e. not just basic stuff like vectorised mul+add and loop
unrolling, but also some more audio-specific things like ramps,
distortions).
It's created by Tim Blechmann and it lives here:
http://tim.klingt.org/code/projects/nova-simd/repository
It was originally implemented for SSE and SSE2 - we use it in
SuperCollider and it gives us massive performance improvements on
intel chips. We've just added NEON (and Altivec) implementations too,
so we should be able to boost performance on android and ios.
The ARM NEON support is new and doesn't yet implement all the
speedups, but should be useful for anyone wanting to implement C++ DSP
for Android devices with SIMD speedups - especially if you're thinking
about cross-platform code since the API is implemented for other chips
too.
Dan
.................
Niels
http://nielsmayer.com