finally usb audio problems affecting the Pi, have been solved! For those of you seeking a Raspberry Pi Usb Audio fix, you’re in the right place!  I was compulsively lurking this thread hoping that the foundation would eventually find a fix for the usb issue. What was it?

Well, to make it simple, when the usb bus of the pi was receiving lot of i\o requests, it cannot satisfy them all, and as a result part of the data travelling trough usb was lost. So, while communicating with a usb dac , if the file being played was more than 44/16 the usb bus was overwhelmed and some parts of the data (packets, jargon comes in finally) was lost. If you google for packet loss, you can figure out what was happening.

I’ve been investigating a lot on the matter, hoping to find a Raspberry Pi usb audio fix , tried almost everything. But this was in the hands of the foundation, since there is no extensive documentation available.

Finally, the Raspberry Pi usb Audio Fix came on Thu May 09, 2013 9:19 am, from gsh (which has my imperiture gratitude)

Basically, this updates some part of the pi firmware and kernel, via rpi-update (this is an experimental branch you won’t find on the master branch of rpi-update by hexxeh 

For those of you on RaspyFi, update is hassle free since you already have rpi-update up and running. Just do this to enable the Raspberry Pi Usb Audio Fix:

sudo apt-get install git-core binutils

sudo BRANCH=fiq_split rpi-update

Let it run, it will need almost 20 minutes to complete. In case you’re receiving some errors, just retry. Sometimes the git servers are not able to face the requests of thousands users simoultaneusly.

Once it’s done, and you’re not getting any error, just reboot.

Now, it’s time to enable bit perfect playback on RaspyFi via mpd.conf

sudo nano /etc/mpd.conf

the line:

format “44100:16:2″ # optional

becomes

#format “44100:16:2″ # optional

ctrl + x to save.

Now, we’ll restart mpd:

sudo /etc/init.d/mpd restart

Now, play and enjoy! Files >44/16 will be played without glitches, and I hope that async dacs will work flawlessly as well! I cannot confirm this by now since I don’t have any async to the test this Raspberry Pi usb audio fix for them… But please let me know via comments below.

To check if your Pi now resides in Bit Perfect heaven just type, while playing:

cat /proc/asound/card0/pcm0p/sub0/hw_params

The output will show you current bit rate and bit depth, that should be the same as the file. Please note that if a bit rate/bit depth is not supported by your dac, mpd will automatically resample it to  the nearest supported one.

Here, an example (showing different bitrates/bitdepths, with perfect sound)

Raspberry Pi in bit perfect mode

Obviously, this raspberry pi usb audio fix will be implemented and working out of the box in next Release of RaspyFi, which is in its final stage of development.

This raspberry pi audio fix, also can be excecuted on plain Raspbian and all the other distros out there. Just type that:

sudo apt-get install git-core
sudo wget http://goo.gl/1BOfJ -O /usr/bin/rpi-update && sudo chmod +x /usr/bin/rpi-update
sudo BRANCH=fiq_split rpi-update

Et voilà, you’re done! Please let me know if it works for you, and if you got some troubles doing it !

UPDATE FOR SAMBA USERS

As suggested by Klinkt Beter and Carlo Bernardini this fixes the samba issues for async dac users. With my new xmos to i2s dac  and this fix I don’t have any stuttering at 24/96 , some reports this works well with 24/192 as well. So edit /etc/auto.nas as follows:

Nas    -fstype=cifs,file_mode=0777,dir_mode=0777,iocharset=utf8,sec=ntlm,rsize=2048,wsize=4096,cache=strict,username=pi,password=    ://192.168.nasip/sharename

L'articolo Raspberry Pi Usb Audio fix sembra essere il primo su RaspyFi.

Is my power supply good enough? 

Terrible drama then, desperation, no certainesses, no peace. Then he will start to browse and google compulsively, ask in forums, call his mom, loose hairs etc etc.

Well, at this point, there is only one thing you can do. Get a better one. So, for those of you in these miserable condition, here’s a tip on how to choose wisely a good power supply for Raspberry Pi.

Let’s introduce what are we talking about

Why Power supply is so important? Trivially speaking, we can say that our fancy audio\electronic gizmos work with electricity. And, the better and the most stable electricity we can give to them, the better they will work. This comes to an extreme importance in Audio, but can be true also for all kind of electrical equipment.  Let’s see why:
Most circuits works with DC. DC is direct current, which is:

used to refer to power systems that use only one polarity of voltage or current, and to refer to the constant, zero-frequency, or slowly varying local mean value of a voltage or current.For example, the voltage across a DC voltage source is constant as is the current through a DC current source. The DC solution of an electric circuit is the solution where all voltages and currents are constant. It can be shown that any stationary voltage or current waveform can be decomposed into a sum of a DC component and a zero-mean time-varying component; the DC component is defined to be the expected value, or the average value of the voltage or current over all time.

 

http://en.wikipedia.org/wiki/Direct_current

 

Usually, direct current is obtained by rectifying AC (Alternated current), which flows by our wall socket. A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction.
This is the first quality sensible step that our electrons are faced to do. In these process, it could happen that some residuals of the AC’s typical voltage oscillations will remain in the DC stream, producing some kind of “fluctuation” from our desired voltage.
This phenomenon is called ripple:

The most common meaning of ripple in electrical science is the small unwanted residual periodic variation of the direct current (dc) output of a power supply which has been derived from analternating current (ac) source. This ripple is due to incomplete suppression of the alternating waveform within the power supply.

This could be better described with picture below:

As you can see, by simply rectifiying AC (first scenario) we will end with lot of oscillations in voltage, this will result in poor performance (in audio domains). As for our Raspberry Pi, a power supply with high ripple will result in malfunctions, sd card corruptions etc etc.
In the second picture, we’ll see how a filter applied to our power supply can dramatically reduce ripple. This more stable voltage will result in a HUGE improvement in audio applications, and for our raspberry Pi will mean better working conditions.
Those of you who already know about this matter could find this explanation extremely reductive and simple. I know it is, but I’m trying to keep things simple.

So, what power supply should I choose? There are 2  main categories:

Linear power supplies

These are the type we discussed earlier, as you can see the first component (from left side) is a power trasformer, this transform the voltage from our wall socket to a desired one (let’s say 24 volts), passing this step the current is still alternated.
Then it passes trough some diodes (1,2,3,4), their function is to rectify current and make it dc. Passing this step our DC is very dirty, and that’s why there will be some filtering capacitors (C) to smooth it out and reduce ripple. This is a very simple schematic, but should give you the idea. Usually, where a given voltage with very low ripple is needed you’ll use also a voltage regulator. This component will reduce the imput voltage to a given one, and provide very low ripple output. Capacitors are often used to further smooth the output voltage, and their quality is hugely responsible of subsequent psu quality.
The main disadvantage of these kind of power supply is their efficiency. Lot of energy got wasted in this process (as heat, for example) and they usually drain lot more current than they put out.

Then, we’ll find

Switching power supply

A switched-mode power supply (switching-mode power supply, SMPS, or switcher) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a source, like mains power, to a load, such as a personal computer, while converting voltage and current characteristics. An SMPS is usually employed to efficiently provide a regulated output voltage, typically at a level different from the input voltage.

Unlike a linear power supply, the pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions (which minimizes wasted energy). Ideally, a switched-mode power supply dissipates no power. Voltage regulation is achieved by varying the ratio of on-to-off time.

So as you can understand, switching power supplies achieve the same result by turning on and off repeatedly (thousands of times per second) the electrical stream, resulting in better efficiency (no rectification, no voltage transformation, no voltage regulation). The main disadvantage are in terms of quality. Switching power supply usually have higher ripple than linear power supplies.

So now the choice is between quality and efficiency. Since our raspberry Pi will draw as much as 700 mA (current) at 5 ± 0,25 volts      (voltage) we should choose a psu which can output at least 1 amp (extra 300mA for connected devices such as DACs or usb keys), whith a voltage between 4,75 and 5,25 volts. Any different value from these will (and I mean, it will) result in SD Card corruption, especially if you decided to overclock your PI.
By choosing a linear power supply for Raspberry Pi, like

, you’re sure gettin highest quality power supply, but this will result in lot of enery wasted and a higher electricity bill (of course, relatively speaking) (please also mind that you should change the DC jack in favour of a microUSB plug). By the other hand a switched mode power supply for Raspberry Pi like this (or

if you’re on the other side of the Atlantic)  will  be an energy saving savy choice but quality wise, is the worst scenario you can get.

And after telling you all of this, I’ll let you cry in tears and desperately wating to know what to do by saying goodbye !

Next , will come a comparison of multiple power supply for Raspberry Pi, and a project of a custom power supply which will hopefully satisfy both quality and efficiency!

L'articolo Power Supply for Raspberry Pi, what you should know about sembra essere il primo su RaspyFi.

First, update to latest kernel and firmware. This brings minor usb optimizations, unfortunately the bugs affecting over 44,1 khrz playback are still present. The foundation reported to be working hard on the matter (they hired a specialist to solve the issue, at least that’s what i got…)

sudo apt-get install git-core
sudo wget http://goo.gl/1BOfJ -O /usr/bin/rpi-update && sudo chmod +x /usr/bin/rpi-update
sudo rpi-update

Then, we’ll strip down the distro. This aims basically to use less disk space, but less processes active (especially X graphic user interface) leave the pi arm cpu quieter. Some folks believe that less processes running= better sound. I am not one of those. I indeed can say that less cpu used= less power drain and more responsive system. This can indirectly improve playback quality, also for electrical inducion reasons. But my physics knowledge is not enough to explain clearly the reason why.

Sudo apt-get update

Getting a list of all packages installed give us an idea of what we can remove.

dpkg --get-selections

Let’s remove what we don’t mind to use

sudo apt-get remove aspell desktop-base desktop-file-utils dictionaries-common dillo fonts-droid fonts-freefont-ttf fontconfig fontconfig-config galculator gnome-icon-theme gnome-themes-standard gpicview gsettings-desktop-schemas gsfonts gsfonts-x11 hicolor-icon-theme leafpad lightdm lightdm-gtk-greeter lxappearance lxde lxde-common lxde-core lxde-icon-theme lxmenu-data midori mime-support openbox omxplayer penguinspuzzle x11-common wpagui python3 python3-minimal python-pygame x11-common

Python games? Glad to ask, but no.

sudo rm -rf python_games

Opt contains lot of heavy stuff, such like a damn 1080i video.

sudo rm -rf /opt/vc/src/hello_pi/hello_video/

Python, go away!

sudo apt-get remove `sudo dpkg --get-selections | grep -v "deinstall" | grep python | sed s/install//`

Removing gcc, we’ll install latest version later

sudo apt-get remove gcc-4.4-base:armhf gcc-4.5-base:armhf gcc-4.6-base:armhf

Clean unnecessary packages

sudo apt-get autoremove
sudo apt-get clean

Ok, now let’s update the software environment

sudo apt-get update
sudo apt-get upgrade

sudo apt-get clean

let’s check how much space did we free up:

df -h

Filesystem Size Used Avail Use% Mounted on
rootfs 1.8G 870M 804M 52% /
/dev/root 1.8G 870M 804M 52% /
devtmpfs 235M 0 235M 0% /dev
tmpfs 49M 252K 49M 1% /run
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 98M 0 98M 0% /run/shm
/dev/mmcblk0p1 56M 21M 36M 37% /boot
tmpfs 98M 0 98M 0% /tmp

870, could be worse

We don’t need swap. Do we?

sudo swapoff -a
cd /var
sudo dd if=/dev/zero of=swap bs=1M count=100

Now, we’ll install Mpd. We will now get and install the vanilla package, the one provided with debian. We will use this to get it’s infrastructure, and then we’ll install latest version from source.

sudo apt-get install mpd mpc

Now we install both prerequisites to compile mpd and mpd’s dependencies

sudo apt-get install aptitude wget binutils gcc make subversion autoconf automake autotools-dev libtool pkg-config build-essential libncurses5-dev libncursesw5-dev gcc libglib2.0-dev

sudo apt-get install libfaad2 libfaad-dev libflac8 libflac-dev libogg0 libogg-dev libvorbis0a libvorbis-dev libid3tag0 libid3tag0-dev libmad0 libmad0-dev libcue-dev libcue1 libasound2 libasound-dev libasound2-dev libao-dev libwavpack-dev libwavpack1 libsamplerate0 libsamplerate-dev libmikmod2-dev libmikmod2 libmikmod-dev libshout-dev libavformat-dev libavcodec-dev libavutil-dev libaudiofile-dev libcurl4-openssl-dev libmms-dev libmms0 libtwolame-dev libtwolame0 libmp3lame-dev git-core

Now, we clone the official mpd repo, in order to obtain and compile latest mpd version. As root:

sudo su
cd /home/pi
git clone git://git.musicpd.org/master/mpd.git

cd ./mpd

./autogen.sh

We then configure it to use few options, making mpd more lightweight.

./configure --disable-bzip2 --disable-iso9660 --disable-zzip --enable-id3 --disable-sqlite --enable-ffmpeg --enable-alsa --disable-wave-encoder --enable-pipe-output --enable-httpd-output --disable-recorder-output --disable-sndfile --enable-oss --enable-shout --disable-pulse --disable-ao --disable-mad --disable-inotify --disable-ipv6 --enable-curl --disable-mms --disable-wavpack --disable-lame-encoder --disable-twolame-encoder --enable-vorbis --enable-lsr --with-zeroconf=auto

make
make install
sudo su
/etc/init.d/mpd stop
echo DAEMON=/usr/local/bin/mpd >>/etc/default/mpd
/etc/init.d/mpd start
mkdir -p ~/.mpd/playlists

Now, we’ll start configuring mpd, editing the mpd.conf file

sudo nano /etc/mpd.conf

What interest us is:

#group "nogroup"

Becomes

group "audio"

Mpd will belong to “audio” group, which will be useful for setting mpd’s priorities.

Then

bind_to_address "localhost"

that will become

bind_to_address "any"

Activating auto-update by uncommenting following line, this will enable mpd to automatically update its music database when something new is added or removed.

#auto_update "yes"

Then

audio_output {
type "alsa"
name "My ALSA Device"
device "hw:0,0" # optional
format "44100:16:2" # optional
mixer_device "default" # optional
mixer_control "PCM" # optional
mixer_index "0" # optional

that will become

audio_output {
type "alsa"
name "USB Dac"
device "hw:0,0" # optional
format "44100:16:2" # optional
# mixer_device "default" # optional
# mixer_control "PCM" # optional
# mixer_index "0" # optional

Then we’ll uncomment the lines regarding the buffer

audio_buffer_size "2048"
buffer_before_play "10%"

Ctrl+ x to save, then y to confirm.

Now we assign to our usb dac the device number 0, which is the default for mpd and the mixer. We can do so by commenting out the line

options snd-usb-audio index=-2

in

sudo nano /etc/modprobe.d/alsa-base.conf

By doing so, RaspyFi will use as default the USB Dac. If a usb dac is not connected, then the default audio out will be the analog jack. Nasty!

Now, we create our music directories and mount points. We can use multiple directories, such a nas and a usb drive, by putting a shortcut in mpd default music directory.

mkdir /mnt/nas
chmod 777 /mnt/nas

Add the following line in /etc/fstab

nano /etc/fstab

//192.168.1.NasIP/YourShareName /mnt/nas cifs username=pi,password=,uid=mpd,file_mode=0644,dir_mode=0755,iocharset=utf8,rsize=130048,wsize=4096 0 0

This will automatically mount our samba share on /mnt/nas.

Now we mount an usb drivE. Please note that it is preferrable to use a fat formatted drive, this uses less resources. This is quite important, considering the notorious usb problems.

See how the drive is called

sudo fdisk -l

in my case:
/dev/sda1

We create the music folder:

mkdir /media/music
chmod -R 777 /media/music
mount /dev/sda1 /media/music

Then we add this line to /etc/fstab

sudo nano /etc/fstab

/dev/sda1 /media/music vfat defaults 0 0

Ctrl+ X then, y
We now add a symlink into the default music directory, this will give us the possibility to store our music library on multiple locations. For example, we can have a part of our library on the nas and another one on a usb drive

cd /var/lib/mpd/music
sudo ln -s /mnt/nas
sudo ln -s /media/music

Installing wi-fi client:

sudo apt-get install wicd-curses

cd /var/lib/mpd/music/

Tweaking

This is a fine tuning of the Pi software echosystem, even if we cannot get rid (as for now) of the usb problems, we can still do something to improve general usb performance. Adding this line to:

sudo nano /etc/modprobe.d/alsa-base.conf

options snd-usb-audio nrpacks=1

This sounds really effective to my hears!

There’s another tweak that should fix the usb problems, you should add a line in the cmdline.txt. This line turns the usb into 1.1 mode. Please note that by doing so, both usb and ethernet performance in terms of transfer speed will be greatly reduced. This doesn’t work for me, as my Usb Dac doesn’t work with this mode. Feel free to try it, please report if it solves the problem with your dac. You can remove this tweak by deleting the added parameter.

sudo nano /boot/cmdline.txt

dwc_otg.speed=1

Next step is to set the Pi’s cpu to work always at its full power. This is due to the fact that mpd for an unknown reason doesn’t trigger the scaling governor to increase computing speed while in use. By enabling the “performance” option, we’ll be sure that mpd has the full power it deserves.
First, we check out which power management profile we have:

cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
powersave

Ok, let’s put the Pi in performance mode:

sudo su
echo -n performance > /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

Check again with previous command to see if it is effective.
Using hw, insted of plug and mmemu

nano /etc/asound.conf

cancel existing text and paste this

pcm.!default {
type hw
card 0
}

ctl.!default {
type hw
card 0
}

LAN TUNING

sudo nano /etc/sysctl.conf

add line

fs.inotify.max_user_watches = 524288

If you should have some problems, remove it. In my configuration I don’t have any problems, but sometimes they could occour depending on traffic and tcp tranfer size.

Adjust limit values of the audio group

First we add mpd to the audio group

sudo nano /etc/security/limits.conf

@audio - rtprio 99
@audio - memlock unlimited
@audio - nice -19

Then we set mpd to have the highest priority (niceness). We do so by adding a script that starts afer mpd that renices it to -20

sudo su
cd /etc/init.d
nano myruns

We put this in the script:

#! /bin/sh
# /etc/init.d/myruns
#
### BEGIN INIT INFO
# Provides: myruns
# Required-Start: $all
# Required-Stop: $mpd
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: Renicing mpd
# Description: Being nice with music
### END INIT INFO
# Some things that run always
touch /var/lock/myruns

MAXTRIES=15
TRIES=0

# Carry out specific functions when asked to by the system
case "$1" in
start)
#
# mount music
#
renice -n -20 -p `pgrep mpd`
;;
stop)
echo "Exiting myruns"
;;
*)
echo "Usage: /etc/init.d/myruns {start|stop}"
exit 1
;;
esac

exit 0
Ctrl+ x then y

We then set this as script and we add it to the init.d boot sequence:

chmod 755 myruns
update-rc.d myruns defaults

NAS tuning

sudo nano /etc/fstab

adding line
uid=mpd,file_mode=0644,dir_mode=0755,iocharset=utf8,rsize=130048,wsize=4096

Now we selectively deactivate some process, so they don’t start up nad we’ll have less active processes.

sudo apt-get install rccconf
sudo rccconf

The services I disabled:

cron – scheduler
lightdm – graphic login manager
motd – message of the day for ssh
plymouth- graphic bootlogo
x11-common graphic interface

This broke somehow my ssh server, avoiding me to connect via ssh, so be aware of it. If this will happen you should have access to your pi via a monitor and a keyboard and reinstall sshd via those commands:

sudo apt-get remove openssh-client openssh-server
sudo apt-get install openssh-client openssh-server

Now, we proceed to remove everything we used to compile and several things more. In case we don’t think we’re going to recompile something again.

sudo apt-get remove autoconf automake autotools-dev binutils build-essential dpkg-dev g++ g++-4.6 gcc gcc-4.6 libglib2.0-dev libid3tag0-dev libsamplerate0-dev libstdc++6-4.6-dev make pkg-config git-core x11-common dbus-x11 libice6 libx11-6 libx11-data libx11-xcb1 libxext6 libxi6 libxmuu1 libxtst6 xauth xkb-data fonts-freefont-ttf

cd /home/pi
sudo rm -rf mpd

That’s all folks, shake and serve with ice!

L'articolo RaspyFi Rc2 – How it’s made and list of all the optimizations sembra essere il primo su RaspyFi.