soundcheck's sKit toolbox

 (Latest update: Dec-21-2021)

I was thinking of how to get most relevant and applicable learnings from the Audio Streaming Series easily applied to all the systems out there. Simply to make sure that everything ends up as intended and satisfactory for you in a couple of minutes.  

After looking into it, it turned out that many of the measures I've been outlining would make a nice small set of tools. (similar to my Squeezebox Touch Toolbox project from 10 years ago). 

One of the project goals : Even fellow audio-enthusiasts who lack in-depth computer skills should be able to get things done easily.

And this then finally led to 

sKit

(soundcheck's tuning Kit)  

sKit provides a small set of tools to customize and enhance the piCorePlayer base OS for improved audio performance.

sKit currently supports a streaming-client scenario only.
Just squeezelite and no LogitechMediaServer! A combined client-server setup (standalone player) would require a different tuning profile.

All sKit tools are supporting and focussing on my highly recommended HW platform:

A Raspberry Pi 4B.  

(CM4 modules and RPi3 and related CM3 modules might also work - no promises made - I don't have them and won't test and won't provide any support for them).

The sKit toolset expects the 64-bit pCP versions. That's the pCP version you should have installed.

sKit has been tested on pCP Versions > 7.0 up to 8.1 . 

Please upgrade to the latest pCP version and the most up2date software before you start the journey.  

PLEASE: Do not contact me if you run into issues while trying sKit on a different platform!

sKit currently neither supports USB boot scenarios nor netboot scenarios. (a pCP shortcoming)

All sKit tools have to be executed from a pCP linux terminal. Many of you meanwhile know the process of how to access such a terminal via ssh.  If you don't know how to do that, have a look at the official pCP documentation to be found over@pCP  first.  

Once you're logged in to your RPi via ssh, you simply have to enter one of the further down listed commands to get this or that job done. A piece of cake! No hacking!

All sKit sources a stored on github. There's nothing to hide. You'll be on the safe side. You can lookup the source about what's actually done.

Before using the sKit tuning kit: Make sure you have a look at The Audio Streaming Series to have your system, prepared and properly up'n running. Not all recommended settings are covered by the tuning kit (yet). Beside that you'll get the idea what this is all about.

 

To be prepared for sKit after a fresh pCP install, you need to have at least following bullets ticked off:

1. increase the filesystem to at least 500MB (we need ~100MB free space for sKit)
2. run a patch-,  minor- and  full-update
3. enable your audio device
4. disable RPi built-in audio
5. disable Bluetooth, HDMI  and Wifi (going wired is my preference)
6. configure the squeezelite parameters as I suggested for your audio device
7. test your base setup incl. running some audio tracks
8. run a backup of this configuration, you might have to restore it later on, or
   you can easily do some before/after testing.

A squeezelite settings reminder:

Just to mention it once more, the pCP ssh-login default credentials:

user: tc
password: piCore

Sounds OK and manageable so far!?!?

Let's get sKit installed. 

Initial Installation

The next step has only to be done once. Somehow we need to initialize the toolbox by downloading the installer from github. Once that is done sKit is stored on the system and all further tasks are initiated locally on your system. You'll need an up'n running internet connection to make it all happen!

Let's get started.

Log yourself in to your RPi via ssh.

Now copy/paste below command:

wget -O- https://raw.githubusercontent.com/klslz/sKit/master/download 2>/dev/null | sh

This action will download and install the sKit-manager.sh program to a temporary directory.
Once more: This action has to be done only once!

Now you can install sKit. On the command line prompt, you simply enter the respective program name.

sKit-manager.sh

The sKit-manager will appear. After accepting the sKit T&Cs choose the "1" "install sKit". 😉

During the installation you should see this:

Once sKit is properly installed the system will reboot. You again have to ssh-login to continue the process. 

By now you'll have the system already nicely shaped! Quite some sKit measures will already be in place. 

What's left to do then!?!?  

You'd just have 

• to install a custom squeezelite and 
• turn off the LEDs 

After that you'll be good to go. Most other stuff is optional.

Note: The bold headings ending with .sh on this page reflect the program names (commands) for starting the sKit tools from the ssh command line interface.

Just copy/paste these strings into your ssh terminal.

Now, from time to time there'll be sKit tool updates. Use the update function to get the tools updated. 

Only the sKit tools will be updated.  Not the tuning measures!!! Therefore it can very well happen that you need to start with a fresh pCP install and a fresh install of sKit! I'll inform you about it in the respective release notes. For that you need to start the sKit-manager.sh 

If you're NOT happy with sKit or if I issue a sKit upgrade that requires a fresh sKit installation, you can get sKit removed via the sKit-manager.sh.

Removing sKit removes (from sKit 1.4 onwards) the sKit tools, configurations, the custom binary and restores the original pCP packages (extensions)!  There's shouldn't be much of a trace of sKit on your pCP installation once this step is done.

Keep in mind. The removal process works properly from sKit 1.4 onwards! 

If you still run an older sKit version please start over with a fresh pCP install.

sKit-check.sh

It's usually hard and/or annoying to keep track of all the settings, mods and tweaks on the system. 

You never really know if all the tweaks are enabled, disabled or configured correctly. 

And that's why I wrote sKit-check.sh That's actually the tool I use most.

The tool checks your installation against the recommendations made in the Audio Streaming Series.

If you see a green output, everything should be OK. 

A yellow output hints that the setting has a little space for improvement. Basically not the best of all options, still OK though. E.g. if you're on Wifi - to me it'd just be the 2nd best option after wired ethernet. 

If you'd see red, there's some action on you. Try get them all green first. It'll be a good starting point.

Once you achieved that "GREEN" state and music plays fine,  I'd suggest to run another backup of your SD card.

After that you can play around with your own custom settings. 

Below you'll find values and ranges the tool expects. These cover my most recent and preferred configurations.  

Warning: These might differ from some of the infos you find on the blog elsewhere. Be assured. This spot is the reference spot! I'll try to get the rest of the blog in sync as soon as I can.

isolcpus:            OK if CPU 3 is isolated  (Note: 3 only! it used to be 2 and 3!)
c-s output priority: OK if between 45 and 50

c-s affinity main:   OK if affinity is 1,2

c-s affinity output: OK  if "-A" squeezelite option is set

c-s ram-playback:    OK  if greater or equal than  300000 (300MB) 

c-s alsa params :    USB DACs    - OK    if 160:4::1

                     I2S DACs    - OK    if 65536:4:1

The "c-s" printouts appear as soon as you've got a custom "soundcheck" binary installed.

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sKit-custom-squeezelite.sh

The sKit-custom-squeezelite.sh tool you know from The Custom Engine project.
The tool 

• offers, 
• builds and 
• installs

 different 

• customized (e.g. soundcheck's linear volume control, multiprocessor resampler (MP) ) 
• stripped down and 
• optimized (platform, architecture)

variants of squeezelite.

It selects the "soundcheck - minimal" binary by default. For a reason. You should try it. The 

custom binary and related settings are another key measure.

Beside that the tool automatically configures OS related settings, such as

• system CPU isolation 
• task affinity (assigning squeezelite to each of the isolated CPUs)

 

A whole bunch of things happen with this measure. Before you start the tool, make sure you have 100MB of free space - the tool bails out it there's not enough space. On a fresh installation it is sufficient to increase the file-system to 200MB. The 100MB consists mainly of the pCP compile environment that we store on the SD-card. The 100MB gets only temporary loaded into RAM - only during binary build time.

Note: I did run into pCP extensions download issues - driving me nuts - several times. That's the answer I received from the pCP team, pretty much confirming the shaky behavior of their download servers. A workaround is to try the mirror server to see if that works better. 

Finally.

Do not miss  the linear volume control feature (1dB/click) that comes with the my version of squeezelite! Most volume controls show rather random behaviour, all coming with different attenuation curves. My squeezelite version goes up'n down with 1dB/click. 

You have to enter "-X" for linear internal volume control or "-Y <your-mixer-control>" for external linear control in the pCP WEB-UI under squeezelite settings/various options field.
E.g.

would assign the output-thread to CPU3 (-A) and would enable the internal linear volume control.

 

sKit-led-manager.sh

This tool disables and re-enables the two RPi main LEDs (ACT and PWR) and ethernet port LEDs.

It lowers

• RPi activity
• power consumption
• light pollution

Turning the LEDs OFF saves a little power and stops light pollution in the room. It's been introduced in the advanced base setup article. Just do it. ;)

sKit-tweaks

This tool is NOT supposed to be executed manually from a terminal. pCP will autostart the tool at system boot. During the sKit installation all related configurations were done already.

I am still listing it, because it applies some key measures I'd like to explain.   

This tool runs several system optimizations tasks. It's an enhancement over the Kill-The-Daemons tweaks introduced in the Advanced Base setup article. 

What it does. It

• disables the still active idle network interface (ethernet or WLAN)
• assigns proper squeezelite affinity settings. (workaround for pCP flaw (stat Feb-2021) )
• kills several daemons (after 180s) (WEB interface, dhcp, ssh access)
• ...more to come

You'll find the situation as shown below after the sKit installation . This way the tool is active and being started @ boot time.



To deactivate the tool you need to add a # in front of the sleep command, as shown below, and
press SAVE afterwards. Once saved, initiate a Reboot from the pCP Main page.

 

To simply pause the tool-launch at boot, in case you'd like to run some configurations or changes to pCP from your side, you have to insert the #, save it and reboot.

After 180s - while sKit-tweaks is activated - there'll be neither WEB-access nor ssh access. Make sure you do your changes  during that 180s grace period right after boot. 

And do not forget to re-enable the sKit-tweaks and reboot once you're done with your changes!

If you login via ssh during the 180s grace-period, the sKit-tweaks tool will automatically be stopped!
In this case you wouldn't have run the insert/remove "#" action. There wouldn't 't be a lockout anymore! 

The sKit-tweaks part IMO is one of the key tuning measures! Make sure you got it activated!

 

sKit-src-manager.sh 

The tool provides you easy access to highest quality sample-rate conversion. Keep in mind. What matters if you do digital signal processing (DSP) are the settings of the filters that are being used. squeezelite with libsoxr gives you the framework. We need to get it going.

Now. You're the driver. It's your job to get the horsepowers on the street.
To give you a headstart the sKit-src-manager.sh tool offers a selection of a few sample-rate conversion (SRC) presets that I consider worth trying.  

As outlined in the Audio Streaming Series - The converter and in the  Resampling - If you can't avoid it article from 2011, there are IMO certain good reasons to try SRC. The key reason is that your SRCed data might beat the internal DAC filters and DSP.  This could outweigh the SRC related losses - no DSP is lossless. 

As you can see above. For now I'm offering 4 presets. You should try them all to get the picture. Give each of them a little time to sink in.
My experience shows, there are DACs that show real nice performance jumps, others do not show any change and yes, there are DACs where things get worse. No promises made!

Working with DSPs and digital filters is not an exact science. Every DSP solution remains a compromise.

One more thing needs to be mentioned for now. Inside the pCP Squeezelite Settings menu, you'll find a field Max sample rate. By default, with the Max sample rate field being empty, above presets synchronously resample to the highest possible sample-rate that your DAC supports. squeezelite recognizes the maximum samplerate of your DAC. However. There are cases (my DAC) where the maximum sample rate the DAC is offering doesn't work. That's when u use the Max sample rate field.
Just go one level below you DACs max sample rate. And try that. Below the setting for my iFi DAC.

 

Typical values to try would be: 768000, 384000, 192000, 96000
The uneven values (x*44100) are automatically selected by the synchronous resampling mode!

That'll be it for the time being. I'd really like to hear some feedback on above presets.

Optional Tools

sKit-restore.sh

pCP just introduced a nice backup function. You can run a backup of the booted pCP SD-card image.

And you can store it on an external disk or on the internal ramdisk for further processing with scp.

If you followed my advise of increasing the filesystem to 200MB your image will be about 270MB in size and compressed about 200MB.

For the restore to work you'd have to remote-copy-via-ssh  (scp) your backup image to /tmp or you'd have to attach you backup media and mount it by choosing your image location/save.

Once that is done you can start sKit-restore.sh from a terminal. For a test a pCP backup could be stored on default /tmp/images, leave it there and restore it with sKit-restore.sh .

sKit-restore.sh immediately halts the system - immediately once the data are written back - trying to avoid any corruption issues.  You'd have to re-power the RPi after the restore is finished.

Running online-restores is tricky. I tried to limit the risks as much as possible. However, I can not guarantee that it works for you or in all cases. I did it several times by now and to me it seems to 

work rather stable. Otherwise I wouldn't have released the tool. As usual you run the whole thing 100% at your own risk. You better run some tests first.

Hint. How I do it: I am installing a base pCP image, do all kind of basic configurations, updates, increasing filesystem, setting up the audio device properly before installing sKit. At that point I run a backup. After that I can install sKit. If something goes wrong I just restore the backup. Not even a 5minute exercise.

Each of the actual backup and restore and scp task execution takes less then a minute in my environment. That's great. No more SD cards to carry around. ✌ 

For me as a power-user sKit-restore.sh is a highly useful feature. And it's unique to pCP. No other system I'm aware of, could run an online-restore. Great to have a fully ram-loaded system at hand.

As usual. Feedback, especially on the restore part,  is highly appreciated.

Other goodies

psp 

Introducing an advanced ps (process state) command and a new alias. The vastly stripped down default pCP "ps" Linux command (busybox) is pretty useless when it comes to looking up your process situation. 

Now. sKit installs a small package (procps-ng) that offers the full featured ps. The sKit manager installs also a very useful alias that runs ps with some useful options.

By typing psp in a terminal, you'll get the full picture, about processes, threads, priorities and affinities. This way you can easily verify if all related settings and tweaks are working.

 

What you can see here is, is that a squeezelite-custom version runs @priority 47. And just the output thread runs  @prio48. You also see that all threads except the output thread (CPU3) are attached to CPU2 or 1. That's basically how it looks if everything is properly sKit-like configured.

You can try this command once you're done with the whole setup and tweaking. 

SUPPORT - Trouble Reports

If you encounter issues or if you have improvement proposals, you can either contact me via this blog
or my github presence. For better tracking I'd prefer a github issue request, with at least below information.

• describe your setup 
• RPi revision and type 
• pCP  revision and version (32 or 64bit)
• pCP setup
• audio interface and power supplies
• describe your issue properly
• what's been done - step by step
• describe corrective measures already taken 
• add logfile (to be found under /mnt/mmcblk0p2/tce/sKit/log )
• or screenshots

The more specific you are, the easier issues can get fixed. 

No proper Info  >>  No Action on my side  >>>>  No Fix.

ideas/prospects

I've got plenty of ideas....

• sKit evolution and maintenance  -  pretty solid efforts 
• sKit-custom-realtime-kernel     -  that'd be a major project - and a major step up
• sKit-advanced-tuning                -  there's still much more to gain
• sKit-basic-settings                     - do the pCP basic configs with a tool.
• sKit-server/standalone - combined  server and client operation

      OR even:

• sKit-Moode - piCorePlayer is not the only system with tuning potential
• sKit-Volumio - that applies here again

...and limited resources!!!

Wrap UP

I hope you all enjoy the sKit Toolbox and the improved audio performance it's supposed to bring to you and your beloved audio systems.

I hope sKit  delivers a noticeable Audiophile VALUE to you. That would make the numerous hours that went into the project not a waste of time. Keep in mind - I do all this work just for you folks. I am not using pCP myself!

From the feedback I receive sKit seems to work quite well for many folks out there. That's nice.

Leave a comment if you like what you hear.

 

Enjoy.  😉