I just looked through a list of thumbnails on YouTube and I think I know now what kind of thumbnails I prefer at least:

There should preferably be two people on the thumbnail, facing each other

If there is only one person, there must be text, and the text must not be continuous

 

Start a new document in VS code, and before saving, type:

Worklist
Describe how the certificate registration works

Hit return, and the line now says (my bold):

Worklist
Describe how the certificate registration WorkList

At least on my machine. That is insane! VS Code has no idea of what I am trying to code or write or even in what language yet.

You can get rid of this behavior in settings by disabling:

"Editor: Accept suggestions on Enter"

And I won't buy them because I want the USB and power connectors to be internal to the box, since I will plug in a sound card there and a power bank, and I want those to be integral to the box.

However if that weren't the, uhm case, then these would be on my shopping list:

• One with a built-in screen: Aluminium Case KIT for Raspberry Pi 3 with 2.2" Screen / programmable buttons - Audiophonics
• Aluminium Ultra Thin Case KIT for Raspberry Pi 3 / Pi 2 - Audiophonics
• Aluminium Case and Accessories for X400 Module and Raspberry Pi - Audiophonics

Going deeper into the world of Raspberry Pi and sound I have discovered some new options. Modep (Meet MODEP - MOD DUO Emulator for Raspberry Pi)  is a ready-made operating system image with almost 200 plugins installed. I haven't tested it yet, but I am very curious as to how well they solve the optimization issues. I'm downloading it right now. There are even two de-essers among the plugins! I suupect though that many of the plugins are made for guitar effects and are hence in mono.

Modep is hosted by the Lithuanian Blokas guys who make the Pisound high-quality sound sound card for Pi. Buy Pisound - Sound Card & MIDI Interface for Raspberry Pi. At around €100 I will refrain to buy it at this point in time, since I think it is the processing limits of the Pi itself, that sets the limits for me. Still cool though!

Review: Blokas PiSound, Audio & MIDI Interface For Raspberry Pi : Ask.Audio

Modep seems to be created by the guys behind the super pedals  Mod Duo and Mod Duo X. Their stuff looks close to what I would like to create except they do guitar effects.

Finally, since I have problems with the processing power of the Pi, maybe it's time to look at PureData, maybe the bare bones approach would yield more powerful results, suitable for a headless configuration?

Update 2019-03-10: Couldn't boot with Modep from a USB stick with a Raspberry Pi 3 B+. It complained about things being on different partitions or something. Either the Modep image cannot handle the 3B+ hardware or it cannot handle being on a USB, I guess.

First of all, kudos to the porters and maintainers for making all of these run on the Pi!

However it seems to me that it is the Rakarrack that actually runs well, given the constrained resources of the Pi. And this is not so strange given that I think Rakarrack was made with the ARM-powered Pi in mind!

When running the two others, Jackd seems to give up eventually. It starts outputting lots of clicks, like rain. I think that happens when many samples are dropped so that the result has huge discrepancies between adjacent samples in the output. Then it goes downhill from there and locks up. Basically these two seem to strain the resources of the PI. Maybe their plugins are inherently more computationally complex, or they have not been properly optimized for the ARM architecture.

Thinking about it, I actually only tested the Calf plugins for Jack Rack and Calf Rack. It may be that they are extra difficult on the Pi: Plugin performance on RaspberryPi 3 | rncbc.org

I got here:

https://lucidbeaming.com/blog/setting-up-a-raspberry-pi-3-to-run-zynaddsubfx-in-a-headless-configuration/

In a quick test this morning it seemed to make a difference although some of the adjustments had already been made. Jackd had already prioritized up things. The things I did that were new were the following:

1. Disable the internal audio card by commenting out the "dtparam=audio=on" :

sudo nano -w /boot/config.txt

...

# Enable audio (loads snd_bcm2835)
# dtparam=audio=on

2. DBus security policy (disclaimer: I have no idea what this one does in this context):

sudo nano -w /etc/dbus-1/system.conf

...
<!-- Only systemd, which runs as root, may report activation failures. -->
<policy user="root">
<allow send_destination="org.freedesktop.DBus"
    send_interface="org.freedesktop.systemd1.Activator"/>
</policy>
<policy user="pi">
    <allow own="org.freedesktop.ReserveDevice1.Audio0"/>
</policy>

3. Default configuration to use the USB card:

sudo nano -w /etc/asound.conf

pcm.!default {
 type hw card 0
 }
ctl.!default {
 type hw card 0
 }

4. Force the pi to always be alert, by telling it so on startup:

sudo nano -w /etc/rc.local
...
echo "performance" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo "performance" > /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor
echo "performance" > /sys/devices/system/cpu/cpu2/cpufreq/scaling_governor
echo "performance" > /sys/devices/system/cpu/cpu3/cpufreq/scaling_governor
...

It seems clear now that I have succeeded in building a headphones protector with a Raspberry Pi 3B+, Jackd and Rakarrack.

However some very practical problems remain, and they would actually remain for whatever solution I would have chosen, namely: How do I know I'm feeding the compressor at the right level? If the input signal is too low, the compressor/limiter may not kick in.

So I need an indicator, a VU meter that it is indeed being fed at a good level. I could go the route of having a VU meter directly monitoring the input before it reaches the Pi, but that would be a lot of tinkering.

Since Rakarrack already has built in meters for input and output, it's probably better to outfit the Pi with a small screen, and then create a viewport with xrandr that ensures that those meters of Rakarrack are displayed. And it should be a touch screen so the sliders adjacent to the VU meters can be used.

The second problem is the output level. I would really like to have an analogue potentiometer to be able to adjust the volume there, outside of the Pi. However making a voltage divider with the headset as a part in it, will introduce weird non-linear responses, since headphones vary in impedance depending on frequency. I better go and check to see how much headphone impedance does vary with frequency…

So I am trying out a Raspberry Pi 3B+ as a headphones protector, running a cheap USB sound card in duplex mode and sound processing being done in Rakarrack. The sound system hanged a lot with "xrun" error messages, even with very conservative sizes of buffer (lots) and sampling frequency (low).

By selecting "no memory lock" those hangs disappeared and were replaced with clicking sounds when the runs happened.

I then ticked "soft mode" and the clicks disappeared. I can now run with low latency, currently 34ms. Since this is for headphone minitoring I don't mind if samples get dropped; it's not for recording.

Maybe I should try to put memory lock back… Anyway, great performance progress!

Update 2019-03-07 I put memory lock back, seems to work fine, so it was the soft mode that made the difference.

I am trying to build a headphones audio processor with Linux, and today I got a proof of concept running. It's not running on a Raspberry pi yet, but I tried it on a laptop. An equalizer and a compressor was applied to the signal, and the processed version came out with a barely noticeable delay.

Hardware used

• An Acer laptop
• An old Philips USB sound card that came with a pair of headphones many years ago. It has a mic input and a headphone output. A cheap audio interface like Xenyx 302 USB is a worse choice here, since it plays the input sound over the USB mix.

Software used

• Ubuntu Linux 18.04
• Ubuntu Studio components including Rakarrack
• Low latency kernel

Setup and problems

The laptop refused to switch to the USB sound card. The solution was to kill jackd, and start it from the command line. I have no idea how jackd is automatically started by the way. It's not reachable by service or systemctl. Start it up indicating the sound card to be used. I think the problem is that qJackCtl never managed to modify or restart jackd, it just pretended.

Rakarrack, a guitar effects host, is more stable than Jack Rack so I used that.

In qJackCtl, patches would already be correctly set up by Rakarrack.

Modify the rack in Rakarrack to contain an equalizer and a compressor.

The sound of the mic input on the card should now be routed through Rakarrack to the headphones output. At least it did for me.

Next step will be to get this running on a raspberry pi! That means an Arm version of all this.

I've only watched two so far but his guests are really knowledgeable, for example in this video on lighting:

https://www.youtube.com/watch?v=iiUTTk67kXE&t=683s