10 Sept 2016

Notes on using SamplerBox.org on a Rasberry Pi Model B.

After being put onto this by a friend (Hi alex), I spent this arvo checking out Samplerbox. It's a RasberryPi program and system image. It's basically an appliance thing. (I'm not really sure how one describes these things)

the key steps to using it are:

• download the image (Here is the latest image from the forum. the link on the website download link was not up to date at time of writing)
• write the image to an SD Card.
• Plug it into an RPi
• Plug in a USB Midi keyboard
• Plug in some speakers
• Plug in power and away you go

you can do extra stuff, like add hardware for a MIDI In port, and some LED indicators to tell you which patch number you're on, and Patch Up/Down buttons as well. but you don't have to, which makes it super quick to get up and running.

The recommended way of getting started is using the image and writing it to an SD card, but there is a sourcecode repository for the Samplebox python application as well. So i did that. And it does what it says on the tin. Which is great!
I am doing my testing on the original RPi B, so performance wise it's not the greatest.

I'm using a mac, so to write the image to the sd card, you need to use diskutil to unmount the SD card so you can then use dd to write to the card.
Assuming your SD card is disk2, (you can check this by going diskutil list ) you would unmount the card by going
diskutil unmountDisk /dev/disk2
and then to write the disk image do :
dd if=samplerbox_20160831.img of=/dev/disk2 BS=1M
You'll either need to be root, or using sudo to make this work.

An update. There is a faster way to write the SD card images documented on This page
Apparently using the raw /dev/rdisk is faster.

My first testing was done with the internal sound card, not a (recommended) USB one since i'd have to find a USB Hub.

• #1 the samplerbox build doesn't like GUID Partitioning Scheme. It detects a disk, and tries to mount it, but the mount point is empty. This means, on a Mac you can't use the GUI application "Disk Utility" to make your FAT32 disk, you need to do it via the command line. this is the command i used to create my 32GB USB disk to hold my samples.
  diskutil partitionDisk /dev/disk2 1 MBRFormat "MS-DOS FAT32" "HI" 31G
• #2 when you change your patch bank, the system needs time to load the entire sample patch from the media.
  4 seconds for the Juno sound patch (about 50MB)
  21 seconds for the Grand piano patch (about 1.1GB)
• #3 there is no velocity scaling. but there is velocity layer switching. so what that means is there is no adjustment of the volume level other than switching between different samples based ont he velocity played. so if you have 3 layers of velocity samples, you have 3 volume levels.
• #4 The onboard sound is ok for synth sounds, but horrible for piano sounds. but we knew that already.
• #5 It's really easy to get going.
• #6 Latency felt ok. on the Axolti boards, latency is freaky fast/low, but this felt decent.

Things to do next are to Try it with a USB Audio Interface and there are also some patches for changing velocty responsiveness

So some further testing this afternoon involved testing it with a USB Hub and USB Audio interface

• Latency w. the USB interface (A Behringer UCA-222)seemed to be a little bit higher than with the inbuilt audio
  
• Audio Quality on the other hand is much better.
  
• CPU usage is very reasonable when playing. with 8 notes being played, cpu usage was ~30%. with nothing being played, cpu was ~18%
• Holding down 16 notes, CPU usage was ~43.5%
• Holding down 22 notes was ~52%, and the occasional click was occuring
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