@nico readsf~ will do it, but as you say you need to know the total samples...... so here an array has to be written by soundfiler to get that value...... shuffle.pd
There might be another way to get the value, and of course once you have the array you could read from that (in RAM) rather than using [readsf~] as that would be much kinder to your hard drive.
David.

@VitaminK You can use [delay] which will hold your bang, and send it out later.
Spigot is fine.
Something like this should do it....... 10 seconds before the random messages are allowed through the spigot..........
Change [delay 10000] to [delay 5000] for 5 seconds etc.
For 2 minutes....... [delay 120000]

David.

@reflect_ In words......? Hmm.
Say you have a sine wave, and it starts at 0 and rises to 1 falls back down through 0 and keeps going to -1, where it reverses direction and rises back up to 0....... one complete cycle.
So................ 0, 1, 0, -1, 0
x -1................ 0, -1, 0, 1, 0..........inverted...... the whole waveform upside down.... all +ve become -ve et vice versa.
x 0.5.............. 0, 0.5, 0, -0.5, 0......... the wave is half the height, so half the volume.
It is the multiply by "minus" that inverts, and the "one" keeps all at the same volume.
David.

((Well...... nearly....... volume is another thing, power etc., area under the curve...... life, the universe and everything.)) it is obviously late and tine for bed.......

@amazingrolo Just guessing...... although I am 99.9% sure [date] gets its data from the system date, and not from the internet.
The Rpi updates from the internet, which I know because I have never set the date on mine.
To test you could disconnect Wi-Fi.......... set a different date in the Pi...... and see what [date] then pumps out.
A little more info from Google....... https://raspberrypi.stackexchange.com/questions/8231/how-to-force-ntpd-to-update-date-time-after-boot
David.

@reflect_ It is good, but you need to start both tracks at the same time I imagine.
Here is proof....... cancel.zip
Cick [start( to play both (the same track in both players) at the same time, and disconnect either of the receives from the [dac~] to know that it is working....... because there will be no sound..... total cancellation!
David.

@EsGeh I have seen it recommended by Miller to get audio working correctly on a RPI...... just applied to /bin/pd
You can always change it back if it doesn't help.
4755 user can read write and execute, group and others cannot write.
I am no Linux expert, but you have maybe provided enough info for @EEight to spot something.
David.

@EsGeh You should not be having these problems. At all. Except "resizing a table".
Even that should not cause a problem if it is hidden in a sub-patch and you are not reading from it as you resize.
I can run a 64ch in 64ch out mixer controlled by osc messaging from 64 tablets in Pd, at 3ms latency without a glitch (Extended on Windows7)

Are you running Pd at the same samplerate as your soundcard?
Are you trying for too small a buffer to improve latency?
Have you given Pd root priority (chmod 4755)?

Could you post some more detail..... os, soundcard, Pd version?
Chapter 2.5 ........ https://puredata.info/docs/manuals/pd/x2.htm/?searchterm=i/o error
explains what Pd gets up to, and why it is best to hide unused gui's, and there is more help on that site.

You can run more than one instance of Pd and communicate between them through ports, and that will sprout 2 instances of wish, which spreads the gui load as well. Whether your OS will run them all in the same processor I don't know. Recent OS's should automatically spread them about.

I have had problems trying to control a gui through more than 2 levels of gop.
If you wish to post a problem patch then we can see if it works well on our systems, which might narrow it down.
David.

@vvillain If you have connected a [print] object directly to the outlet of [udpreceive] that is not what would print.
You must be unpacking the OSC messages....... with [unpackOSC] maybe?
Have you put a [route /something] afterwards?
If you have not tried to route the OSC messages after [unpackOSC] then Synapse is simply not sending the messages you are looking for, or at least not to port 12345.
David.

@catkisser666 Yes, it is possible, a bit harder with stretch than it was with Jessie..
You will need to open your patch with a something.desktop file in the pi/.config/autostart folder.
Pd will need to be set as default program for the patch.
That will start Pd and open the patch after the X window is started and the whole Pi is booted up...... much the same as you are doing manually when you run it "not headless".
Permissions will need to be set for the .desktop file.
Here is an example of a .desktop file that starts a server on my Pi.....

[Desktop Entry]
Encoding=UTF-8
Type=Application
Name=X11VNC
Comment=
Exec=x11vnc -forever -loop -passwd present -display :0 -ultrafilexfer
StartupNotify=false
Terminal=false
Hidden=false

and here is one that runs a script.....

[Desktop Entry]
Type=Application
Name=RebootMessage
Exec=/home/pi/bin/newstart.sh
Icon=system-run
StartupNotify=true
Terminal=false
Hidden=false

David.

@Gammerjoaq Sorry about the last post...... I should have read the thread.
This is a different way of doing it..... pitchshift-mod.pd
It's a hack of one of the Pd "doc" examples, and so there could be some redundant stuff for your purposes..... but not much.
The value to subtract from the incoming midi note I have set to 58 for testing, and that could easily be the incorrect value for your sample........ assuming you will always know the pitch of the sample........
David.