Sound engineers used to connect all of their gear with patch-cord cables. In the twenty-first century we have graphical user interfaces.
Our HardwareThe screen captures are from this machine, running AVLinux. In Basic Windows Audio Tourwe looked at the same mini-PC. You can compare screen captures.
The PC has the front microphone and headphone jacks connected to a sound input/output circuit from Realtek. A DisplayPort classic port on the back will show as HDMI audio on our menus.
Operating SystemRunning AVLinux orUbuntu-Studioon your computer is the best way to follow along with this project. Built around a real-time kernel with tools for sound management they also come with suites of specialized audio and video editing softwares.
Uname -a CommandOpen a terminal, enter the command $ uname -a which shows information about the Linux running on your computer. PREEMPTmeans the computer has a real time kernel. It will be more responsive to external interrupts.
The date shown is when was this kernel compiled and released. Real-time kernels are used in industrial control systems because of their quick response.
Still a normal computer operating system. You can write word and excel documents with Office softwares and surf the web.
Graphical User Interface GUIJack andPipeWireare sound management systems that work with ALSA and PulseAudio. This is very technical stuff. A picture interface makes it much clearer.
If your Linux computer does not already have one of these programs installed then just read along. Ubuntu may offer to add but properly implementing a multimedia studio is complicated.
Type qjackctlOpen a terminal and type qjackctl. Linux with Jack installed will open a little window that looks like a media player. This one did not start the Jack Server automatically and we need to fix this.
Click Messages and read the messages. It says the server tried to run but failed. You can close Messages.
Change SetupClick the Setup button and a new panel shows our default sound interface. It does not work with Jack so we will change to our analog audio circuit from Realtek.
Click the interface selection and look for your sound card.
All these changes need you to apply them. The Jack server may restart automatically or you need to click the green play button on the jack control panel.
You should see a map of sound connections through your machine. Try the Zoom Fit button. Re-arrange the boxes until they make sense. MIDI is a digital musical instrument signal we are not using.
Play a song or movie with sound. Open the Pulse volume control either with the speaker icon or with the terminal command pavucontrol. New sources, sinks and connections may appear as Jack automatically detects them.
Right-click directly on each connection arrow. Each sound source or sound sink can be connected or disconnected from this panel.
We are going to change parameters for our audio channel in order to reduce latency. To work with sound a computer samples the analog world and turns the sample into numbers. Sound is delayed and we call this latency.
Listen to your speakers and tap your microphone. The sound input buffer is where you hold sound samples for processing. Default values for the buffer are larger than necessary.
Buffering 3 sample periods of 1024 frames introduces a delay of 70 milliseconds. This is one fourteenth of a second and we can hear this.
Change your buffer to 256 frames for 2 periods. Click Apply. Our latency will be under 12ms. Can you still hear the delay?
What does Advanced do?The Advanced tab lets you create audio where separate circuit devices handle in and out. Neat, eh?
If your Linux does not run Jack then try Pipewire. Open a terminal and type qpwgraph. Does a graphical window open? Like Jack it shows a map of our sound connections.
PipeWire DemoThis shows a simple application of playing VLC and operating the volume control. We are not using MIDI signals but you should still see the blocks in the window.
Look in your Sound and Video menu for the pipewire PW utilities. Open each one here or use the CLI commands.
You will see status messages and settings for the graphical utility and sound in the computer. Read through and look up terminology.
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