Hi, I’m a newby on Zynthian world.
I’ve Zynthian v.4 and i would like add 2 analog input in order to add fx on 2 synthesizer
1- Do you think it’s easy to add 2 analog input ?
2- Do you think I can add 2 6,5 jack analog input in zynthian box ?
No, you cant add channels to the zynthian sound card. You only can replace it with a usb audio interface which is supported by Linux.
Hi @MrFuZ, welcome to our community. The V4 Zynthian has two audio inputs and two audio outputs. If you need more you will have to add a USB multi-port audio interface like the Behringer UCM1820. You can’t combine them, you can only use one audio interface at a time, e.g. one USB device or the built-in sound card.
Mmh all right, thanks for you’re answer
I’ll looking for usb sound card
I moved this to a different topic as it wasn’t relevant to the topic in which it was initially added. (Please try to stay on topic or create a new topic if required 
.)
@MrFuZ Just checking, you are wanting more than 2 inputs in total, i.e. the existing 2 inputs are not sufficient for you? What do you intend to do with more than 2 inputs?
I’would like add fx on different input. For exemple jack input 1 and 2 add reverb on my drum (akai mpc) in stereo.
Input 3 add flanger on my synthesizer
Input 4 add fuzz on tb303
Okay - so you want multiple inputs to allow many different audio sources to be individually processed then mixed to a single stereo output. (If you had multiple outputs you could mix externally but that is not the subject of this topic.)
Computer audio will generally require a single ADC for all input channels. This is because the sampling of the audio needs to be synchronous to ensure the internal engine can process the same amount of data, i.e. not be missing some or have too much. This is most simply implemented by only accessing one soundcard so ALSA presents one of the available soundcards to jack which can then transport the audio synchronously. Passing the audio back to the same soundcard for output works because its outputs are clocked at the same rate as its inputs, hence alsa and jack all get clocked at the soundcard’s clock rate. Alsa can set parameters on many soundcards to choose from the card’s available samplerates, hence a soundcard may allow its clock to be set for 44100, 48000, 96000, etc. There are ways to join multiple soundcard inputs / outputs but this involves the sound system clocking at one rate then samplerate converting (SRC) (using CPU / DSP) anything that is not locked to this clock. The computer may lock its audio to one soundcard then SRC any other soundcard audio. (This is how we add headphone output in Zynthian.) Such a process takes a significant amount of processing which reduces available CPU (and other resources) from the main task of making sweet music - so this is undesirable. Professional audio soundcards can also be locked together - they may have a word clock (or similar) input and output which can be linked so that one card slaves to the other and runs its ADC/DAC at the other card’s clock rate. This may also be done by clocking from a digital input, e.g. AES3/SPDIF/ADAT.
So although you didn’t ask for it, that was a bit of theory which explains the challenges of using more than one soundcard to increase the number of inputs / outputs. It is far cheaper to buy a multiport soundcard than to get ones that link together and it is inefficient (unwise) to use SRC to do this task.
There is a sound subsystem called Pipewire which allows different soundcards to be used together but it does so using the SRC method and hence, unless they have discovered a magic potion, will be hard on the CPU in a Raspberry Pi. We are not (yet) using Pipewire but keep a watchful eye on its development and progress.
So, to do what you want you should get a multiport audio input card that is supported by ALSA. If the card works without a special driver on platforms such as Windows and MacOS then it should work on Linux with ALSA. There is a standard for USB audio called USB Audio Class Compliant. This is a plug and play thing that allows USB audio devices to work on Windows, MacOS, Linux, etc. without extra drivers. The Behringer range of soundcards work as do many others. There is some resistance by some of our friends to Behringer for various reasons but they do work and they are relatively cheap. The UMC202HD has 4 inputs and outputs for about £100 whilst the UMC1820 has 8 analogue inputs and outputs and it cost under £200. These both work out-of-the-box with Linux on Raspberry Pi and have webconf configurations in Zynthian. They are good value, providing quite good quality microphone preamps with XLR/Jack combi-sockets allowing instrument input or mic input.
If you search this forum you will find many people’s experience of using external and internal soundcards with the Zynthian. I don’t think anyone got a multichannel audio hat working - at least not one that is actually available to buy! I do like the Behringer for its versatility and value which I didn’t think I would hear myself saying after years of berating them for their quality control and tendancy to break within a few years.
I recommend you assure yourself that the device you obtain works properly with Linux before you purchase it. You can end up with a dead donkey if you buy unwisely.
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