• FAQ

  • Input/Output amount, Compatibility

I've read the FAQ and found technical information about inputs and all that, however since it's pretty confusing and scattered around, I'd like to make sure I'm not getting it wrong:

How many jack inputs can the bela have, and how many jack outputs can it have (simultaneously?).
Does the amount of inputs affect the sample rate? Do the outputs matter in this also for some reason? If yes, please specify to what extent.
Edit: specifically, for a 44.1k sample rate since it's the most common. Also, how many cables would I need (jack to whatever the bela uses)?
Edit: Do I need some outside power for the microphones / speakers. I know the Bela has (2?) built-in amps for the speakers, yet being a newbie in audio hardware I'd like to know the exact optimal setup. (and what the heck is the phantom power term everyone is throwing around?)

Does it still have hdmi out cable support? If not, how is debugging / development handled (for both OS installation and programming the controller)?
Ethernet cable support?

What is the usual latency of the bela if the input is directly buffered into the output without any calculations?

How is the bela powered when not connected to the computer?
What cable is necessary to connect it to a computer?

Am I able to include "standard" c++ libraries (like <chrono>, <functional>, <atomic>, <thread>...)?

Addtionally, I'm looking to use the bela due to its multiple inputs/outputs capability and its very low latency, it is for a school engineering project, so if you think there is anything I should know regarding this topic, please add it.
Thank you!

Both the regular Bela starter kit and the Bela Mini have stereo audio in and out, i.e 2 input and output channels. We bundle audio adapter cables with the kits which allow you to connect using stereo 3.5mm audio jacks.

The sample rate for these inputs and outputs is fixed at 44.1KHz for both.

With the audio expander capelet you can convert the regular Bela starter kit's analog i/o to audio, giving you an additional 8 audio channels at 22.05KHz, or 4 channels at 44.1KHz, or 2 channels at 88.2KHz.

With the CTAG capes you get a lot more audio channels, 4 in 8 out with the FACE or 8 in 16 out with the BEAST.

Whether you need external power depends on what kind of speaker and microphone you are using. The regular Bela cape has speaker amplifiers on the board which work when you supply 5V through the barrel jack of the BeagleBone. Most speakers will require some form of external power, such as a battery.

Phantom power is only required for certain kinds of microphones, so look at the data sheet for the one you are using.

There is no support for HDMI, instead you connect your Bela to your laptop or desktop computer over USB and use our browser-based tools for debugging and development. Ethernet is also supported on the regular Bela kit.

You can power Bela with a battery connected to the USB port or barrel jack when it is not connected to a computer. Cables for connecting to the computer are included in the kits, they are regular USB cables (mini for the regular Bela and micro for the Bela Mini).

You can use whatever c / c++ libraries you like.

    LiamDonovan Alright, thanks a lot! Just an extra question:

    Do the microphones / speakers add to latency depending on which I choose?

    Edit: oh and also, how is data formatted in the input? Is it all saved into a "input" buffer for each channel? What value is used for the buffer (is it an array of ints, floats... and if so, from how much to how much (min and max value possible)?)
    Edit: also, are the FACE and BEAST capes meant to be expansions to the bela or are they added on top of the beaglebone black directly? In either case, is the sampling rate for them the same? And is it possible to have more inputs than outputs on them instead?

        ZeroZ30o and also, how is data formatted in the input? Is it all saved into a "input" buffer for each channel? What value is used for the buffer (is it an array of ints, floats... and if so, from how much to how much (min and max value possible)?)

        It's saved as float in interleaved buffers. Range is -1:1 for audio I/O and 0:1 for analog I/O

          ZeroZ30o dit: also, are the FACE and BEAST capes meant to be expansions to the bela or are they added on top of the beaglebone black directly? In either case, is the sampling rate for them the same? And is it possible to have more inputs than outputs on them instead?

          FACE and BEAST can work with the Bela cape but do not require it.

          Number of I/O is fixed: 4in 8 out for the FACE, 8 in 16 out for the BEAST

            LiamDonovan >Phantom power is only required by certain microphones.

            I found a mic I'm interested in that requires phantom power -is the bela able to supply this or do I need some special kind of wiring for power on top?

            Edit: the data sheet is not specified but it's a condenser mic with no other power sources, so I assume it must use phantom power?

                ZeroZ30o Edit: the data sheet is not specified but it's a condenser mic with no other power sources, so I assume it must use phantom power?

                maybe it is an electret condenser and it only requires plug-in power (2.5V) ? The latter is provided by the Bela cape, while the Bela Mini provides 3.3V (which is normally just fine), however both will require you to install an external resistor.

                    giuliomoro How much voltage can the bela supply for each microphone?
                    And is there a recommend output impedance range for microphones plugged in?
                    What happens if the output impedance of the microphone is too high/low for it?

                        ZeroZ30o How much voltage can the bela supply for each microphone?

                        2.5V or 3.3V. So that is really only good for electret capsules that require "plug-in" power

                        ZeroZ30o And is there a recommend output impedance range for microphones plugged in?

                        the microphones will have a recommended minimum load impedance. The audio inputs have 20k ohm input impedance.

                        ZeroZ30o What happens if the output impedance of the microphone is too high/low for it?

                        It's the other way round: "what happens if the input impedance of the device is too high/low for the microphone?" It depends on the mic and it normally happens only if the input impedance of the device is too low. The effects could be a combination distortion, change in the frequency response, low volume.

                                giuliomoro So, I've found a microphone with 2.2k Ohm impedance. So if I understood right this is fine, since the bela's inputs have 20k impedance which is way higher than 2.2k? Or is it the other way around?

                                  that should be fine. Does it mention the minimum load impedance?

                                    giuliomoro Not that I can find, no -in fact it only says "Impedance: 2.2k" and "Power: 3v" aside from the sensitivity and the frequency response range

                                      7 days later

                                      giuliomoro So if I plug in microphone's jack outputs to the bela I must also add an external resistor (if the microphone requires phantom power)? If so, how?

                                      For speakers, I'm assuming the bela can't supply their power, is this correct?
                                      Is there a recommended resistance for speakers (should it be as low/high as possible, or close to a certain value?)?

                                      Thanks again!

                                          ZeroZ30o So if I plug in microphone's jack outputs to the bela I must also add an external resistor (if the microphone requires phantom power)? If so, how?

                                          Yes, to provide plug-in power (not phantom). How you fit it depends on your configuration. It could involve a bit of (careful!) soldering on the Bela cape.

                                          ZeroZ30o For speakers, I'm assuming the bela can't supply their power, is this correct? Is there a recommended resistance for speakers (should it be as low/high as possible, or close to a certain value?)?

                                          You can drive passive 8ohm(no lower than 8ohm) speakers directly from the on-board amplifiers, which can provide 1.1W(max 1.1W) (though these will only work if Bela is powered through the barrel jack). If you need different/more powerful speakers, they will have to be externally powered.

                                                giuliomoro So regarding the microphone, which specifies that it is "plug and play, no need for an external power source", do I need to worry about anything extra?
                                                The impedance and voltage are also mentioned: 2.2Ohm and 3V. Nothing else.

                                                Knowing all that, if I only connect these microphones to the bela, will it be able to handle them correctly? If so, how many?

                                                After that I should be set for hardware specs since I'm already set for speakers. Thanks again by the way.

                                                    ZeroZ30o do I need to worry about anything extra?

                                                    by the sound of it, they should be fine, but I cannot be sure if I don't see the datasheet.

                                                    ZeroZ30o 2.2Ohm

                                                    That is probably 2.2k ohm?

                                                    That is weird, what is that meant to be?

                                                    Can you send a link to the microphone page?

                                                    ZeroZ30o If so, how many?

                                                    There are two audio inputs, so two microphones, I suppose.

                                                    giuliomoro You can drive passive 8ohm(no lower than 8ohm) speakers directly from the on-board amplifiers, which can provide 1.1W(max 1.1W) (though these will only work if Bela is powered through the barrel jack).

                                                    Forgot to mention: this powered output is only available on Bela (not Bela Mini)

                                                                giuliomoro Here is the "datasheet", that is all the info available on amazon's description of the microphone:
                                                                https://i.imgur.com/Bqb0Zdv.png (it's in French though)

                                                                The microphone itself is called "XIAOKOA PC condenser microphone"

                                                                Thanks for the rest though

                                                                  Yes it will be fine. Use a 3k3 resistor from 3.3V (pin P9_03) to the input your mic is connected to.