Bela Cape, Audio Expander Capelet and Multiplexer Capelet




These are the hardware components of Bela: The platform for ultra-low latency audio and sensor processing. You might also want to read the blog article Bela: analogue vs audio | Bela Blog.


Bela cape



  • Audio: 16-bit stereo audio I/O at 44.1kHz
  • Audio power output: 2x 1W 8ohm speaker amplifiers (available when powered from DC jack)
  • Analogue In: 8x 16-bit analogue inputs at 22.05kHz
  • Analogue Out: 8x 16-bit analogue outputs at 22.05kHz
  • Digital channels: 16x digital GPIO at 44.1kHz or 88.2kHz
  • Analogue I/O is also software configurable to give 4 channels at 44.1kHz or 2 channels at 88.1kHz


The Bela hardware cape consists of a stereo audio codec (TLV320AIC3104), an eight channel 16 bit DAC (AD5668) / ADC (AD7699) for DC-coupled analog IO and a headphone preamplifier.


Bela cape: Hardware explained



Bela Audio Expander Capelet


The Audio Expander Capelet converts the analogue I/Os into extra audio inputs and outputs. With this capelet you can have up to 6 total audio inputs and 6 outputs, all sampled together at 44.1kHz. Alternatively, you can go up to 10 inputs and 10 outputs, with 8 of those sampled at 22.05kHz.


To use the analogue I/Os as extra audio channels, then, we need to do three things. First, we need to provide AC coupling so we can send and receive bipolar (positive and negative) audio signals. Second, we need to add some extra analogue filtering to make up for the lack of onboard digital filtering in the SAR ADC and string DAC. Third, we need to match levels between the analogue and audio converters, which can be done in either hardware of software. The capelet does all of these things.

Bela: analogue vs audio | Bela Blog



Bela Mux Capelet


The Bela Mux Capelet is an add-on multiplexer for your Bela system. This capelet can expand your 8 on-board analog inputs up to a massive 64.


Please note that the analog inputs are each sampled at 22.05kHz, and expanding your inputs will lower your sample rate. When you use the Mux Capelet the Bela software will automatically cycle through all the inputs, giving you 2.75kHz sample rate (22.05kHz / 8) on each of the 64 inputs. Alternatively, you can use 32 channels at 5.5kHz or 16 channels at 11kHz.