ADC/DAC and Digital Audio Processing

https://embeddedcentric.com/adc-dac-and-digital-audio-processing/

LAB 8

***Helpful Note: The tutorial doesn't specify this, but you will need minicom open when running the program.

Also if a warning appears after you have created the HDL wrapper you should be okay to continue anyway.


Summary:

In this lab, we use the ADAU1761 audio codec chip (coder-decoder) mounted on the Zed board, to output different pitches using the switches. Inside the codec are two ADCs, Right Channel and Left Channel, that we used to sample audio. The NCO generates samples of the sine waves at the designated frequencies and these samples are superpositioned and sent to the DACs through the I2S bus, so that they can be played on the speaker.


ADAU1761 is and audio codec chip located on the Zedboard used for audio processing.
  • Used for acoustic purposes (playing, recording, processing).
  • The sample frequency is generated by the PLL logic which is driven by a master clock supplied by an external source.
  • The ADAU1761 cannot initiate a data transfer.
  • Uses two's compliment fix point format

NCO (Numerically Controlled Oscillator) - Generates samples of the sine wave at selected/desired frequencies.
  • The samples of the sine wave are superpositioned on the received audio samples. 
  • The modified audio samples (recieved + sine samples) are sent to the DAC converters of the Codec for playing on the speaker (connected to green output on board).
  • The NCO is implanted in the hardware as an AXI core to provide accurate timing.

ADC are used to digitize audio signals
  • Nyquist Theorem: Sampling frequency of an audio ADC should be at least twice the highest frequency.

After obtaining digitized samples of an audio signal, processing can take place in a digital system.

To play back the processed audio, a DAC is needed to convert the stream of digital values into an analog signal and the analog signal can be sent to the speaker for playing.

The samples travel through (connections) the I2C standard audio bus.

The frequency of the sine wave to be superpositioned on the input audio is set by the switches.
  • The switches/LEDs correspond to their binary value
I2S Bus (Inter-IC Sound) is the standard for transferring audio data within digital systems.
  • Signals: The serial audio data in/out lines
    • two clocks and data lines
    • LRC (Left-Right Clock): Identifies the audio system sample rate and frames the two channels of audio data that exists on the single audio data line.
    • BCLK (Bit Clock / Serial Clock): Times the shift of audio data bits into or out of the data audio port.
In addition you can connect an input source into the blue connection on the zedboard and play a song while changing the pitches using the switches.
Note: The actual song pitches do not change, they just play together. 












Comments

Post a Comment

Popular posts from this blog

Adam Taylor MicroZed Chronicles: Interrupt Latency

Image
Continuing with Adam Taylor's tutorials in his MicroZed Chronicles on the XADC. This post relates to issue 105, which can be found using the link at the bottom of the page. What I learned from Adam's Tutorial: Interrupt Latency: The time between the interrupt being raised and the interrupt being serviced. Once a signal is in the XADC and the Zynq SoC, it is necessary to ensure that the application has been designed properly to meet the requirements and perform in the way intended. Interrupt latency plays a major role in performance.  Some issues that can impact interrupt latency are: The presence of an operating system The complexity of the ISR (Interrupt Service Routine) If interrupt latency is not considered, the application could fail depending upon the latency period, latency consistency and the time taken for the ISR. If latency is too great or ISR execution is too long, events can be missed. When this happens, it results in an unreliable system with sp...
Read more

Using the XADC Header to Read Voltages

Image
First and foremost the most important thing to specify for the XADC Header are the pinouts. Looking at the Zedboard head on, the xadc header pins correspond to the picture directly above. Vn being the pin at the top right of the xadc header. For this project we will be reading the difference between two voltage inputs within the terminal. The pins are deferentially paired and you will get the difference between Vaux8p and Vaux8n. We will be connecting Vaux8P and Vaux8N to voltages and then Vref and all three AGNDs to ground. **Note: After further investigation we found that you should only need both Vaux pins and the three AGND and it should work the same.  We created two voltage dividers to provide the input voltages for the Vaux8 pins. We ended up inputting about 0.75 Volts into Vaux8P and about 0.50 Volts into Vaux8N. Below is a picture of the outputs from within the terminal: In the terminal, Vaux8 should be reading the difference between the inputs fo...
Read more

Github

We created a Github to store our projects. SienaFPGA2017. The following link provides a helpful tutorial for using Github directly: https://guides.github.com/activities/hello-world/ *********************************************************************************** The following link provides a helpful tutorial for using the terminal to upload a project to Github: https://www.howtoforge.com/tutorial/install-git-and-github-on-ubuntu-14.04/ Some of the basics: gedit ---- Creates a file where you can copy and paste in something like a code or just write a brief description. git add ---- Adds the created files into the index git commit -m "some_message" ---- Commits changes made in the index git remote add origin "copy https from newly made github repository" ---- connects the files to the github web address git push origin master ---- Moves the files to githuhb
Read more