Category: Audio Processor

Simple 2 way crossover project

Here’s a active 2 way simple crossover project for you.

About the circuit

The Circuit is simple and uses only 3 opamps per channel.

Crossover frequency is set around 234Hz. The cutoff(crossover) frequency can be changed for your requirement. The formula for the crossover frequency indicated below:

C4 is used to block DC voltage at the input. Since the input impedance of the circuit is very low, C4 value can be as low as 0.022uF. But for my final circuit I have used 0.1uF.

R3 and R4 are voltage divider used to provide half VDD voltage for the op amps. This is required because the power supply has no negative voltage. Without this, the output will be clip on negative cycle. C3 is just a filter capacitor to clean the voltage produced by the R3 and R4 divider. R5 is used to set the input of the input buffer to half VDD, 1Meg value is used so it will have little effect on the input impedance.

Simulation

Simulation result

As expected, the crossover frequency is around 234Hz.

PCB

For PCB design, I made it single layer so most of the DIYers can easily make their own PCB. As usual I used KiCad to design the PCB which is a free software. Resistors on the VDD are just jumpers(that is why it has value = 0).

J1 – Right input

J2 – Left input

J4 – Low Right output

J5 – Low Left output

J6 – High Right output

J7 – High Left output

J3 – Power Supply (12V – 24V)

3D Render

3D render using KiCad…

DOWNLOADS:

This project can be downloaded for you own personal use. If you want to use this for commercial use, please contact me on my Facebook page for licensing. 🙂

Please don’t forget to like my facebook page. 🙂

Download page

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Digital Audio Mixer Project with ADAU1701

It has been my long desire to design a digital audio mixer but there a too little resources regarding digital signal processing. While researching I stumble upon this little chip from analog which don’t require DSP knowledge. It is program using a software called sigma studio. There is no programming language, you just need to drag and drop modules. I am still on learning process, and this is just a test of what can I able to pack on a cheap ADAU1701 DSP. Considering the price of this DSP and the size of its memory, these modules that I was able to put was amazing.

What I was able to get with the limitation of ADAU1701:

  • 8 input channels
    • all have 3 parametric equalizer
    • all have compressor
    • all have volume control
    • all have 1 pre aux
    • all have 1 post aux
  • 4 output channels
    • 2 as main output with 6 band equalizer
    • 1 as pre Aux output
    • 1 as post Aux output

That’s about it. Adding more modules will prompt an error that you are out of memory. Considering what most 8 input analog mixer are offering on the market, this features are better. This project can be further improved so I have uploaded the project file on my download page so you can edit it yourself.

Sigma Studio Project

Main Schematic

Channel strip

These controls can be accessed through a microcontroller connected to it via I2C. The microcontroller can then be connected to user interface such as buttons and displays like LCD.

10 Channel variant

I have tried to use the maximum possible inout of the ADAU1701 which is 10 inputs but simplifying the schematic and removing the compressor on channel 7 and 8. The 2 additional channel can be used for bluetooth audio. I was able to achieve the following:

  • 10 input channels
    • Channels 1-6 has HPF, 3 band Parametric EQ, Compressor, 2 aux sends
    • Channels 7 and 8 has 3 band Parametric EQ and 2 aux sends
    • Channel 9 and 10 has 3 band EQ
  • 4 output channels
    • 2 main out with 10 band graphic EQ
    • 1 Pre Aux out
    • 1 Post Aux out

I think that is the best I can have for ADAU1701 DSP.

Multi-track Recording

This is the biggest challenge for this project, for now I don’t have any idea on how can it be done and how it can work with the ADAU1701. What’s clear for now is that the ADAU1701 DSP can’t be used for this purpose. I know it can be done using the XMOS chip but the development board is too expensive for me.

Conclusion:

The ADAU1701 is a powerful DSP for audio application. It can surely be used for digital audio mixer application with limited input channels. 8 channels maybe the most channels you can have for this application. You can have as much as 10 total inputs but you need to limit some functions like compressors to be able to use all the 10 inputs or else you will ran out of memory and the project will not compile at all.

Notes:

  • ADAU1701 only have 2 ADC channels build in, you need an external ADC to be able to add 6 more inputs.

I have yet to build the actual hardware but I am not sure when I can do it. When I got the fund and time for sure but I am not sure when.

Downloads:

Download page

Arduino Controlled Bass Mid Treble and input selector

My LC75341 project was a bit of a disappointment. It was working ok but it only offers bass and treble controls. The frequency response is not that good. It has very limited controls. I decided to stop that project because it is not what I am looking for. Now after lots of research, I stumble upon this digitally controlled bass mid treble IC from ST. What is great is that it has 7 band spectrum analyzer feature and a differential input. Plus it also has Q and frequency control and a subwoofer output. This is almost exactly what I want to do.

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2 Way Active Crossover with adjustable frequency

Most of the schematic design of active crossover on the internet are mostly with fixed crossover frequency. Here’s an interesting circuit that I found on Elliot Sound Products website. I learned a lot on this website when I was just a student. If you love to build sound products such as amplifiers and tone controls, you may already know about this website.

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Arduino Controlled Bass Treble Volume and input Selector

Last time I have posted about how to control the LC75341 IC using arduino nano. And I also posted about how to modify the bass response of the LC75341 IC. This time I will be building a home amplifier for my TV, it will also feature a bluetooth reciever so that I can play via my phone.

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LC75341 Bass response modifications

Last time I have a blog post regarding on how to control the LC75341 tone control using arduino. I never really tested the performance of that IC until recently I got time to play with it. My initial impression was not good. The bass sound seems very thin and I can’t get the “boomy bass” sound that I wanted. Maybe its just me but the bass sound is thin compared to my little JBL flip bluetooth speaker. By the the way, the kit was from E-Gizmo’s digitally controlled tone control. I have investigated and model the circuit of the LC75341 tone control for simulation and the simulation results confirm what I am hearing.

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2.1 channel crossover circuit

2.1 Channel audio systems are so popular on most home sound system with low power output(usually below 50W). It only composed of left, right and a subwoofer speaker. The signal from the subwoofer is derived from both channels and filtered to output only the low frequency usually below 200Hz. Since the low frequencies are being produced by the subwoofer, it should be cut off on the main speaker.

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