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SigmaDSP Processors and SigmaStudio Development Tool
  • Processors and DSP
SigmaDSP Processors and SigmaStudio Development Tool
Documents Thoughts on using index selectable filters...
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SigmaDSP Processors and SigmaStudio Development Tool requires membership for participation - click to join
  • Documents
  • 96 kHz operation for ADAU1452 serial ports
  • ADAU1701 Input and Output Signal Routing
  • ADAU1701: ADC resistor values for higher sample rates
  • Booting a SigmaDSP from a microcontroller with no C compiler
  • Calculating Filter Coefficients to Store in a Microcontroller
  • Can ADI provide or support the USB interface firmware code for my self-assembled PCB or end product?
  • Can ADI provide or support the USB interface firmware code for my self-assembled PCB or end product? - 2
  • Can I program multiple SigmaDSPs in parallel using one USBi?
  • Can I use SigmaDSP to decode MP3/WAV/AAC?
  • Can SigmaDSP do frequency-domain processing like FFT or pitch shift?
  • Can the ADAU1772 be used with a TDM output stream that has an odd number of channels?
  • Compressor Table Format - Changing compressors at run-time
  • Creating a delay after startup
  • Creating a simple balance crossfade control
  • E2PROM Selfboot problem
  • Empty Cells
  • EVAL-ADAU144XEBZ Evaluation Board Schematics
  • EVAL-ADAU1781Z GPIO Mapping in SigmaStudio
  • EVAL-ADAU1781Z GPIO Mapping in SigmaStudio - 2
  • Example Project: Using the Stopwatch to Count Successive Samples over a Threshold
  • Excluding Cells from the Exported System Files
  • FAQ: After downloading self-boot code to my target EEPROM, my USBi isn't recognized anymore by my computer. What's wrong and how do I fix it?
  • FAQ: Can I write C or assembly code for SigmaDSP in SigmaStudio?
  • FAQ: Can we bundle SigmaStudio with our product design?
  • FAQ: Developing custom algorithms and/or using 3rd party algorithms
  • FAQ: How can I change parameters on-the-fly in an application without SigmaStudio?
  • FAQ: How can I estimate MIPS/Memory resource on SigmaDSP?
  • FAQ: How do I change the sample rate of my SigmaStudio system?
  • FAQ: What operating systems are supported to run SigmaStudio?
  • FAQ: What types of capacitors are good to use in the analog audio signal path?
  • FAQ: Where can I send my questions I don't want to post in a public forum?
  • FAQ: Why can't I control any of the knobs or sliders in my SigmaStudio project?
  • FAQ:  Can I have multiple versions of SigmaStudio installed simultaneously?
  • FAQ:  Where can I download SigmaStudio?
  • FAQ:  Where can I find a description of the changes made in the latest version of SigmaStudio?
  • FAQ:  Which SigmaDSP ICs support selfbooting from an EEPROM?
  • FAQ:  Why isn't a software/documentation CD included with my evaluation board?
  • How are the audio inputs routed in SigmaStudio's Input cell?
  • How do I create the microcontroller code to interface to my SigmaDSP?
  • How do I execute a software safeload write?
  • How do I implement external volume control using GPIOs or Aux ADCs?
  • How do I report a SigmaStudio bug?
  • How do I start a timer after power-on, or when the input signal goes away?
  • How do I use a GPIO button to select different audio processing paths?
  • How many instructions can be executed per sample in SigmaDSP?
  • How to avoid distortion or clipping on the ADC inputs for the ADAU144x evaluation board
  • How to avoid distortion or clipping on the ADC inputs for the ADAU144x evaluation board - 2
  • How to calculate index table values in 28.0 format
  • How to create a crossover with more than 3 bands
  • How to self-boot the EVAL-ADAU1401AEBZ (evaluation board for ADAU1701, ADAU1702, and ADAU1401A)
  • How to self-boot the EVAL-ADAU1701MINIZ (evaluation board for ADAU1701, ADAU1702, and ADAU1401A)
  • Implementing Safeload Writes on the ADAU1701
  • Memory requirements for booting a SigmaDSP with a microcontroller
  • Monitoring average and instantaneous signal levels
  • My 2IN4OUT Proto with SPDIF based on ADAU1701
  • My IIR filter is outputting a value, even when the input goes to zero. Is this a bug?
  • New Sigma300 Family Products:  ADAU1451 & ADAU1450
  • New SigmaStudio 3.3 Beta Version Available
  • New SigmaStudio Download Site
  • Peak Full Range Compressor
  • Playing audio samples in SigmaDSP
  • Preserving "Ear-candy" in a mono mix
  • Problems with Push Button Volume w/Mute module
  • Setting the PLL mode for the ADAU1701 at different sample rates
  • Sigma 300 (ADAU145x) Exponential Slewing
  • SigmaDSP PCB Layout Best Practices
  • SigmaDSP Products and Evaluation Boards - ROHS and REACH Compliance
  • SigmaStudio 3.4 Released
  • SigmaStudio consulting services...
  • Slow rate random number generator
  • Stimulus-Probe Capability and Limitations
  • Testing USB communications between the PC and SigmaDSP
  • The ADAU1372 is not on the list of compatible processors or under Processors/DSPs on Sigmastudio 3.11.1 or 3.11. Can you please tell me how I can use the EVAL board with ADAU1372?
  • Third Party Algorithm Plugins in SigmaStudio
  • Thoughts on using index selectable filters...
  • True peak-to-peak detection in SigmaStudio
  • Truncating bits using bitwise logic
  • Updated self-boot EEPROM image generation / download
  • Updating SigmaDSP Parameter with a Microcontroller
  • Using compressors to avoid output clipping
  • Using hardware data capture (trap) registers with the DSP Readback cell (AD1940, ADAU1701)
  • Using stopwatch with feedback loop to create periodic test signal
  • Using the ADAU145x's Slew Ext Volume Block
  • Using the DSP Control mode of the ADAU1761 PGA / ALC
  • Using two SigmaDSP evaluation boards simultaneously with one USBi board
  • Welcome to the SIGMADSP Processors and SIGMASTUDIO Development tool community
  • What are the mute ramp times in the AD193x codecs?
  • What are the number formats for SigmaDSP?
  • What is the step size for audio delay in a SigmaDSP?
  • When should I use single precision or double precision filters?
  • Where can I buy a SigmaDSP Evaluation Board or USBi (EVAL-ADUSB2EBZ)?
  • Which SPI Mode is used by SigmaDSP Devices?
  • Workaround: Creating constant-dB envelope decay using an existing linear decay algorithm
  • [bug report] False frequency response displayed in a parametric equalizer window for an IIR coefficient filter
  • [Tutorial] Using Hierarchy Boards to create re-usable code

Thoughts on using index selectable filters...

I recently was working on an ADAU1701 project where I wanted to select from multiple possible filter banks. My first approach was to create multiple filters in the project, split the audio signal to go through all of the filters, and then select the desired output using a multiplexer. While this approach worked, it required a lot of program instructions. In fact, it was filling up the entire program memory!

Here's a simple example illustrating this approach:

Unfortunately, using branched filter banks will drastically increase the number of instructions executed in a program, even though only one filter bank is being used at any given time. Here's the reason why:

The ADAU1701 SigmaDSP is a steam-based processor. It has a deterministic program counter. The program counter always steps through from the beginning of the program to the end of of the program. This happens on every sample. When the SigmaStudio project is compiled, all of the algorithms in the project are converted into program instructions and are assigned a location in program memory. This happens regardless of whether the actual audio path for individual algorithms is being used at any given time.

This means that all algorithms will occupy space in program memory, and since the program counter is deterministic, every instruction will be executed on every frame of the program. As a result, in my example above, both filters will be executed every time the program loops, even though only one output path is being used. That's simply the nature of the SigmaDSP core architecture.

So, how can I get multiple filters in parallel, and only select one set of filters at a given time? The solution to this problem is to use index-selectable filters.

Because of the nature of the SigmaDSP architecture, it is wasteful to put multiple sets of filters in the project if only one path is going to be used at any given time. So, my first approach was not the best way of solving the problem. In this case, instead of creating multiple "instances" of the filters, it is better to create a single "instance", and to store multiple sets of filters in memory instead. This is usually much better from a resource perspective, since parameter memory is more abundant than program memory.

Here is an example of an algorithm in SigmaStudio that implements a single "instance" of a filter and allows users to store multiple sets of parameters for that filter: https://wiki.analog.com/resources/tools-software/sigmastudio/toolbox/filters/general2ndorderindexselectable

The red index input pin for this cell selects a single set of filter coefficients from the different options in memory. This way, only one filter is executed per audio sample, but multiple options for the filter coefficients are stored in memory.

If one filter is not enough, then there is another option in the SigmaStudio library that allows users to store entire banks of filters that can be recalled using an index. The IdxSelectable Indp. Multiple Band Filter is a great example:

https://wiki.analog.com/resources/tools-software/sigmastudio/toolbox/filters/idxselectableindpmultiplebandfilter

Here is an example implementing this approach:

This implements the same functionality as my original approach, but uses fewer program instructions!

If you want to learn more, here are some more resources...

  • Filter examples, including index filters: https://wiki.analog.com/resources/tools-software/sigmastudio/tutorials/filterexamples
  • EngineerZone thread showing how to select EQ presets with GPIOs:  http://ez.analog.com/thread/14552
  • Application note including an example of an index-selectable filter: http://www.analog.com/static/imported-files/application_notes/AN-951.pdf
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