Author Topic: Integrated audio DSP with free tools?  (Read 125 times)

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Integrated audio DSP with free tools?
« on: November 13, 2017, 02:57:32 AM »
I'm afraid of the post is an off topic in this forum. :-[Maybe not.
As a hobby project I'm building an audio amplifier. It'll be the amp for my "home theater". I only have a small room so there's no room for 5.1 speakers. And honestly I don't care for 5.1. So I want just a small stereo system with a mono subwoofer, or as they call it, a "2.1" system.

I have decent speakers, (Yamaha NS-50F pair, rated at 80W), and a subwoofer I built myself. Testing has shown that an LM3886 (68W max @ 4 ohms) is more than enough to drive it. So I went ahead and built a simple, triple amplifier.

The results were disappointing. Not even remotely enough "bass". So I built a small "bass boost" circuit (more like a "treble cut" and raise the volume). It was a lot better. But I missed the EQ.

I would like to build an EQ. An analog one would be relatively simple to build with a bunch of opamps. I want this controlled by a remote control so I'd have to replace the pots with digipots. But it starts getting complex, as I'd need:

Input stage/buffering
Low-pass filter for sub
Output preamp (LM3886 needs to be driven relatively high)
This is rather complex, too many ICs involved. Layout becomes critical, opamp noise starts adding up... and I'm simply not that good at analog electronics.

So I thought of just using a DSP. I'm more or less familiar with these as I've played with FIR and IIR filters in the past. Building an audio EQ and output multiplexer (stereo to 2.1) with a DSP would make things a LOT easier, less noisier and overall (in my opinion), better. Well, except maybe for ADC-DSP-DAC delay.

Is there a solution that has:

High quality (high SNR, low distortion) ADC with at least 24bit/96khz
At least 32-bit DSP core (floating point prefered?)
High quality (SNR, dist) DAC.
FREE development tools, or at least, unrestricted trial versions.
Comes in an easy to manually solder package (not QFN or BGA. QFP is fine)
Bonus features:

Extra inputs such as S/PDIF, I2S, etc. And multiple analog input channels (to save on the input multiplexer).
It's available as a cheap "ebay board"
I've found several options but not one that fully meets all these requirements. TI is not very helpful (their audio DSP site seems broken). Analog seems to charge $5000 for their software, and the "trial version" only supports one part. Cirrus Logic needs me to "contact my local sales office" to download their development software.

Seems so far the only realistic option is to just use an audio CODEC and a 32-bit microcontroller such as STM32F4.
Thanks all.


Re: Integrated audio DSP with free tools?
« Reply #1 on: November 13, 2017, 06:31:18 AM »
Have a look at the Axoloti board. It's got basically what you suggested, codec+STM 32-bit chip. Plus all the hardware is done for you, and there's a good community around it. There's even a GUI-based environment for building effects, so you never know, there might well be a EQ you could use for a start.



Re: Integrated audio DSP with free tools?
« Reply #2 on: November 14, 2017, 07:29:34 PM »