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Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

freeDSP-aurora - DSP with 8 I/Os, USB Audio, S/P-DIF, ADAT, Bluetooth and Wifi contro
freeDSP-aurora - DSP with 8 I/Os, USB Audio, S/P-DIF, ADAT, Bluetooth and Wifi contro
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Old 18th February 2019, 09:34 PM   #21
dspverden is offline dspverden  Germany
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Join Date: Jun 2016
I am not sure how much gain you need for your mics, but That has some very good appnotes available about designing a front end for mic and line level inputs.
I would recommend to attach one of these designs to aurora in case you want to have mic inputs.

@all: A new version of the control app is available. You can get it here:
Release dspControl 0.9.1 * freeDSP/freeDSP-aurora * GitHub
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Old 18th February 2019, 10:16 PM   #22
Windforce85 is offline Windforce85  Poland
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Join Date: Nov 2014
Well OK, assume I would like to equalize multi-way loudspeaker using it having only mic in possession.

Is is possible to use its mic input for acquiring of impulse response generated by external measurement software via its analog output? Would it be possible to display measurement result as an dynamic overlay in order to see its changes while applying filters?
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Old 18th February 2019, 10:42 PM   #23
Pygmy is offline Pygmy  Netherlands
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Location: Haarlem
I'm very interested in room correction using FIR filters, but my lack of time and knowledge means I'd need something more than a board - I'd need it in a case with inputs and outputs so I could focus on just getting the settings right...
I guess I'll have to wait for the Kickstarter to succeed and the project to progress.
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Old 19th February 2019, 01:29 AM   #24
JayShoe is offline JayShoe  United States
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Join Date: Oct 2011
Quote:
I am not sure how much gain you need for your mics, but That has some very good appnotes available about designing a front end for mic and line level inputs.
Yeah, sorry for posting so much regarding my research on this subject. The short answer is that it's more complicated than it seems. I guess I was hoping for a low-cost high-quality solution that checks all the boxes.

I need between 20-30dB of gain.

The big takaway here is that all digitally controlled mic preamp solutions that I've found use SPI and NOT i2c... The best solution is the THAT 6266, but it is SPI and therefore would require an i2c to SPI bridge because the Aurora doesn't output the SPI required to control it. :-(

For now, I'm going to use a cheap ebay mic preamp that outputs single ended and manually connect it to the Aurora. Then I'll decide whether I want to design a better pre, or redesign the board with the PCM1865. Maybe the Aurora can also introduce an SPI header for control over the gain stages on this type configuration in the future. This would also be a reasonable solution at that point. However, still more expensive than a solution built into the ADC.

The PCM1865 incorporates the Preamp into the ADC and it's only about ~$2.25 per channel. There are no mic preamps on the market that can come that close to that cost per channel with digital control. Even the INA217 implementation (aka $5 mic preamp) doesn't have digital control, and it would be more expensive per channel than the PCM1865! If I were to do this I would probably remove the AK ADC and DAC and build my own onto the Aurora's DSP/MCU design. I suppose this would be fairly easy. I also suppose the aurora could be redesigned without the ADC/DAC altogether and just have FreeDSP Expansion connectors...

The Aurora is perfect for room correction - and really great as a building point for pro audio but not perfect.

Quote:
I'm very interested in room correction using FIR filters, but my lack of time and knowledge means I'd need something more than a board - I'd need it in a case with inputs and outputs so I could focus on just getting the settings right...
I guess I'll have to wait for the Kickstarter to succeed and the project to progress.
In all honesty the way the Aurora is designed there isn't much you have to do to connect inputs and outputs to it... I've studied the circuits and I'm fairly positive you can connect directly to the I/O of the Aurora with either balanced or single ended inputs and it will sound perfectly fine, in fact, to spec.

There are these documents detailing what I've found in regards to Single Ended>Balanced Converstions.
http://www.tij.co.jp/jp/lit/ug/tidud13/tidud13.pdf
http://www.ti.com/lit/df/tidrww1/tidrww1.pdf

Ultimately, after reviewing these documents I feel like there is no "input stage" required for single ended inputs on the Aurora. So yeah... Just attach the RCA (SE), 1/4 inch (SE/DIFF), or XLR (DIFF) jacks to wire leads, to the Aurora's analog I/O and then mount the jack to your case and you should be OK. Maybe the ESD protection would be nice to have - but still not completely necessary.

Yeah - you'd have to build your own case and solder on the leads to the jacks...
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Old 19th February 2019, 09:50 AM   #25
pelanj is offline pelanj  Czech Republic
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Hello, I have maybe a stupid question. Will this DSP support some kind of mixing matrix with aux sub busses?

E.g. I want to get three aux channels: x * (L+R), R - x * L, L - x * R and then apply a highpass on each of these channels and send to outputs. Then, I would have the L+R signal with lowpass for mono subwoofer. Each of the outputs would also contain some EQ for e.g. compensating CD or dipole response.
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Old 19th February 2019, 11:26 AM   #26
JayShoe is offline JayShoe  United States
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Quote:
Hello, I have maybe a stupid question. Will this DSP support some kind of mixing matrix with aux sub busses?

E.g. I want to get three aux channels: x * (L+R), R - x * L, L - x * R and then apply a highpass on each of these channels and send to outputs. Then, I would have the L+R signal with lowpass for mono subwoofer. Each of the outputs would also contain some EQ for e.g. compensating CD or dipole response.
I don't really understand your three aux channels example. However, I can say that SigmaStudio is a GUI designed to allow you to create audio flows visually. The Aurora has 8 aux inputs which would allow you connect your CD Player to 2 of those 8 channels. You can also stream high quality USB Audio to the device. In the future we'll probably be able to send Bluetooth Audio or Wifi Audio to the DSP as well (software not developed yet for Wifi/Bluetooth Audio). Then inside the software you can route those input channels into whatever flow you want. The DSP will allow you to create a "matrix" that sends, sums, processes, monitors, or splits signals to whatever output you want.

L/R (CD-Player) -> Aurora ADC Inputs -> Sigma Studio
THEN
L + R -> lowpass filter -> Aurora DAC Outputs -> Mono Sub Output
L -> highpass filter ->Aurora's DAC Outputs -> Highpass L out.
R -> highpass filter ->Aurora's DAC Outputs -> Highpass R out.

Plus you'll have 6 inputs and 5 outputs to spare... And yes SigmaStudio with the ADAU1452 has plenty of processing power to handle this and it has highpass and lowpass algorithms setup already.

This is the Free software that the Aurora is designed for:
SigmaStudio | Analog Devices

A Youtube Video describing the software:
YouTube

Last edited by JayShoe; 19th February 2019 at 11:31 AM.
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Old 19th February 2019, 12:21 PM   #27
JayShoe is offline JayShoe  United States
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Join Date: Oct 2011
Here is a first take on a schematic for single ended RCA inputs. One board will work for both inputs and outputs, I believe. Please critique. Thank you.

freeDSP-aurora - DSP with 8 I/Os, USB Audio, S/P-DIF, ADAT, Bluetooth and Wifi contro-freedsp-aurora-rca-inputs-2019-02-19_0723-png
Attached Images
File Type: png freeDSP-aurora-RCA-inputs-2019-02-19_0723.png (72.7 KB, 655 views)
Attached Files
File Type: pdf freeDSP-aurora-RCA-inputs-2019-02-19.pdf (22.9 KB, 23 views)

Last edited by JayShoe; 19th February 2019 at 12:24 PM.
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Old 19th February 2019, 12:50 PM   #28
pelanj is offline pelanj  Czech Republic
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I forgot to add a link I wanted to add: http://elias.altervista.org/html/Sin...kerStereo.html

I would need to feed some combinations of L+R and L-R into different speakers - at least 3 but maybe more (there is plenty of outputs). As long as I can do this in the Sigma Studio, then I am happy - I will check the documentation. Thanks!
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Old 19th February 2019, 09:29 PM   #29
dspverden is offline dspverden  Germany
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Join Date: Jun 2016
Yes you can do that with SigmaStudio.

You can always use SigmaStudio to add features that are not supported by the default software.

But let me tell you a secret: Software variants adding additional features will be added to the git repository in the future.
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Old 20th February 2019, 02:50 PM   #30
JayShoe is offline JayShoe  United States
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Join Date: Oct 2011
I went into the freeDSPx AnalogIO x8 board and found the "ESD Protection" circuit.

Here is the Aurora:
freeDSP-aurora - DSP with 8 I/Os, USB Audio, S/P-DIF, ADAT, Bluetooth and Wifi contro-freedsp_aurora_input_schematic-png

Here is the AnalogIOx8 (with the extra parts):
freeDSP-aurora - DSP with 8 I/Os, USB Audio, S/P-DIF, ADAT, Bluetooth and Wifi contro-freedsp_analogiox8_input_schematic-png

Here is my second take on a schematic for single ended RCA inputs.
freeDSP-aurora - DSP with 8 I/Os, USB Audio, S/P-DIF, ADAT, Bluetooth and Wifi contro-freedsp_aurora_io_rcax8_schematic-png
Attached Images
File Type: png freeDSP_Aurora_Input_Schematic.png (33.1 KB, 624 views)
File Type: png freeDSP_AnalogIOx8_Input_Schematic.png (44.4 KB, 611 views)
File Type: png freeDSP_Aurora_IO_RCAx8_Schematic.png (28.5 KB, 605 views)
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