PROPOSAL: wireless digital loudspeaker with remote volume and on/off control - Page 3 - diyAudio
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Old 28th July 2013, 06:08 AM   #21
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Join Date: Mar 2007
Location: California
With the user interface more or less worked out on the Arduino, I decided to build up a test circuit for my input switcher on a breadboard. Even though it is a bit of a rats nest, it works - at least I can get SPDIF to run through it at 48kHz. The multiplexer IC that I am using has an enable pin, and I can change the state of that to mute the system without having to generate an "all zeros" SPDIF signal. Very convenient.

Tomorrow I check that 192kHz will pass through unscathed. Then I need to add code to the Arduino to set the pins that control the multiplexer so that I can test its input switching functionality. I don't expect any issues there.

After that I will need to test out the volume control circuitry. There is a thread around here somewhere on that already:
NEED ADVICE: controlling Mini2x4 volume when using digital inputs

So far this project is looking promising!

-Charlie
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Old 28th July 2013, 09:23 PM   #22
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Join Date: Mar 2007
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I tested out the input switcher at a few different sample rates - the highest that it will pass is 96kHz. But in another forum thread, someone pointed out to me that the stray capacitance and contact resistance of a breadboard tend to cause circuits that have signals above a few MHz not work, and this is probably the case with my little hack job:

Click the image to open in full size.

I'll have to transfer the circuit over to a prototyping PC board where everything can be soldered down, component leads trimmed, etc. and then retest it.
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Old 9th December 2013, 01:16 AM   #23
Dresden is offline Dresden  Czech Republic
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Default Interesting Project

What is the present state of the project?

I have for quite some wanted a system which can send separate signals to powered speakers.

In the last few days, I resumed my search, and not finding anything comparable, I had resolved to making a list of potential retail components (such as the SONOS product), for possible use in sending a signal to two powered loudspeakers. (I also only want a power cord for each speaker, nothing more.)

If you can design something which can match the performance of the SONOS (albeit at a more affordable price) in the foem of a module for DIY/OEM, I am interested. (Perhaps you have already accomplished such?)


Quote:
Originally Posted by Charl
3576854
I tested out the input switcher at a few different sample rates - the highest that it will pass is 96kHz. But in another forum thread, someone pointed out to me that the stray capacitance and contact resistance of a breadboard tend to cause circuits that have signals above a few MHz not work, and this is probably the case with my little hack job:

Click the image to open in full size.

I'll have to transfer the circuit over to a prototyping PC board where everything can be soldered down, component leads trimmed, etc. and then retest it.
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Old 15th July 2014, 07:36 PM   #24
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Join Date: Mar 2007
Location: California
Quote:
Originally Posted by minidsp View Post
That's a neat idea Charlie. Keep us updated on your progress...
We don't have any wireless audio solution so providing your system works, we can certainly build a section of our website to advertise your final tweak.

Keep us updated.
OK, at last I can offer an update.

First, my apology that this project became a little stale. I have been wrestling over how to implement the volume control and remote on/off, etc. I needed to design and build some custom circuitry for this in addition to the digital input selector. This is where I got bogged down - I just could not convince myself of a "best" way to do it. I designed and simulated various circuits, but these always left me scratching my head about how they would perform or fall short, etc. I even went as far as to purchase a bunch of ICs and other parts, but then it hit me...

To send SPDIF using the AV wireless senders you are limited to a sampling rate of 48kHz. This is because the bandwidth capability of the RF wireless circuitry (that is normally used for analog video) is not high enough to accommodate a higher sampling rate. But often people have SPDIF sources at other (higher) rates, and to make sure that these sources can be sent using the wireless system the digital signal must first be downsampled to 48kHz. After some Q&A with the MiniDSP DevTeam, I discovered that their miniDIGI can be used as an ASRC, and its output stream is always at 48kHz. Great! As a bonus, the miniDIGI has built in input selection from its four spdif inputs (two coax, two Toslink) although you have to add a MBB switch to automate this. No prob. So I picked up another miniDIGI (once they were back in stock) so that I could use it in this capacity at the source. This is in addition to the two other miniDIGI boards that are used as spdif receivers for the 2x4 boards I will put in my loudspeakers.

The ah-ha moment that I had recently was about the 2x4 + miniDIGI stack. Thanks to the flexibility of these products, you can not only route the incoming spdif stream from the miniDIGI to the 2x4 (this is the normal usage) but you can also route a pair of processed channels from the 2x4 (e.g. the 2x4 outputs CH1 & CH2) back to the SPDIF output of the MiniDIGI. Because the 2x4 has the capability of using an external potentiometer for master volume control this gives us the possibility, with the addition of one more 2x4 board, to route the spdif stream to the 2x4 so that its master volume control can be used. This setup makes it possible to adjust the volume of the signal digitally before it is sent over the wireless system rather than at the loudspeakers using my previous control circuitry concept. This has several advantages...

It's been noted that when using the external volume pot, the volume = max position results in a gain loss of about 3.3 dB when using the onboard voltage source (3.3Vdc) on the potentiometer header for the 2x4. With my setup, I can make up this loss by programming a boost into the "crossover" section using the advanced biquad mode. But there is another advantage: I have often complained to the DevTeam about the lack of input PEQ/biquads in the 2x4 and 4x8 products. I use these to flatten the frequency response of my loudspeakers instead of the PEQ bands for individual drivers, which has certain subtle but important advantages. The "input" PEQ bands are globally applied to all channels in the crossovers, which are downstream. Since we have added another 2x4 board to control the volume, we can use its PEQ biquads for global PEQ as well, and this increases the number of available global PEQ "bands" by 8+6 = 14 bands! Awesome!!! My prayers have been answered.

I have been testing the volume control setup over the last couple of days. I had to iron out a couple of odd problems with the plug-in, but it seems to be working great now.

There is another advantage of this setup over my previous volume control scheme: you can connect as many wireless receivers to the system as you would like and they will all get the same volume controlled digital signal. This makes it possible to mix digital crossovers (e.g. the 2x4+miniDIGI stacks that I will use in my main loudspeakers) with analog crossovers by simply connecting the wireless receiver to a DAC feeding the analog crossover. For instance, you may only need a relatively simple crossover for a subwoofer and don't need all the processing power available with a 2x4. You could have multiple subwoofers located anywhere you would like throughout the listening space as long as they can be connected to mains power, without having to run any signal cabling. This would make it possible to investigate distributed subwoofer setups such as those espoused by Geddes:
Serious Audio: Two Great Articles on Multiple Subwoofers by Dr. Earl Geddes
I plan to do this kind of thing using four identical subs that I am building. These will be powered by plate amps that have their own built in analog LP crossovers, so there is no need for any DSP. This situation is likely quite common with plate amp powered subwoofers, so its likely to be a useful tip for others as well.

Finally, one significant advantage of the wireless SPDIF bridges is that they eliminate long and/or multiple cabling runs. These can be a source of noise pickup and can result in ground loops and other very undesirable effects. I have definitely encountered these in the past when running multiple 10-foot-long line level cables between a MiniDSP crossover and the amps located in my powered speakers. It was pretty amazing that when I would pick up and separate the cables I could form a very nice antenna that easily picked up AC hum present in the room! By eliminating cable runs between equipment this kind of problem should no longer be a concern.

When I finally manage to get my nascent system fully working (likely this will take a little while) I will post all the details of the setup for those who want to assemble something similar.

-Charlie
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