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Old 14th March 2013, 09:53 PM   #41
1audio is offline 1audio  United States
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I said it was a crude sketch. Ideally the clocking would be an isolated subsystem with an independent supply and transformer coupled outputs.

The Capture/recording process is fundamentally different from the playback process in a few ways. In playback the file already exists and has sample rate bit depth etc. defined by the file. In recording, the user defines all of those based on a number of aspects, many of which cannot be predicted. These include target use, distribution medium, standalone or part of a different work that needs to be mixed etc. While it may be convenient to select from a computer it can be just as easy to set switches on a box, typical of many premium recording interfaces.

A sound interface with an spdif input will need to sync to the external source, by definition. The internals are usually a receiver chip like this: http://www.asahi-kasei.co.jp/akm/en/...k4116_f03e.pdf which can detect the incoming sample rate (I would use the crystal version for this, not the decode of the header, which is often wrong). I believe most of the USB audio drivers can handle the sync, its effectively the same as async operation. The chip can report to the interface what the incoming sample rate is. We will need Alex's help (unless you want to figure it out) how to get the info and pass it upstream.
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Old 15th March 2013, 12:26 AM   #42
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
To keep life simple and end up with reusable blocks I would use an SPDIF-AES interface on the ADC and not bother with computer control. None of the software I know of can control the ADC automatically (except for the Juli@ in XP on Praxis). The Windows sound engine makes it a mess. Just use manual controls, which is how you would use it for a recording interface. Adding a Toslink output as well is trivial so why not?

However if we can get someone to figure out using a pic/arduino/etc. to control the ADC from a serial port equivalent that has attractions.

In measuring I usually get it all working at 192K and leave it. Digital measurements can benefit from other sample rates but the analog stuff really doesn't.

If the ADC box has a switch with 6 positions for sample rate and an internal-external clock switch I would consider it done for now. A separate control for input sensitivity is important and the issue of calibrated input is something to address. This is where a really stable low distortion oscillator comes into play with a known output level. Although it could even be a square wave counted down from the master clock and still have a known peak value pretty easily (a la Praxis).
I already have a PIC set up for control via USB OTG with a crude but workable windows interface. The PIC can control what ever you want. It wouldn't take much to do something that looks fairly decent for a control panel. The PIC can handle the calibration of the ADC as well.
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Old 15th March 2013, 12:45 PM   #43
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Quote:
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I already have a PIC set up for control via USB OTG with a crude but workable windows interface. The PIC can control what ever you want. It wouldn't take much to do something that looks fairly decent for a control panel. The PIC can handle the calibration of the ADC as well.
Ah, ok, I think I understand a little more now. You need the controller because you want to be able to control sampling rate and other things from the computer and not via mechanical switches.
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Old 15th March 2013, 01:53 PM   #44
davada is offline davada  Canada
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Yes. I hoping for a neat little package you can plug into a laptop and go.
It's ok to have a few buttons/switches on a physical front panel but I want to get away from all that wiring.
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Old 15th March 2013, 01:59 PM   #45
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Yes. I hoping for a neat little package you can plug into a laptop and go.
It's ok to have a few buttons/switches on a physical front panel but I want to get away from all that wiring.
That's funny because me being a mechanical engineer, I want all those toggles and rotary switches...

It's fine what ever you come up with. I'm sure it will be great.
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Old 15th March 2013, 02:17 PM   #46
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
I said it was a crude sketch. Ideally the clocking would be an isolated subsystem with an independent supply and transformer coupled outputs.

The Capture/recording process is fundamentally different from the playback process in a few ways. In playback the file already exists and has sample rate bit depth etc. defined by the file. In recording, the user defines all of those based on a number of aspects, many of which cannot be predicted. These include target use, distribution medium, standalone or part of a different work that needs to be mixed etc. While it may be convenient to select from a computer it can be just as easy to set switches on a box, typical of many premium recording interfaces.

A sound interface with an spdif input will need to sync to the external source, by definition. The internals are usually a receiver chip like this: http://www.asahi-kasei.co.jp/akm/en/...k4116_f03e.pdf which can detect the incoming sample rate (I would use the crystal version for this, not the decode of the header, which is often wrong). I believe most of the USB audio drivers can handle the sync, its effectively the same as async operation. The chip can report to the interface what the incoming sample rate is. We will need Alex's help (unless you want to figure it out) how to get the info and pass it upstream.
It's faster to get expert help. I have to learn all this and that takes time. I,m quite willing to learn it all this. Up to now I really haven't been been interested and I have a bit of catching up to do. I get lost in the terminology a bit. USB audio is different.

From what you describe I believe the TI parts do the same detection. But what part we use doesn't matter as as it does the job.

Just to get things going, I'm going to try to do the mixing in a PIC and see if it can keep up. I think it probably can if that's all it's doing.
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Old 15th March 2013, 02:42 PM   #47
davada is offline davada  Canada
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That's funny because me being a mechanical engineer, I want all those toggles and rotary switches...

It's fine what ever you come up with. I'm sure it will be great.
Fine we'll do both. I thought you worked in a patent office.
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Old 15th March 2013, 03:45 PM   #48
1audio is offline 1audio  United States
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Careful what you ask for. Mechanical switches are great except when there are two pathways to the selection. Mechanical switches indicate their settings directly. if there is a remote pathway then the switch settings can get overridden and you don't know what the settings are. Usually this is dealt with using buttons and indicators, which I think are fine, but the process gets more complex quickly and 2-3 rotary switches became a row of buttons and lights with drivers and more involved mechanicals etc.

The other issue is the power for the PIC (or whatever) and the noise generated by the PIC. There are techniques for reducing/eliminating these issues but they also bring complexity.

What I would like is a simple logic decode from the essential switches: sample rate, clock source, that can control the ADC. There are really only two practical candidates, the TI PCM4222 and the AKM AK5394A I think. The ESS is unknown and the ARDA seems to be a myth. If there are others it would be interesting to know. This would make it possible for a single PCB to support both I believe.
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Old 15th March 2013, 04:13 PM   #49
borges is offline borges  Norway
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The Audio/SDR-Widget project already has an MCU and a host software (WidgetControl) which can be expanded to provide both GPIO and computer control. It should be possible to run the control program in low-priority tasks. I don't know the SDR widget user interface, anybody care to elaborate on what's already in place?

Having multiple programmable devices in one box will be a hassle.

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Old 15th March 2013, 05:05 PM   #50
RNMarsh is offline RNMarsh  United States
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Since this instrument is for testing audio equipment.... we can make some educated guesses about some settings and make them default. Then what is left to deal with is a minimum if anything at all.
Dont make it very flexible in other words and have all the defaults pre configured (software or hardware switches or both). personally, I dont want to use anything that requires me to know anything about the internal workings...... let the instrument do all the work and no thinking on my part. I only want features like zoom or range changes on freq and levels on the displayed graph/plot. Sample rates et al need to be default or auto-detected.
Later you can add-in options in a drop down menu to change default settings.

Anything done along these lines makes it a useful tool for all....

Thx-RNMarsh

Last edited by RNMarsh; 15th March 2013 at 05:09 PM.
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