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Old 29th March 2009, 08:42 AM   #31
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Hi EUVL

Quote:
How about user interface (display, remote, ....) ?
And when would you be offering to us ?
At the moment the prototype is controlled by a serial interface (for testing), so no keyboard or display yet.

We plan to use two double blue 7-segments LED displays.

The first display shows the CD number (1 ... 99), the second shows the track number (1 ... 99). These displays are also used for other information like shuffle play, and SD-card number.

There will be two keys for CD selection (- / +), two keys for track selection (- / +), a key for stop, and a key for play / pause.

The player will also have a serial communications channel, it can be used for remote-control functions.


But first we need to have a version that runs on most SD-cards (even the slower one's) without causing drop-outs.

In order to achieve this, we plan to use Philips I2S interface with 32 bits / frame (2 x 16 bits). This will double the effective RAM ping-pong buffer size to 1 K byte.
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Old 29th March 2009, 04:25 PM   #32
EUVL is offline EUVL  Europe
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John,

I think SD cards will only get larger and faster, so there is perhaps not much point in trying to support the smallest and slowest ones.

The proposed operating keys are sufficient for a minialistic player, but IMHO a 2x8 VFD display or blue LED dot matrix (probably not available ?) is perhaps better if playing time can be displayed. Or is it a limitation of the dsPIC ?

And how about fast forwards and backwards within the same sound track ?

Are USB-sticks an alternative to SD cards ?

Pls keep us posted.


Thx,
Patrick
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Old 29th March 2009, 05:09 PM   #33
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Hi EUVL,

Quote:
The proposed operating keys are sufficient for a minialistic player, but IMHO a 2x8 VFD display or blue LED dot matrix (probably not available ?) is perhaps better if playing time can be displayed. Or is it a limitation of the dsPIC ?
The display will produce interference, the main objective is best possible 44.1/16 playback imaginable, meaning extreme low interference levels and extreme low master clock jitter.

However, the integrated RS232 communications channel can be used to control and read SD-card player status. The serial interface will have to use optical interface (with PC) in order to completely avoid ground loops, we are planning to use 2 x Toslink for this. If desired, artist name, Album and artwork can be displayed on a connected computer.

I attached a photograph of the SD-card player prototype (before improvement). Turned out that the drop-outs were caused by both the SPI clock frequency and long wires running to the SD-card.

The SD-card prototype is now modified (much shorter wires), and now it plays flawlessly for hours.

Although it was not causing the problem, I2S format is now 32 bits/frame, and the bit clock equals 1.4112 MHz.


Quote:
And how about fast forwards and backwards within the same sound track ?
This isn't implemented yet, might be added later if it doesn't affect performance in any way.
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Old 29th March 2009, 05:17 PM   #34
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Here is a photograph of the modified SD-card player prototype in action (stand-alone with debugger disconnected), it runs on a USB power supply and uses a TDA1543 for testing
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Old 29th March 2009, 07:40 PM   #35
EUVL is offline EUVL  Europe
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Looks good. Thanks for the photos.

> the main objective is best possible 44.1/16 playback imaginable, meaning extreme low interference levels and extreme low master clock jitter.

Could not agree more.


Patrick
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Old 29th March 2009, 07:40 PM   #36
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Hello John

Have you try those mp3/wav players that has a digital out and used SD card ?

Like the iRiver iHP-120.

I was thinking of using a player like that, using it with a non-os TDA1541A dac, but it maby less good since it is SPDIF.

Bye

Gaetan
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Old 30th March 2009, 07:48 AM   #37
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Hi UV101,

Quote:
Could a Squeexebox be used to output I2S?
Yes, I already tried this using an older model squeezebox, it required some glue logic though. I attached a photograph showing the tapped I2S signals from the SB being connected to a DI16 DAC (16 x TDA1543).

One problem is the network connection that introduces an ac ground-loop, the other is the high jitter produced by the squeezebox on-board master clock, so some more mods are required. There is also the ground-loop introduced by connecting the DAC (with built-in power supply) to the squeezebox (with built-in power supply). Finally It required a computer, running the Slimserver database.

I often had problems with the squeezebox player connecting to the database as well, this was very annoying. With increasing amount of stored CD images, it also became increasingly difficult to locate the desired CD / track, using the SB user interface, so finally I stopped using it.

Next I started using the mac with iTunes, now music was much easier to access. I started with an USB audio interface, but the galvanic connection created a ground-loop, and sound quality wasn't satisfying. So I built-in opto-couplers (before reclocking) in order to interrupt the ground loop. This produced slightly better results, but still wasn't optimal.

Then I switched to Toslink, first using an analogue PLL driving a VCXO master clock. This was later replaced by a micro controller-based VCXO FLL that synchronously reclocks the source timing signals. Problem was, my CD player produced better sound quality (Toslink) than the Toslink output on my mac. The problem seemed to be solved when I started using the Airport Express mini Toslink output (fixed 44.1/16).

As DAC sound quality kept improving, due to modifications, this option also didn't seem to be perfect. The audible differences between both CD player digital output and AE digital output kept increasing with DAC performance.

That was the time I started looking for a better solution (perfect digital audio source) that should solve these "issues" once and for all. This lead to SD-card player development.

Quote:
Whilst the media os not solid state, has no mechanical and servo parts which I think is the point of this thread??
The point is to create an (almost) perfect digital audio source that is as compact as possible, consumes as little power as possible, provides extreme low masterclock jitter, I2S output, and lowest possible interference levels. In order to eliminate ac ground loops, no galvanic or capacitively-coupled interlinks to any (computer) equipment is allowed. Wireless communication like WLAN is not an option either, as it causes significant EM interference.
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Old 30th March 2009, 07:51 AM   #38
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Quote:
Originally posted by -ecdesigns-
Wireless communication like WLAN is not an option either, as it causes significant EM interference.
Significant even through metal shielding?
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Old 30th March 2009, 08:11 AM   #39
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Perhaps you should have tried a "quality" Toslink output as it is used on pro-soundcards

My current preference:
As you know I use an optical USB Cable from Opticis (USB 1.1 only) for galvanical isolation.
The receiver is "custom-made" battery powered. This made a great improvement
with your USB reclocker/receiver I used to use.
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Old 30th March 2009, 08:11 AM   #40
phofman is offline phofman  Czech Republic
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Quote:
Originally posted by -ecdesigns-

...One problem is the network connection that introduces an ac ground-loop ...
By AC ground loop do you mean the coupling via ethernet isolation transformers?
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