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Re: [Xylo-SDR] Saxo


Hi Phil,

Thanks for the comments.
In order to avoid the problems caused by non-synchronized clocks, I am considering resampling the PC soundcard audio input and output (which will be running at a lower sampling rate) using a fractional FIR decimator and interpolator. I still need to look closer at the problem and see how easy or complex it is.
One reason I have purchased the Saxo is that I could use 2 ADs and 2 DAs and avoid all the problems you have mentioned. However, VHDL or Verilog are obstacles for me at the moment. Verilog looks a bit familiar due to its C-like syntax, but I need to dedicate some time (the most scarce resource at the moment) to learn it enough to be able to do something useful. 

73,

-- Edson


Phil Harman wrote:


Hi Edson,
Your project sounds very interesting. Just one thing to be aware of. If you use an external A/D converter as input and a sound card for output then unless the crystal clocks are exactly the same frequency you end up getting breaks in the audio due to the beat between the two clocks.
For example, using my Wolfson A/D as the source and my Delta 44 to play back all is well for about a minute - the clocks have then drifted apart enough to cause a frequent ticking sound.
This is not a problem for our project since all the A/D's and D/A's all run off the same master clock.
This was the reason that until the dual sound card Delta 44 we did not have VOX on the SDR1000.
There may be a way round this problem - if you find one be sure to let us know since using the internal PC for playback would be a nice option! 

73's  Phil... VK6APH
]
----- Original Message ----- From: "Edson Pereira" <ewp_jp@ybb.ne.jp> 
To: "Xylo-SDR Discussion" <xylo-sdr@lists.ae5k.us>
Sent: Sunday, January 22, 2006 12:41 PM
Subject: Re: [Xylo-SDR] Saxo



Hi Chris and Phil,

I would like to implement a USB Audio device exactly in order to avoid
having to write any device driver software on the PC side. The USB Audio
Class device specification should not be too complex to implement in the
FX2 (I hope). I have recently acquired the TUSB3200 chip, which is an
embedded USB Audio stream controller. It does however only support USB
full speed (12 Mbps), which will limit the sampling rate to 96 kHz
half-duplex. This is ok for me at the moment since I do intend to use my
laptop internal soundcard for mic and speaker.

I wish the FX2 had an I2S interface!

In my little project, I would like to focus on the implementation of a
96 kHz half-duplex USB soundcard (USB Audio specification)  and a
generic parallel I/O port (USB HID specification). Everything in a
single little board. Anyone on the list interested in joining efforts?

73,

-- Edson

Phil Harman wrote:


Hi Chris,

I have a prototype full duplex USB2 sound card going based on the
Wolfson A/D chip and Xylo/Saxo FPGA board.  At the moment it runs at
48k and 16 bits but the chip can do 192k and 24 bit. Need to walk
first but the pace is picking up!

Writing a generic USB Audio Device driver is way beyond me. Our aim is
to keep the interface to the A/D converter inside the PC as simple as
possible so I don't see the need for a 'real' device driver - we are
not trying to compete with the D44 for example.

73's Phil...VK6APH

Phil....VK6APH



   ----- Original Message -----
   *From:* Christopher T. Day <mailto:CTDay@lbl.gov>
   *To:* xylo-sdr@lists.ae5k.us <mailto:xylo-sdr@lists.ae5k.us>
   *Sent:* Sunday, January 22, 2006 10:29 AM
   *Subject:* [Xylo-SDR] Saxo

   What few useful thoughs I've had so far on the subject agree with
   yours - if possible [does the USB Audio Device spec go as far as
   24-bit stereo, 96/192 ksamples/sec?], the USB-2 interface should
   be able to use a generic USB Audio Device driver => we don't have
   to supply/maintain one for any/all OS. But then, I know almost
   nothing yet,


   Chris - AE6VK


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