[Linrad] Re: Duplex

[Pierre Vanhoucke <skynet.be; pierre.vanhoucke@xxxxxxxxxxxxxxxx>]

Hi Leif,

The hardware differences between the SB16 and the AC97 chips can be
found at
http://www.sparkysworld.co.uk/soundcards.htm
 
Pierre / ON5GN

 at On Mon, 2008-07-21 at 17:12 +0200, Leif Asbrink wrote:
> Hi All,
> 
> For Linrad to work as a transceiver with 96 kHz I/Q as input
> and output for the RF signal, a Delta44 soundcard works fine.
> Two more audio channels are needed however, one for loudspeaker
> output and another for microphone input. (The loudspeaker has 
> to be stereo for full receive performance.) 
> 
> Good old ISA soundcards like the Soundblaster 16 would fit nicely,
> but modern computers do not have any ISA slot. The AC97 or INTEL ICH5 
> which is built into my motherboard would have been fine if it
> had been possible to disconnect the input from the output.
> I have tried both 4Front and ALSA but none of them has a mixer
> software (that I can find) that allows me to prevent the loudspeaker
> signal that Linrad sends to the card to appear on the microphone
> input line. The good old soundblaster had llinesw and rlinesw for this
> purpose in ossmix.
> 
> The AC97 mixer has a myriad different controls but none of them affects
> the presence of the output on the input stream.
> 
> What have I missed? I find it hard to believe that the architects
> behind a complicated system like the AC97 did not think about this.
> Maybe the authors of ossmix/alsamixer just did not provide access
> to the appropriate control register?
> 
> Is there anyone who knows? As things stand now, I have to use three
> different soundcards to make the Linrad transceiver operational.
> Utterly stupid! I need the third card in another computer.....
> 
> Few of my soundcards are useful for the transceiver mode since only
> those for which I can set a small DMA buffer give a decent timing.
> I need less than about 50 ms from key-down to loudspeaker output
> (10 ms key to antenna and 40 ms from antenna to loudspeaker.)
> Having buffers that delay by 0.1 second both at the loudspeaker
> output and at the microphone input really hurts. Setting a ridiculously
> high sampling speed solves the problem partly, but being able to 
> run the AC97 in full (independent) duplex would be far more satisfying
> (although it uses a ridiculously high sampling rate internally.)
> 
> 73
> 
> Leif / SM5BSZ
> 
> 
> > 


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