Fw: [softrock40] Re: USB Soundcard (minimal size)

Terry Fox wb4jfi at knology.net
Mon Apr 2 14:45:43 CDT 2007

Frank & Tacos:
Here is a possible fix for audio issues with softrock demos and laptops.  The board is cheap $25 kit, $35 built.  I have ordered one for me and one for Mel to play with.  It will NOT be the best in the world, but should be adequate for demos and simple operations.

Another next step would be to build the same kind of device, but with a better sound chip.  That would require a better computer interface than the simple USB devices that are easily obtained.  It appears that both Windows and Linux have generic USB-sound device drivers that some of these chips can take advantage of.  I'm not sure that same generic driver interface is available for firewire, if it is, I would go firewire.  The Firewire interface is designed to be faster, and more reliable, which would be good for SDR applications.

I wonder if we could get to the point of doing sound-card testing.  Having some absolute measurements would go a long way top say what is and is not acceptable performance with SoftRocks.

The other way to go is full-band sampling, then downconverting or downsampling, like the SDR-14 or SDR-IQ.  The problem with this scenario has always been dynamic range of the A/D converter.  It appears you really need at least 24 (or more) bits to achieve the dynamic range for good HF performance.  Some present designs use switched preamps and/or attenuators to maks up for only 12-16 bits of A/D.  That works OK as long as the signal of interest is still there when "adjusting" the front end sensitivity.  But, if putting in 16db of attentuation to prevent A/D overload also puts the signal of interest into the noise, you have still lost.

Anyway, this is another possible tool.

----- Original Message ----- 
From: Edson Pereira 
To: softrock40 at yahoogroups.com 
Sent: Monday, April 02, 2007 7:22 AM
Subject: [softrock40] Re: USB Soundcard (minimal size)


The PCM2900 will give you a quite usable sound card when compared to
most internal cards. It will not compete at all with a Delta-44 and it
will limit a bit the dynamic range of a QSD (to around 80 dB), but it
will work well in most casual operating conditions. Actually, it will
perform rather well when you get used to it since it is so simple to
use. It has only *one* adjust: Audio Out. I learned to appreciate that
and can have the QSD gain adjusted to match the 2Vpp ADC input limit.

TI has a big brother chip, the TSUB3200. This chip is used in many
audio interfaces, but it requires firmware development (8052) and is
still limited to 48 kHz sampling rate (it is possible to do 96 kHz,
but only in half-duplex).

We are in desperate need for a simple audio interface with 96 kHz
24-bits sampling rate and a good CODEC. The former Xylo project had
that goal, but it grew into a huge multi-faced project.


-- Edson, pu1jte, n1vtn 

--- In softrock40 at yahoogroups.com, "Terry" <wb4jfi at ...> wrote:
> Yes, it is pretty lame compared to a good firewire card. But, when 
> faced with a laptop that only has mono-mic inputs, this looks better 
> and better.
> For laptops, I have the Audigy 2 ZS PCMCIA card, which works OK under 
> Windows. And, I have an Exitgy USB card that works under Linux 
> (windows is half-dux only due to the 1GHz laptop). The Extigy card 
> is as big as the laptop, and requires external power. The Audigy 2 
> won't work under Linux, and is PCMCIA, which is going away in newer 
> laptops. I also have a Delta-44, Fiji PCI, Montego PCI, Santa Cruz 
> PCI, Audigy 2 PCI, Audigy 4 PCI, and a Sony firewire audio converter 
> for desktop operations.
> There are few good, inexpensive laptop alternatives. Yes, I can buy 
> an expensive USB or Firewire card, but is a $400 sound card really an 
> acceptable "peripheral" to a $13 SoftRock lite or $32 RxTx? I don't 
> think so. If I'm spending that much, I'll buy a rice-box rig. Wait 
> a minute, I did, and the FT-817 works great.
> What I want is NOT the end-all, be-all sound card that will blow away 
> an Orion. I want to demo, and possibly use the SoftRocks with a 
> laptop on occasion. Either traveling, or just for fun. That is 
> where this interface may come in. With only 93db SNR and 48kHz 
> sampling, I don't expect to hear the world. But, I will bet that it 
> works as good as, or better than the AC97 desktop PC moboard sound 
> cards. And it is small and portable. Just right for my laptop 
> needs, if it works out.
> I don't think it will cripple a SoftRock at all, I think it may do 
> the opposite, enable more SoftRocks to work with laptop computers in 
> an inexpensive yet usable setup. That is a top complaint I see here 
> on the forum - SoftRocks with laptops. (another for me is a DDS LO)
> Thanks for the comments, and allowing me to state my case.
> Best 73s.
> Terry
> --- In softrock40 at yahoogroups.com, "RAY" <WA2HVI@> wrote:
> >
> > IMHO: I just came from the spec sheet and from all appearance this 
> chip will 
> > cripple a softrock receiver in a few ways - yes it is minimal and a 
> lot I/C 
> > for the buck for its size but also minimal in performance. 
> Perhaps I 
> > missed something on the spec sheet - I would love to be wrong. It 
> is a nice 
> > stereo chip.
> > 
> > 73, Ray, N0FY
> > 
> > 
> > ----- Original Message ----- 
> > From: Terry
> > To: softrock40 at yahoogroups.com
> > Sent: Sunday, April 01, 2007 7:32 PM
> > Subject: [softrock40] Re: USB Soundcard (minimal size)
> > 
> > 
> > Thanks Ignacio, I just ordered two built units to play with. Any
> > idea on Linux support?
> > Terry
> > 
> > --- In softrock40 at yahoogroups.com, Ignacio Cembreros <eb4apl@>
> > wrote:
> > >
> > > Terry wrote:
> > > >
> > > > Hello Tom,
> > > > Have you played with the PCM2900 to see how well it works with
> > > > SoftRocks? Are there appropriate drivers for Windows XP and/or
> > Linux?
> > > >
> > > >
> > > > I ran into a reference to an article in Nuts and Volts from June
> > 2005
> > > > that has a board available for $25-35 that incorporates this 
> chip,
> > > > and was wondering it this setup would be good for laptop 
> softrock
> > > > use. I presently use either the Audigy 2 ZS PCMCIA, or an 
> Extigy.
> > >
> >

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