Flex 6000 Digital Audio Encoding

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I'm looking at the SmartSDR Software Users Guide in the DAX section (starting on page 112) and I'm trying to understand what format the digital audio output in a DAX channel is?  I see that it is digitized audio but is it PCM or DSD encoded or something else?  This is probably quite obviously documented somewhere but I must be missing it.
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Richard McClelland, AA5S

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Posted 2 years ago

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Richard McClelland, AA5S

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I think that I saw the dax audio is in a 44.1kbps digital channel.  I'm not seriously into audio but I think this implies PCM encoding.

Along the same lines, in the Hardware Reference Manual, page 30:

"7.23 OUTPUTS [1, 2, 3]
Open drain digital outputs. Possible future product feature - not currently enabled."

Maybe Flex is planning to put the audio from the active slice to one of these outputs as DSD single rate (2.8MHz) or double rate (5.6MHz) raw.  This would be handy in order to route the audio directly to a DAC (e.g. http://www.psaudio.com/nuwave-dsd/) so that the audio wouldn't have to pass through a client computer at all.  Might also be possible to grab the audio from pins 12/15 of the ACC connector?
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Richard McClelland, AA5S

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So, to continue my rhetorical conversation, 44.1 kbps PCM audio available on an external connector should be more than sufficient for communications.  The audio purists amongst us might want to utilize 5.6 Mhz DSD so that they can post-process the audio to make it sound like they they are in the fourth row of the Temppeliaukio Kirkko as they listen to code emanating from the pulpit
(Edited)
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Ria - N2RJ, Elmer

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It's PCM and the sample rates I get from Windows are as follows

Since all it is is a virtual driver they could probably output any of those sample rates and bit depths without issue. 
(Edited)
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Richard McClelland, AA5S

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Thank you.  Do you see a way to get this PCM bit stream directly from the Flex 6000 rather than via DAX?  Not a high priority for me since I don't own a Flex 6xxx but I became curious after I saw a DAC vendor's claim that they could process any digital audio bit stream.  Seems like a circuitous path to go from the Flex to the computer to DAX then out via USB to a DAC. 
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Ria - N2RJ, Elmer

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The only way without a client computer right now is via ethernet API but you'll still need some sort of client device to stream audio from the radio. They do have a possible future product feature as you may have noticed on pins 26, 27 and 28 but that has not been enabled in any publicly available version of SmartSDR. 
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Richard McClelland, AA5S

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Well, now we have a reason to activate one of those ports!  There is probably 1ms less delay going directly from Flex to DAC without passing through the computer on the way.
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Eric - KE5DTO, Official Rep

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The audio coming over the wire from the radio for DAX is floating point at 24kHz wrapped in a VITA-49 style packet.

Once the DAX application gets a hold of the data, it converts this into a typical Windows Sound device, so it can be used a various rates and formats by other sound card based applications.  This is primarily for legacy applications that require a sound card interface.  Clearly it would be less latency (and less chance for resampling issues, etc) to eliminate the sound card part and go straight into an application.

As Ria said, there is nothing preventing someone from using the Ethernet API to access the same kind of data streams.  It will require some sort of application on the other end to accept the bits and do something useful with them.
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Richard McClelland, AA5S

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Thank you for chiming in, Eric.  As usual, things are more complicated that I had imagined.  Here is the vendor's comment that got me interested in the first place: "DirectStream converts all digital inputs, including PCM, to pure 1-bit DSD, in an elegantly-simple path."  When I saw that, I thought to myself that I could probably choke their device with a Flex and that looks to be true.  :-)
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Eric - KE5DTO, Official Rep

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So PCM is typically raw integers with no headers, etc.  You could get to that pretty easily from what we have, but it's a little different.  I've never heard of DirectStream.  I'll have to look that up.
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Richard McClelland, AA5S

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Accommodating this particular DAC probably won't become an issue for Flex anytime soon since this thing costs almost as much as a 6700.
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Richard McClelland, AA5S

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On the other hand, Flex should hire their engineer because this guy is so eccentric that Flex could make a video like this and charge $16k for the next Flex:  https://www.youtube.com/watch?v=mRg-Rrd2blY.  Pristine clocks are essential for the discerning Amateur, after all.
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Ken - NM9P, Elmer

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Eric, if I remember previous conversations correctly, since you are using 24KHz sampling, it relatively easily can be scaled up or down to 8, 12, 48, etc. for use in other "sound card type" Digi software without all the conversion remainder errors, etc.?  Using the 44.1 KHz CD standard would be more problematic.
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Ken - NM9P, Elmer

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Eric, if I remember previous conversations correctly, since you are using 24KHz sampling, it relatively easily can be scaled up or down to 8, 12, 48, etc. for use in other "sound card type" Digi software without all the conversion remainder errors, etc.?  Using the 44.1 KHz CD standard would be more problematic.
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Sergey, R5AU

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Ken no sense how you are scaling in any way this is re-sampling with appropriate effects. You can try it ex. with Fldigi