Which DAC?

USB headsets to digital audio workstation software...
Buck
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Which DAC?

Postby Buck » Sat Jul 29, 2017 9:37 pm

I know that when I take audio from the front panel or rear port of my 200D, that I'm using the DAC built into the radio's board. (Incidentally, is there any way to test the accuracy of this DAC, and where is the sample rate set?) If I'm using VAC, I know it uses the DAC of the interface I point Setup towards. For VAC1, this is the UMC202HD into which my mic, phones, and powered speakers are plugged. VAC2, however, points to lines 1 and 2 of Muzychenko's virtual audio cables and then to digital traffic software such as fldigi.

So here's my (other) question. When using M-VAC, is audio being piped directly to the receiving software at the sample rate shown in Setup>VAC2, without any other sampling?

Buck ko0y
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w-u-2-o
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Re: Which DAC?

Postby w-u-2-o » Sun Jul 30, 2017 6:32 pm

Buck,

I'm assuming you are referring to the audio DAC. All of the ANAN series radios, from the 10 to the 8000, use the exact same Texas Instruments CODEC integrated circuit to do this, and to process microphone audio as well. It is the TLV320AIC23B. To see how that chip is utilized, see the schematic for your particular SDR circuit card here.

The sample rate is hard coded in PowerSDR and in the firmware to be 48KHz.

To test the accuracy of the CODEC output you could create a wav file of some sort and play it back through PowerSDR, then measure the results using an audio spectrum analyzer, oscilloscope, or other audio test equipment.

I would suggest that the accuracy of it is not something you need to worry about.

("M-VAC"--Buck, that's a brilliant way to refer to Muzychenko's VAC software, since there are alternatives now. I'm going to use that nomenclature from now on, thanks! :) )

With respect to sample rate conversions, in general nearly all digital mode software uses 48KHz as the standard. However there are some exceptions. You have to study the documentation for the software in question to know if it is different. You can determine what sample rate has been negotiated by looking at the M-VAC control panel after then connection is made.

Note also that it is very important to go into your Windows Sound Control panel and explicitly set all M-VAC cables to operate at 48KHz, both record and playback, to prevent conversions from happening. This is because most software will automatically conform to the sample rate it sees set for the M-VAC cable, thereby preventing any sample rate conversions from being necessary. This is also true if you are using VB-Cable or VMB.

73,

Scott
Buck
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Re: Which DAC?

Postby Buck » Sun Jul 30, 2017 6:45 pm

w-u-2-o wrote:
Note also that it is very important to go into your Windows Sound Control panel and explicitly set all M-VAC cables to operate at 48KHz, both record and playback, to prevent conversions from happening. This is because most software will automatically conform to the sample rate it sees set for the M-VAC cable, thereby preventing any sample rate conversions from being necessary. This is also true if you are using VB-Cable or VMB.

73,

Scott


I concur, and would even add that Sound Control Panel on all devices should be re-checked periodically. I've seen Windows change those settings with no warning or apparent reason. I've also set the M-VAC cables in their control panel to use only 48K. Thanks for the other info.
K9RX
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Re: Which DAC?

Postby K9RX » Mon Jul 31, 2017 12:06 am

Jumping on this discussion if I may.... I watched G7CNL (?) video on setting up M-VAC (i had up until now referred to it as VAC (Eugene) but prefer this as well) ... he says to set the sampling to 8K to 192K ... which of course I did. I have the sampling for this set to 48K on the radio (PSDR) ... but when I launch M-VAC's CP it shows that the cables are coming up as 192000 and not 48K! I have checked Windows Sound panel - it had them as 48K but only 16 bit - I since changed them to 32 bit ... I assume its just oversampling ... but is this potentially an issue with latency or whatever? Yesterday I noticed I was getting these annoying clicks in the audio ... first time I'd heard them (and once again not there today).

Gary
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Buck
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Re: Which DAC?

Postby Buck » Mon Jul 31, 2017 12:44 am

Gary, if you set 48K to 48K on the M-VAC control panel for both cables it won't let any client program set another rate. It may give an error if any tries it, I don't know about that. I think, though Scott may correct me on this, that the clicking is more likely a function of buffer and latency settings.

Buck ko0y
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w-u-2-o
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Re: Which DAC?

Postby w-u-2-o » Mon Jul 31, 2017 1:04 am

Yes, Buck is correct. :)
K9RX
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Re: Which DAC?

Postby K9RX » Mon Jul 31, 2017 3:36 pm

ok .... but I'm not sure you addressed my question - or if you did I didn't get it .... again PSDR is set to 48K. WSJT is looking for 48K ... when I "use" this setup and I open up M-VAC/CP it shows ...Ok - I just looked at it today:
Cable 1 line in to WSJT shows: ExtPCM/192000/32/2(3)
Cable 2 line out from WSJT shows: EXTPCM/48000/32/1(1) (this had been showing as 192000!)

If this is fine then I'm fine ... Simon (G7CNL?) had shown in his video that these values both end up as 48000 ... that is the only reason why I'm asking.

Gary
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w-u-2-o
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Re: Which DAC?

Postby w-u-2-o » Mon Jul 31, 2017 4:13 pm

I don't currently use M-VAC so I can't easily check this. However it does not make sense. If M-VAC recording and playback devices (cables) are set to 48KHz in the Windows Sound Control panel advanced settings tabs, it should all be shown as 48KHz in the M-VAC control panel. So I do not have an easy answer for you. However, in the past, when I did use M-VAC, all active connections always showed up as 48KHz for me.

You can, as Buck says, set the constraints on your M-VAC cables such that they only run at 48KHz. It's not a bad way to ensure that this occurs.

Of course, all of this weirdness with M-VAC is why I use Voicemeeter Banana now instead ;)

If you are interested in Voicemeeter Banana (VMB), you might take a look at my tutorial here.

73,

Scott

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