Computer interface measurement help required

[ddaudio]

I'd suspect that Audacity is (needlessly) applying dither. It shouldn't be doing that when recording in 16 bit and exporting as such but you never know... change quality settings and you should find out in short order. I think I've previously run across an issue like that in older versions.

BTW, Intel Atom suggests netbook-grade hardware so I presume that's 2 GiB worth of memory and not just 2 megs (which would be more befitting of a 286 or 386). In which case it would be more well-appointed than the machine I used to make lots and lots of radio recordings using Audacity 2.0.6 15-20 years ago.

On another note, it seems you can only record straight to 44.1 with the MDS-JE510... here's to hoping that the ADC anti-alias filter is sufficiently bombproof, not to mention anything about its passband ripple (a measurement of frequency response would be interesting, noting that you're looking for variations sub-+/-0.1 dB). Odds are it's a fair bit better than the Aztech ISA card (probably with a CS4248 codec) that I did my first vinyl rips with way back when, but possibly not quite as good as the WM8770-based jobs I relied on for years (although that one didn't exactly have good filter ultimate rejection at 65 dB, so oversampling would be recommended).

It would appear that measurements for the ADC sections of MD decks are a bit hard to come by. We roughly know what to expect in terms of dynamic range (probably low-mid 90s dB(A)), and distortion should be low enough either way, but nobody ever tests filter ripple and out-of-band rejection.

Thanks for the info. I'll have a trawl through Audacity settings. It's v2.4.2 on the Foxconn device.

Yes, of course, 2 GiB of memory! I could cut down on resource usage by using a local screen rather than using ssh or xrdp from my armchair. And maybe by installing a very lightweight window manager. When I first set it up, I was working with an ethernet cable plugged in to my router, and Audacity was usable for capture, but after transferring to another room, I'm reliant on the ancient wifi card.

It would be nice to get Audacity working better, if only to be able to insert track breaks in real time. But when it comes to checking for clipping, normalizing, etc it's much better to transfer the project to my i5 laptop first.

As I said before, I'm sure the quality is already more than enough for digitizing old secondhand vinyl - the cleaning is the real challenge. But this ADC stuff is interesting in its own right. I could also try an old HK AV receiver I have to do the ADC: unlike some it will digitize its analog inputs for coax output (I'm not sure what sampling frequency it uses). And just for fun, even my WiiM Mini, with its known quite bad ADC. Would be an interesting comparison with the Sony MD.

Then I could try using my Cambridge 840C to upsample the digital output of all three before feeding into the computer. I might start another thread with a proper comparison. I could call it "ADC from my hifi graveyard"

Would an REW-generated sweep file be good for testing the frequency response?

 

[xanalog]

Would adding an E1DA Cosmos ADCiso into your audio toolbox help?

 

[DVDdoug]

Thanks for the info. I'll have a trawl through Audacity settings.

Dither is under Edit -> Preferences -> Quality and you can set them both to "None".

It really doesn't matter but...
Dither is added noise that's supposed to sound better than quantization noise.

The "rule" is to dither when you down-sample. If you are recording at 16-bits and exporting at 16-bits you shouldn't dither. Audacity works internally at 32-bit floating-point and I don't think it knows what bit depth you recorded at or what you imported so it doesn't know if you are down-sampling or not.

You can't hear quantization noise or dither at 16-bits under any normal listening conditions so you can't normally hear dither (or the lack of dither). It's one of the least important things. (You CAN hear quantization noise at 8-bits.)

With vinyl (or almost any analog source) the analog noise is a lot "worse" than dither noise, so there's no need to add more noise. But if you do add dither it's so low that you'll never hear it mixed-in with the original noise. With the incoming analog noise, it can also be considered "self dithered", but of course no analog noise would be better.

 

[ddaudio]

Dither is under Edit -> Preferences -> Quality and you can set them both to "None".

Thanks, yes, that got rid of the noise above 13k and produced effectively identical results to SoX on the command line.