Has anyone tried a CX31993 USB DAC with FreeBSD?

Zare said:
Not an Apple developer so this might be stupid question, but iPad apps cannot generically access USB, only through class-compliant abstraction?
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Yes. The specific issue is that Apple doesn't allow you to load drivers on iOS/iPadOS/TvOS.

This could be used as a good marketing gizmo for FreeBSD audio peripherals. "If it works on iPad, it works for us".
Click to expand...

That is the case. But you can't rule out that there are devices which were made to work on iOS by try-n-error and aren't quite clicking with FreeBSD. Never seen one, though.
 
I would say specific issue would be lack of libusb since it looks like it could've ran on jailbroken devices at least 5 years ago judging by posts.

So yeah the general issue is Apple doesn't allow drivers, kernel or userland of this type which forces apps to use class compliant access to USB audio hardware. Now there may be tricks possible especially through umidi and sysex messages that hardware and iPad app understand, and our ecosystem doesn't.

I don't think this is a problem tho, that communication is plain and can be sniffed and reproduced, if the device really needs to be initialized by proprietary protocol running over the wire in standard format.

Therefore I will be using this 'iPad compatibility' in advocating FreeBSD audio for sure :)

cracauer@ said:
Sound Devices' MixPre 1 is such an example that is registering as class compliant but useless since by default nothing is routed.
Click to expand...

Could 'replay attack' be used to initiate the device maybe?
 
Zare said:
Could 'replay attack' be used to initiate the device maybe?
Click to expand...

Yes, I had the same thought. I have a full USB trace of WIndows XP initializing the MixPre 1 (they never even released software for 64 bit Windows).

But it had too much hair for a quick hack to make it work. For starters it seemed to have a complicated handshake to download a firmware blob.
 
Yeah such things can get elaborate. I guess if there is a will there is a way, and that could start happening for any contemporary devices if FreeBSD audio starts gaining users on grounds of its merit. Also having any kind of Linux code for said device could help - even inside a proprietary application.
 
It's kind of a shame that setting hw.snd.default_auto to 1 didn't appear to work for me. It's supposed to assign hw.snd.default_unit to the most recently plugged in device, but it didn't seem to do anything, and I had to assign it manually each time I plugged one in. Is that any kind of known issue? it's only a small thing but it would be nice if it was automatic.
 
For USB sound devices I use a small script that sets up all sysctls and the default device and gets called by devd.

E.g.:
/usr/local/etc/devd/smsl.conf
Code: 
notify 100 {
    match "system"        "USB";
    match "subsystem"    "INTERFACE";
    match "type"        "ATTACH";

    match "vendor"        "0x152a";
    match "product"        "0x85dd";

    action "/usr/local/etc/devd/smsl_setsysctls.sh";
};

notify 100 {
    match "system"        "USB";
    match "subsystem"    "INTERFACE";
    match "type"        "DETACH";

    match "vendor"        "0x152a";
    match "product"        "0x85dd";

    action "/usr/local/etc/devd/defaultpcm.sh";
};
/usr/local/etc/devd/smsl_setsysctls.sh
Code: 
#!/bin/sh

uaudionum=`sysctl dev.uaudio | grep "SMSL USB AUDIO" | cut -d'.' -f3`

pcmnum=`sysctl dev.pcm | grep uaudio$uaudionum | cut -d'.' -f3`

#sysctl dev.pcm.$pcmnum.play.vchanformat=s32le:2.0
#sysctl dev.pcm.$pcmnum.play.vchanrate=192000
sysctl dev.pcm.$pcmnum.play.vchanmode=adaptive
# bitperfect requires vchans to be disabled to work properly
sysctl dev.pcm.$pcmnum.play.vchans=0
sysctl dev.pcm.$pcmnum.bitperfect=1

hw.snd.feeder_rate_quality=4

mixer -d $pcmnum
mixer -f /dev/mixer$pcmnum vol=1 pcm=0.9

sysctl hw.snd.default_unit=$pcmnum

the 'defaultpcm.sh' simply sets hw.snd.default_unit to the onboard sound just to get everything back to a 'known state'. I don't use the onboard device at all, and the USB DAC/AMP is always connected, so I could as well just omit the DETACH rule.
 
I've just been trying out the JM20 on a T490 thinkpad. It sounds much better than the T490's motherboard DAC, which is a realtek ALC257. In fact the X201/X220 conexant chip sounds quite a lot better than the T490 mobo chip too, which is kind of surprising. Anyway the JM20 is a good upgrade for the T490, especially at the price I paid.

Just going by the particular chip might not be the whole story either, the circuit implementation that has been used also matters. The classic example was the NAD3020 which used bog-standard 2N3055 power transistors yet got real hifi performance out of them. The realtek chip.in my mini pc sounds excellent, for example. All you can really do is listen to devices and find one you like.
 
I finally found out that the secret to getting auto configuration of a usb dac when you plug it in and pull it out is to set hw.snd.default_auto=2. It is actually documented in the "sound" manpage. If you set this in /etc/sysctl.conf, you no longer need to manually assign the default_unit after plugging a usb dac in. it works very well. This doesn't set bitperfect up though, for that you need sko's devd script posted above.
 
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I've been trying various headphones with the JM20. Sennheiser HD560S work really well with this cheap usb dac, imho. Sounds really good with mpd+thinkpad+freebsd 14.4, and that's just with 41k/16bit audio, and not bothering with bitperfect. Nice budget system. Fantastic sound quality for the money you've paid... if I think back to what hifi kit used to cost. I recommend this combo.

Hint - audio/mixertui is a nice front end to freebsd's oss mixer; hardwire pcm to 100% and then vary volume with master. Or for windowmaker people, you can use wmix.

www.audiosciencereview.com

JCALLY JM20 Headphone Dongle Review

This is a review and detailed measurements of the JCALLY JM20 USB-C headphone adapter (DAC and Amp). It is on kind loan from a member and is on sale for US $24. Not much to say about the construction so let's get into measurements. Speaking of that, I finally have a fix for this class of...
www.audiosciencereview.com www.audiosciencereview.com

www.sennheiser-hearing.com

HD 560S

The HD 560S indulges the audiophile evaluating their music’s entire journey through the audio path. This open-back headphone is tuned to reveal the truth in your music without sacrificing the gratifying bass response needed to reproduce complex modern music—all at a breakthrough value. Its...
www.sennheiser-hearing.com www.sennheiser-hearing.com

Yes, your $4000 Focal's probably do sound better, but this isn't bad for the money. There is actually some genuine bass extension, without sounding woolly or booming, which is always difficult to achieve in headphones. Would probably be better with an offboard headphone amp/psu, but I can't be bothered with all the cabling on a laptop. And this is highly portable.

BTW... I haven't heard any problems with clicks, pops, fade, etc that other people mentioned. It works really well.
BTW.2 I should probably have added... I'm just using pure oss. No pulse, pipe, jack, or anything else.
 
One more useful tip on the JM20, about how to use the output amplifier headphone impedance matching, gleaned from the discussion after the ASR review.

Quote:-

"If you plug in your headphones before you power up the JM20, then the dongle will measure the headphone impedance on startup and limit output voltage accordingly:
This effectively prevents clipping and is what JCally base their output power specs on (0.95Vrms @32Ω =28mW per channel, same as the US Apple dongle).

You can bypass this impedance sense auto gain mechanism (which Amir likely did by accident) by powering up the JM20 with a high impedance load or an open headphone plug (e.g. headphone adapter), then connecting your actual headphone load.

That way, you can get about twice the output power or +25% perceived volume at 32Ω."

I find there is plenty enough power to drive the H560S if you plug the headphones into the JM20 before plugging the JM20 into the computer, in other words, when the impedance matching is in operation, which gives the best performance without clipping; especially after setting the pcm volume level to 100% with 'mixer' or 'mixertui'.
 
There is a spec sheet on the JM20 series usb dacs here. https://manuals.plus/ae/1005002272265385

I have ordered a JM20 MAX to try, out of curiosity. It uses the same CS43131 dac chip as the JM20, but adds a dual audio opamp output buffer for more drive power, and can support higher impedance headphones up to 600 ohms, Interestingly the output buffer is from the beijing company sgmicro, there is a data sheet here: https://www.sg-micro.com/rect/assets/e637497c-405d-45a6-88dd-21c16c22188f/SGM8262-2.pdf
 
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