HagUSB questions

1UP · « **on:** 13 Oct 2005, 11:18 am »

Hi,

Had a few questions about the HagUSB I hope you can answer:
- is the output "bit-perfect"?
- does it bypass windows k-mixer?
- does it work with foobar2000 and asio?
- is it fine to just not connect the headphone circuitry?
- is it fine to use a 75ohm BNC jack for the spdif?

Cheers!

kfr01 · « **Reply #1 on:** 13 Oct 2005, 03:58 pm »

I would also like to know the answers to these questions.

hagtech · « **Reply #2 on:** 13 Oct 2005, 06:52 pm »

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- is the output "bit-perfect"?

It should be. Unless you use the volume control slider. Software on the PC can easily muck things up with processing. So you need to be aware of the program's operation.

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- does it bypass windows k-mixer?

Don't know. So far I've only tried iTunes and Windows Media Player. There are a gazillion other software choices out there. I am unfamiliar with k-mixer.

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- does it work with foobar2000 and asio?

No idea. Don't have the time, money, or resources to try every possible software application. What I can say, is that the HagUsb becomes the default hardware output audio port for any application. Sort of like selecting a speaker.

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- is it fine to just not connect the headphone circuitry?

Yes. This is also what I do on the CHIME motherboard.

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- is it fine to use a 75ohm BNC jack for the spdif?[/

Yes, if you can make it fit. Not sure there is room in the stock plastic box. The output impedance of the transformer isolated S/PDIF output is set to 75 ohms. Edge rates are very fast.

jh

BradJudy · « **Reply #3 on:** 13 Oct 2005, 07:02 pm »

To help answer some of these questions, I'll say that the answers should be the same as the answers to the same questions about an M-Audio Transit which uses a slightly different chip from the same chip family.

brj · « **Reply #4 on:** 13 Oct 2005, 07:27 pm »

Quote from: hagtech

The output impedance of the transformer isolated S/PDIF output is set to 75 ohms. Edge rates are very fast.

Am I right in my understanding that this means you can use a short cable from the S/PDIF output without having to worry about reflections?

Can you quantify "fast"?

Quote from: BradJudy

To help answer some of these questions, I'll say that the answers should be the same as the answers to the same questions about an M-Audio Transit which uses a slightly different chip from the same chip family.

Are those answers for the M-Audio Transit compiled somewhere?

Thanks for any answers!

BradJudy · « **Reply #5 on:** 13 Oct 2005, 07:57 pm »

The M-Audio Transit spec sheet lists Asio 2 compliance. Various online forums note that it works and is bitperfect, but I haven't tried it myself.

kfr01 · « **Reply #6 on:** 13 Oct 2005, 08:20 pm »

I can try to answer some of the m-audio sonica/transit questions. I use one and find it to be an excellent solution for getting audio out of the computer and to a dac. These answers (rumors?) are based on information gleaned from Empirical Audio

http://www.empiricalaudio.com/frComputer_Audio.html#Product Descriptions

and other forums.

- is the output "bit-perfect"?
yes.

- does it bypass windows k-mixer?
yes.

- does it work with foobar2000 and asio?
yes.

I was just reading over lunch that the easy way to test for bit perfect output, based on what I've read on the forums, is this: try outputing a DTS encoded .wav file from the usb device into a receiver that decodes DTS. If kmixer fuds things up or the output is otherwise not bit perfect, the DTS decoding will not work and you'll get little but static from the receiver. -- Guess I found something to waste my time doing this weekend.

One of these links was here:

http://www.hydrogenaudio.org/forums/lofiversion/index.php/t5755.html

1UP · « **Reply #7 on:** 13 Oct 2005, 09:45 pm »

Excellent, thanks all, looks great.

I'll just peruse the digikey list and put my order in some time over the weekend.

hagtech · « **Reply #8 on:** 14 Oct 2005, 02:12 am »

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Can you quantify "fast"?

Edges are under 5ns, I believe. Really good tranny. Reflections will be determined by the termination, or quality of the connector / receiver in the DAC. With a good 75 ohm cable, you should be able to send this signal dozens of feet. Source impedance (HagUsb) is 75 ohms, so any reflections that do come back are for the most part not re-reflected.

jh

1UP · « **Reply #9 on:** 14 Oct 2005, 08:14 am »

One more question, is it possible to make the unit self-powered, or would this require a new PCB?

kfr01 · « **Reply #10 on:** 14 Oct 2005, 01:30 pm »

If like the Sonica/Transit, then this unit is probably powered entirely by USB.

hagtech · « **Reply #11 on:** 14 Oct 2005, 05:36 pm »

It is presently bus-powered. I figured, why the heck add the expense of an extra floating supply? Made no sense. Add a little filtering, use the onboard linear voltage regulator, does a pretty fine job itself.

You could probably modify unit for self-power. Pin3 needs to go high, maybe some other stuff. See PCM2704 data sheet for details.

jh

HagBMW · « **Reply #12 on:** 20 Oct 2005, 06:25 am »

4 Major Questions:

Why not use the PCM2902 chip? I dont get what is different other than the 2704 is a tad bit cheaper. Does it have to do with inputs (don't need those anyway). I need SPDIF out @ 44khz so my amp can actually read it from a laptop - so no built in SPDIF outputs here. If it is upsampled to 48 (Creative's USB solution - needs external power to boot), no dice - has to be bit perfect @ 44khz. Is the Hagusb the best device out there for my application? (Please don't say yes just to sell me a box

I need to go from 75 ohm SPDIF to 50 Ohm SMB connector. The cable run is going to be no more than a foot. Can I just use 50 ohm cable, and instead of 1 0 0 1 1 0 1 get something like .9 0 0 .9 .9 0 .9, which would be seen as good enough to reproduce loss free audio when the amp does it's D/A conversion? (FYI this is going to take normal 16 bit 128/192 kbit USB mp3 audio into a stock e38/x5 BMW DSP amp.) I assume that it doesnt matter for a short run - it's digital after all but I am no electrical engineer.

I assume if I tried to put 5.1 (or any high fidelity) audio out that the chip cant handle that and it just wouldnt play? Would it make sense to invest in a USB to coax spdif that could handle greater than 16 bits, and could I even get one for under $250? (Not willing to consider a Creative product - it HAS to be 44khz output or the amp will not take it - 48khz will not fit the bill - bit perfect only please).

Is the USB 1.1 a limitation? 12 Mbit/sec should be PLENTY for everything sound related short of uncompressed HDTV audio or raw multi channel dvd quality sound. Given that the chip only handles 16 bits anyway, it would seem like the chip is actually the limiting factor not the usb interface.

Thanks!

kfr01 · « **Reply #13 on:** 20 Oct 2005, 12:45 pm »

The m-audio transit / sonica is bit-perfect.

If your processor decodes DD or DTS the m-audio transit/sonica WILL handle it. (assuming your software is set up correctly).

If the HagUSB solution is similar, it could be the ticket for you.

One thing that confuses me though. You keep saying you want to plug this directly into the amplifier... Does the amplifier have a volume control?

HagBMW · « **Reply #14 on:** 20 Oct 2005, 05:36 pm »

I hope it does... the OBC does have volume control - but I do not know if it will be able to be used without the onboard HU active. I may have to trick it into thinking it is still there.

I can always change the volume via a software controlled volume control, right? Ideally I would want as low a volume level as possible and let the amp do its magic though.

BradJudy · « **Reply #15 on:** 20 Oct 2005, 06:24 pm »

Actually, you don't want to digitally attenuate the volume, that's messing with the signal. You are talking as though your amps have direct digital inputs. Do you have amps with a digital input or are you using a receiver/pre/pro?

hagtech · « **Reply #16 on:** 20 Oct 2005, 06:52 pm »

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Why not use the PCM2902 chip?

Because I didn't need the ADC. At the time, I was just looking for a 44.1k USB input to the CHIME. HAGUSB is just a spinoff product using the same chip.

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has to be bit perfect @ 44khz

Yes, it appears to be.

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Is the Hagusb the best device out there for my application?

I'm sure you can spend a lot more money elsewhere.

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I need to go from 75 ohm SPDIF to 50 Ohm SMB connector.

What really matters is the termination. And cable. I cannot imagine the BMW, or any other amp/DAC, to not use the specified 75 ohm. Find out what the termination is, then use the appropriate cable impedance. If it is indeed 50 ohms, then you can just use an "L" pad on output of HAGUSB for matching. You do lose a little amplitude, but reflections and mismatches are tamed.

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I assume if I tried to put 5.1

Actually, I have no idea. Is it possible for a PC or MAC to play 5.1 discs? My guess is that these would be 96k minimum, which means HAGUSB will not work.

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Is the USB 1.1 a limitation?

No.

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change the volume via a software controlled volume control, right?

You can control volume using the slider/mute control in Windows. But then data is no longer bit perfect.

jh

BradJudy · « **Reply #17 on:** 27 Oct 2005, 01:12 pm »

I have found that the M-Audio Transit does not have the chip I previously believed it to have, so this is not identical to the Transit.