Benchmark DAC1 now available with USB

[thomaspf]

That sounds about right. A shorter way of saying this is that an ASRC is not removing jitter but translating it into very low level broadband noise.

[Crowbar]

But ASRC allows the filtering of jitter.

Of course, if you recover a clock by high quality PLL you still filter it.

[chiamingen]

I just got my dac1 yesterday. It sound great like everyone had said
I notice there are no way to switch off the dac, only the standby mode.
So whenever i wanted to switch it if i just plugged out the power socket. Is that the right way to switch it off? Will it damage my dac in long run?

[Wavelength]

Originally Posted by ted betley

Ok Elias I have a problem with pops/crackles. I'm using dell xp sp2 cicsplayer -> asio 4all-> opticsis cable-> generic usb cable-> benchmark dac and the sound is fabulous. However I get these pesky pops every now and then (it went away for 3 days after I plugged my mouse/keyboard usbs into the front of the dell leaving my audio usb output all alone except for non used periferalls). I set my latency high in asio4all. Don't know what else to try. Any ideas?

Ted,

A couple of things come to mind. First on your dell all the USB ports are not created equally. Depending on which one you have that could be the whole problem. If you have a desktop machine NEVER use one of the front USB ports. If you are using a laptop and one from the same side as the DVD drive then go to the other side. Also many times there are internal hubs and you could be sharing with other devices. There is a crude program called USBView you can google it and find what the tree looks like on your computer or go into Control Panels and look at the device tree and make sure you are directly connected to one of the HOST ports.

The other problem is in the Opticis power supply. That thing is like $1.73 power supply and reaks havoc on anything attached to it. What I tell customers is buy a linear 5v regulated (must be regulated). Hack off the 1.7mm cable from the opticis supply and hack off the (usually 2.5mm) connector on the 5V supply and wind them together to get a better supply.

Guys... Dell computers are cheap for a reason. Don't spend a large chunk of change on the dac end and expect the cheap Dell to do it's job.

You may also want to make sure you have the latest USB drivers. These are available from the company who makes the chips. Primarily Intel, look up the chip type in the Control Panel Devices and then go to the companies website and download the latest drivers.

Also make sure at the end of the opticis cable that you are using a good USB 2.0 cable. Believe me it will make a difference.

Thanks
Gordon

[ted betley]

thanks gordon. I am using a backside usb port and a battery power supply for the opticsis. I just got rid of all the anti virus stuff. We'll see how that works.

[Wavelength]

Originally Posted by Crowbar

But ASRC allows the filtering of jitter.

Of course, if you recover a clock by high quality PLL you still filter it.

Crowbar,

With a PLL it is true you are filtering the input control voltage to the VCXO, but the PLL output is not necessarily filtering the jitter like an ARSC would. The PLL output is usually based on some relative input clock. For SPDIF that is usually the Frame Sync. The output PLL of the SPDIF therefore gives you MCLK which is then divided down to Bit Clock and Word Clock.

In Adapative mode USB the reference becomes the SOF frame which comes at what every the rate of the enumeration is applied (typically 1ms).

With an ARSC the data is pumped in serially to a parallel register array. The math is done then pumped out using a completely different clock.

In the past it was thought that only jitter on the Frame Sync (or SOF for Adaptive USB) caused jitter in the system. While true this is where a large precentage of the jitter. But now there is evidence that jitter can develop in many areas of the Digital Audio system. It can be between the DATA and Bit Clock, between Word Clock and Bit Clock.

There are many ways to filter this. Some designers re-clock the Bit Clock, Word Clock and Data right before the DAC. Sometimes a secondary PLL/VCXO is used to re-clock thereby reducing the clock jitter. Others use secondary PLL/VCXO and use fifo's to buffer the Word Clock and Data into the DAC which has similar results to an ARSC.

Again Crowbar as you mentioned the ARSC and the fifo method both have the problem of jitter into their systems, some of which cannot be removed.

It's been kind of interesting to follow some of the Stereophile tests of USB dacs that also support SPDIF and utilize ARSC's. If what most of the designers say were true then the jitter specs for all inputs would be the same. But as we see that is not really the case. Albeit there have been some errors in measurement done there. But still it is very interesting to look at the results.

Thanks
Gordon

[Wavelength]

Originally Posted by ted betley

thanks gordon. I am using a backside usb port and a battery power supply for the opticsis. I just got rid of all the anti virus stuff. We'll see how that works.

Ted,

Dave Clark of Positive Feedback could not get his Dell to work. It always had the same problem you are plagued with. I don't recall what dac he was using but he finnally went to another computer and all's fine.

Yea part of the problem here is there is little emphasis on quality parts these days.

You may still want to find a copy of USBView and make sure nothing else is sharing that port (like bluetooth).

Thanks
Gordon

[poo]

Originally Posted by chiamingen

I just got my dac1 yesterday. It sound great like everyone had said
I notice there are no way to switch off the dac, only the standby mode.
So whenever i wanted to switch it if i just plugged out the power socket. Is that the right way to switch it off? Will it damage my dac in long run?

Listening to mine now... smooth hey!

It's designed to be left plugged in, and will go in to standby (as you know) when not in use. No need to turn it off or unplug it (though Greenpeace may suggest otherwise...)

[ted betley]

Gordon if I have to I will buy another computer. What did Dave buy to fix his problem? What do you recommend?

[EliasGwinn]

Originally Posted by ted betley

when is a good time to call

I'm here Mon-Thur, 9a-5p EST. Rory (our sales person) is here M-F, 9-5.

1-800-BNCHMRK (800-262-4675).

We'll get this figured out or we'll fix it for you.

Thanks,
Elias