[jp11801]

Quote:

Originally Posted by Soundproof /img/forum/go_quote.gif Hi Gordon, You're touching on something that had me quite pleased, once I realized it. The CDP is just a way of getting the information off the disk and on towards the amplifier and speakers. Placing that same information on a high-quality, fast harddisk - and having it read through a computer's more sophisticated setup of error correction and buffers has to be superior. The challenge is then to ensure that the data goes uncompromised out of the storage device/computer and to the DAC. Which Firewire or USB methods would you recommend out of a Mac? I have been using TosLink and USB.

I have the same questions, I use an Imac and can use either an optical cable or firewire out of it to my apogee minidac. Maybe it's the mental illusion of the $$ optical cable but I would swear the optical sounds better. The weird thing is the optical cable from what I understand should not sound as good due to jitter induced by the conversion process?

 

[bbrandt]

Quote:

Originally Posted by Soundproof /img/forum/go_quote.gif ... Which Firewire or USB methods would you recommend out of a Mac? I have been using TosLink and USB.

This would depend on the USB implementation on your USB/DAC device. S/PDIF implementations on PCs are uniformly cheap, and a Mac is probably no exception. Since it is a synchronous protocol, this setup can be prone to "jitter". USB can theoretically be fully asynchonous and buffered, eliminating jitter before the DAC, but I have not seen a fully async USB implementation yet.

Since you will have the option of both with your Mac, your ears will be the best judge.

 

[musicmind]

Does anyone have some information on the use of firewire vs USB for audio in such a computer setup?
While many comment that USB is not suited for audio, because of its "burst transmission" nature, I dont see much talk/implementation of firewire interface, which seems to me would be immune from a few such issues. Is the lack of support for firewire to do with some unsuitability of firewire itself, or because firewire is not as well known in the PC world compared to firewire and therefore not economicially feasable to impletment?

If anyone has found any decent articles and information, it would be much appreciated.

Many thanks.

 

[bbrandt]

Quote:

Originally Posted by Wavelength /img/forum/go_quote.gif ... Another problem as I indicated is that depending on software, drivers, hardware etc... a computer can sound different. I have a USB analyzer and you would be surprised at how some ports respond. ...

(moved original post to correct forum)

It is possible to get "bit perfect" output across the USB transport (i.e. the PCM bits in the USB frames are identical to the PCM bits in the source audio file on disk). The main challenge is getting the software stack not to mess with the audio.

 

[audioengr]

Quote:

Originally Posted by bbrandt /img/forum/go_quote.gif 2. The Windows mixer, while good for general use, is not the way to get bit-accurate transport...

Used to be true, but with the new "driverless" firmware licensed by Benchmark Media and Empirical Audio, the output is truly bit-perfect, from XP, Vista and MAC.

Steve N.
Empirical Audio

 

[DrBenway]

Quote:

Originally Posted by audioengr /img/forum/go_quote.gif Used to be true, but with the new "driverless" firmware licensed by Benchmark Media and Empirical Audio, the output is truly bit-perfect, from XP, Vista and MAC. Steve N. Empirical Audio

Any way I can make a desktop running XP do this...?

 

[Soundproof]

I'm presently using Airport Express to port music to my Grace m902 DAC/Headphone amp.

A TosLink cable goes from the Airport Express to the DAC. Very convenient when I want to do playback from my Laptop.
Is it bit transparent?

According to Stereophile magazine it is. And the comment about this only being valid for iTunes is no longer correct. I use Airflow to hijack other media sources, including VLC, and then play back through the AE.

http://stereophile.com/digitalprocessors/505apple/

Though the AirPort Express includes a lot of computer functionality for $129, I'll refer you to the computer magazines and the Web for that information. For sound, the AE outputs analog audio on a 3.5mm stereo minijack. At first glance, it doesn't appear to have a digital output, but at the innermost end of the 3.5mm jack is an optical S/PDIF transmitter. To use the AE in my system, I bought a $40 accessory kit made by Monster Cable that includes a 3.5mm-to-TosLink adapter cable, a 3.5mm jack-to-twin-RCA adapter cable and an extension AC cable.

First, it is important to note what the AE doesn't do. Whether you own a PC or a Mac, the AE works only with iTunes v4.6 or later and is limited to music files that iTunes can read; ie, 16-bit data only. These data, though, can be in any file format that iTunes recognizes, from lossy MP3s at the low-quality end of the spectrum to Apple Lossless and lossless AIF or WAV files at the high end. It is also important to note that the AE functions only at a 44.1kHz sample rate. When you play 32kHz or 48kHz data, iTunes sample-rate-converts the data in real time before sending it to the AE. I tried using the Nicecast utility for OSX ($40) to feed iTunes with 24-bit data and 88.2kHz data from the inexpensive but excellent Amadeus audio-editing program for OSX. High-speed files were played back at half speed and hi-rez data were truncated to 16 bits, according to RME's useful DigiCheck utility for the PC.

Some audiophiles have dissed the AirPort Express on the grounds that its digital output is not bit-accurate. However, I found that this was not the case, that the data appearing on the AE's digital output were identical in the original file. To check this, I compared a WAV file with a duplicate that I had captured on my PC from the AirPort Express's S/PDIF output. I used iTunes on my PowerBook playing a version of the file encoded with Apple Lossless Compression to feed data to the AE. The files were bit-for-bit identical, proving that the AirPort Express is transparent to the music data (as is ALC, for that matter).

 

[Wavelength]

Soundproof

Quote:

Which Firewire or USB methods would you recommend out of a Mac? I have been using TosLink and USB.

It really depends on how it is done. I presently am doing and finishing up Async mode in USB. The benefit is no driver required and the source clock on the dac side can be well maintained to preclude a very low jitter system. Using Firewire will require using a driver. Most of these work on block method. This works really well but does require a driver.

Steve,

Quote:

Used to be true, but with the new "driverless" firmware licensed by Benchmark Media and Empirical Audio, the output is truly bit-perfect, from XP, Vista and MAC. Steve N. Empirical Audio

Actually not true.... I have the Benchmark here and there is nothing fancy about their code or their enumeration. Heck it was identical to mine except they supported 44.1k, 48k, 88.2k and 96k but mine only supported 44.1. So the enumeration was only different by those numbers.

Guys look the enumeration is the only thing making sure that it is bit perfect. As bbrandt said he cannot see bit perfect on the USB analyzer. Me neither...

Ok here is something I posted the other day on another forum. I think this is the case of the differences people hear in PC's applications and between Mac and PC.

Quote:

Again on the PC side I think the big problem is consistency. Better yet... let's look at the way apple does audio (Core Audio): Applications is going to rip a cd it reads a track checks for errors (let's assume none) asks CoreAudio to encode the data and writes to file. Application wants to play a track, it reads the file asks CoreAudio to uncode the data and then play that out xPort. The point is CoreAudio is doing all the work. The application layer does not need to know x, y or z about File type reading writing formats anything. Another Application comes along and reads a file created by the first and walllaaaa it sounds the same. Why because CoreAudio is doing the work not the application, therefore there is consistency across the hardware and software platforms. On the PC side you have programmer that will have to determine how to encode and decode. His compiler use of structure of code everything may effect the way it sounds. Then you have to write to low level driver to avoid the operating system getting in the way. I am not saying that you cannot get PC to sound great. I have, it takes a little more time. But for the average joe who doesn't know or want to know computers I say buy a mac. As for jitter at the software level of a computer. Well maybe the solder fumes are getting to me but WHAT??? Common... ok the data out as we see above can change on a PC, but jitter.... well maybe the PC can effect the jitter on the end product because of processor delays or change of rate which would cause more intrinsic jitter. But I think most of the differences in PC sound comes from the Application layer.

Some of these statements were drawn from a developer of software (I think it was XXHighEnd) saying they could introduce and reduce jitter in their software....

Anyways...Bit Perfect is well crap if you ask me. We can only deal with the data that is given to us and that is almost never bit perfect.

There is nothing in Firewire or USB or Board level for that matter that is going to be bit perfect unless your application is reading the information from a saved file, bypassing ALL the AUDIO drivers and writing directly to the lowest of levels of hardware possible.

Are any of these companies doing that????? no so let's say that Bit Perfect at this time is impossible,

That's not to say this is a bad technology. The data coming out is very good in most cases and heck we are getting updates on a daily basis so this technology for High End is just starting. I think soon we will have the capabilities to do more with Windows and Mac than any tranport dac could ever do.

Thanks
Gordon

 

[audioengr]

Quote:

Originally Posted by DrBenway /img/forum/go_quote.gif Any way I can make a desktop running XP do this...?

Buy a Benchmark DAC-1 USB or an Empirical Audio converter or DAC. The firmware is inside.

Steve N.

 

[DrBenway]

Quote:

Originally Posted by audioengr /img/forum/go_quote.gif Buy a Benchmark DAC-1 USB or an Empirical Audio converter or DAC. The firmware is inside. Steve N.

As I was reading your response, I caught my wallet trying to throw itself out of a window. Oh well, more stuff to save up for.

Thanks for the information. Definately gonna give this a go.

 

[audioengr]

Quote:

Originally Posted by Wavelength /img/forum/go_quote.gif Actually not true.... I have the Benchmark here and there is nothing fancy about their code or their enumeration. Heck it was identical to mine except they supported 44.1k, 48k, 88.2k and 96k but mine only supported 44.1. So the enumeration was only different by those numbers.

What do you mean not true? It's been proven to be bit-perfect with XP, Vista and MAC. If it's identical to yours, then I dont know what this means. Enumeration is another thing altogether. Bit-perfect means exact image of the .wav file at 16/44.1

When I compare the sound from my USB converter to a Squeezebox, both having gone through my Pace-Car reclocker, they are identical. The Squeezebox is definitely bit-perfect. The tests that have been done on the firmware with USB compared the output against the original file content. They were identical.

Steve N.

 

[audioengr]

Quote:

Originally Posted by Soundproof /img/forum/go_quote.gif I'm presently using Airport Express to port music to my Grace m902 DAC/Headphone amp. A TosLink cable goes from the Airport Express to the DAC. Very convenient when I want to do playback from my Laptop. Is it bit transparent?

Of course it is. All networked and wireless networked devices will do bit-perfect. If not, then the data to your network printer would be hosed too....

I have a lot of experience with both the Grace and the AE, since I do my own version of it called Off-Ramp Wi-Fi. It has one significant problem: the device that it uses to output digital data streams is the PCM2705. This device uses a frequency synthesizer internally rather than a fixed master clock like the Sonos and Squeezebox. It multiplies a 6MHz clock up to 48 MHz and then "builds" the clock that it needs for each sample-rate from this. It is a digital/phase locked loop of some sort, with the usual filtering. It also has to reconcile the data rate on the USB with the proper output rate. The jitter from this is rather high, even if the clock is improved significantly. No way to get around it. It can get a LOT better with mods, but nowhere near what you can do with a Squezebox or Sonos.

Steve N.

 

[Wavelength]

Steve,

Quote:

What do you mean not true? It's been proven to be bit-perfect with XP, Vista and MAC. If it's identical to yours, then I dont know what this means. Enumeration is another thing altogether. Bit-perfect means exact image of the .wav file at 16/44.1 When I compare the sound from my USB converter to a Squeezebox, both having gone through my Pace-Car reclocker, they are identical. The Squeezebox is definitely bit-perfect. The tests that have been done on the firmware with USB compared the output against the original file content. They were identical. Steve N.

Proven by who? Steve if the application/driver is not bit perfect then how can the dac be?

By identical how are you testing this? with your ear?

Get a USB analyzer and any real testing equipment and see. All's the firmware does is pass the data it is sent. The enumeration tells the computer how to send it. There is no magic here. Heck there wouldn't be any difference between say a TAS1020 and a PCM2706 for that matter.

Quote:

I have a lot of experience with both the Grace and the AE, since I do my own version of it called Off-Ramp Wi-Fi. It has one significant problem: the device that it uses to output digital data streams is the PCM2705. This device uses a frequency synthesizer internally rather than a fixed master clock like the Sonos and Squeezebox. It multiplies a 6MHz clock up to 48 MHz and then "builds" the clock that it needs for each sample-rate from this. It is a digital/phase locked loop of some sort, with the usual filtering. It also has to reconcile the data rate on the USB with the proper output rate. The jitter from this is rather high, even if the clock is improved significantly. No way to get around it. It can get a LOT better with mods, but nowhere near what you can do with a Squezebox or Sonos.

Actually the PCM2705 uses a 12MHZ crystal or clock and multiplies it to 96MHZ see the figure on page 7. The SpAct Audio Clock Recovery I would have to agree is pretty bad in the jitter department. I found that this chip and the other PCM27xx series chips seems to suffer from the jitter which is caused by the SigmaDelta dac and output. They seem to effect the power supply and master clock (noise wise) which in turn causes more problems. The problem is there is no way to really turn this off.

Many of the newer computers use USB audio controllers inside. Therefore many of these will have more problems with jitter as compared to more bus oriented parts. You can usually look at the USB bus (USBView on the PC or System Profiler on the MAC) to determine if your computer is using a USB or Bus oriented controller.

Thanks
Gordon

 

[Soundproof]

Quote:

Originally Posted by audioengr /img/forum/go_quote.gif Of course it is. All networked and wireless networked devices will do bit-perfect. If not, then the data to your network printer would be hosed too.... Steve N.

I trust you read on, since it was a rhetorical question, with the answer supplied by Stereophile and John Atkinson, in the excerpt I posted from the magazine!

 

[audioengr]

Quote:

Originally Posted by Wavelength /img/forum/go_quote.gif Proven by who? Steve if the application/driver is not bit perfect then how can the dac be? By identical how are you testing this? with your ear?

No, the data was converted from USB to S/PDIF and then S/PDIF back to USB. Bit identical. It was done jointly by the developers and Benchmark engineers. I would not have paid a small fortune to license it if it wasn't. The boys that developed this are a clever lot. Took them over 2 years to do it.

Steve N.