USB to SPDIF conversion

[recordist]

Hi

I'm new to Head-fi and almost as new to computer audio so please be patient.
I own a Fostex FR2-LE location recorder and use it to primarily to record piano music and birdsong. The recorder allows recording of .WAV files at 24/96 onto flashcard media. I download the 'full' cards onto my laptop. I am keen to purchase a MFV-DAC to link the laptop to an amplifier, however, if I use USB, the DAC downsamples to 16bit before upsampling to 192.

My question is: does the conversion process in a USB to SPDIF converter affect the signal in any way-in other words can I get away with a cheapie product for this to produce SPDIF to feed the DAC? My understanding is that many USB to SPDIF converters also contain DACs and headphone outputs and I don't want to spend money on these part of the kit if I am going to be using it simply to convert USB to SPDIF.

I intend to feed the V-DAC to an Arcam amplifier connected to Linn-Index speakers. By playing directly from the Fostex to this set-up I can hear a clear difference between recordings made at 24/96 vs 16/44 and in transferring to CD I seem to lose some of the texture and ambience of the recordings-hence my desire to play the .WAV files directly from the laptop.

 

[Roseval]

Quote:

Originally Posted by recordist /img/forum/go_quote.gif I am keen to purchase a MFV-DAC to link the laptop to an amplifier, however, if I use USB, the DAC downsamples to 16bit before upsampling to 192.

Technically: your DAC won’t do any downsampling, it will simply reject anything > 16/48.
But your OS will take care of the SRC.
SRC is not a trivial thing to implement so you might lose some quality.
You might consider buying a DAC supporting 24/96 over the USB instead of the VDac
The Well Tempered Computer

 

[recordist]

Many thanks for this reply-particularly for correcting me on what the DAC does to a 24/96 signal received via DAC! Using a DAC which enables 24/96 input via USB would I require me to purchase a significantly more expensive DAC than the Musical Fidelity V-DAC (which I understand is very good and well-suited to piano recordings-it is also small and portable).

Sorry to be ignorant-but what is SRC? (is it the protocol for converting a USB signal into an SPDIF signal?). I was thinking of the M-audio transit as a possible interface between my USB port and the DAC but wonder if adding extra electronics might nullify any gain in quality by being able to import a 24/96 signal into the DAC.

What puzzles me is that the line out pre-amplifier on the Fostex is actually pretty poor, and yet I can definately hear an improvement in 24/96 over 16/44 recordings with it. I would be surprised if the DAC within it is capable of properly dealing with a 24/96 signal-so is it possible that a 24/96 signal sounds better played at 16 bit quality than a signal originally recorded at 16 bits. A lot of questions I know!

 

[recordist]

Many thanks for this reply-particularly for correcting me on what the DAC does to a 24/96 signal received via DAC-this should read via USB-sorry!

 

[Roseval]

Sorry, SRC=Sample Rate Conversion eg from 96 to 44.1

Quote:

and yet I can definately hear an improvement in 24/96 over 16/44 recordings with it.

Might be a matter of headroom, if you record at 16 but leaves a margin of 20 dB (approximately 3 bits) headroom you effectively record at 13 bits.
Do the same with 24 and you are recording with 21 bits.
More details: The Well Tempered Computer

I know the M-audio from hearsay only but it does have a good reputation.

 

[transient orca]

Sample rate converter is a digital signal processor (specialized computer chip).

Music streamer II also does usb 24/96. It''s only $150.

 

[audioengr]

The difference in USB to S/PDIF converters is jitter, which is affected by all sorts of things in the design and system, even the S/PDIF cable. So the answer is: you get what you pay for.

You can read about jitter here:

jitter

You can read about S/PDIF cables here:

spdif

The best USB converters use async USB protocol, as this can result in the lowest jitter. However, like all audio products, the design, part choices and implementation is critical to achieving a stellar result.

Steve N.
Empirical Audio

 

[Hybrys]

Wait a moment, are you guys trying to recommend he get a different DAC than his V-DAC instead of just offering a solution? <_<

Look into the M2Tech Hiface. It's a simple and extremely effective USB to SPDIF converter that can run at 24/192. (And can output at 24/96, 16/44.1, etc. without affecting the track.)

 

[recordist]

Thanks everyone for your advice. Aren't DACs such as the V-DAC supposed to be able to compensate for jitter?

 

[Roseval]

I'm afraid the answer is no. It can reduce it but not eliminate it completely.
One day I came across a post that sums it up nicely

Quote:

There are a few main techniques for dealing with interface jitter: Ignoring it altogether. The interface itself. Using a PLL to filter the interface jitter, providing a cleaner version of the clock reconstructed from the interface to the DAC. Using an Asynchronous Rate Converter ( ASRC ) to manipulate the data such that it "fits" in the two clock domains Using the DAC clock to drive the clock in the the source ( "asycnchronous" modes - async USB, async firewire, most ethernet solutions, some kind of link from DAC to source ) The last is the best - assuming the same level of competency is applied in all cases, but all bets are off otherwise...

Bit Perfect Jitter

 

[Kobra]

Do as Hybrys said and look at the M2Tech Hiface, it's a small USB to S/PDIF converter. It looks like a small memory stick. It will allow you to use "kernel streaming" from your PC to your V-DAC, this will not alter your original recording. The Hiface is a "cheap" ( not that expensive) solution to your request. There's a lengthy thread about it in this forum.

 

[regal]

If you are set on converting these wave files to 16/44.1k you need to use build a DAW, use R8Brain Pro for the downsample then Samplitude plus Ozone VSt to dither. Much cheaper to just buy the Hiface.

 

[recordist]

Thank you everyone who has recently added advice. It has been extremely helpful. As a consequence of what I have found out I am considering:

(1) buying V-DAC and hearing how it sounds using the USB input alone.
(2) consider buying the Hiface as a possible upgrade so that 24 bit files can be played at their full resolution.

This is based on the assumption that there is a lot of quality loss when a 24/96 file is burned onto a CD-R which necessitates that Windows Media player downgrades the file from 24/96 to 16/44.

Please tell me-am I correct in thinking that when I burn files recorded at 24 bits onto a blank CD-R, they are no longer .WAV files and are actually inferior to 16 bit .WAV files, because WAV files are intrinsically better?

I would therefore expect the quality of playback from from 16/44 files burned, using Windows media player onto a CD-R burned from 24 bit .WAV files to be inferior to either 24 bit .WAV files played back from a hard-drive through the 16bit USB part of the V-DAC or 16 bit .WAV files played back through the same USB connection on the V-DAC.

I realise that the quality of the compact disc player has a role to play-let us assume that the DAC in the compact disc player is as capable as the V-DAC.

 

[Roseval]

You say CD-R=CD Rom=a data disk.
This can contain any data in any format.
You probably means burning a audio CD (redbook), this requires downsampling to 16/44.1 otherwise it won’t play on a CD player.

The contents of a WAV file is uncompressed PCM, the content of a audio CD is uncompressed PCM. They are about as identical as one could get.

Will there be a loss of quality when downsampling?
Almost all recording today are made with 24 bit and often a higher sample rate than 44.1
Do all CD’s sound bad?

 

[recordist]

So that's me put in my place then...(!).

Hadn't realised that files on a CD were still .WAV files. I do of course realise that many commercial CDs have excellent sound-however I did not assume that using Windows Media player on a home PC would produce exactly the same quality of result that a record company would carry if they were they producing a commercial from the same .WAV files (not likely in my case!). But maybe a .WAV file is just a .WAV file!

The output pre-amp on my Fostex FR2-LE is reckoned to be no great shakes and can sound a bit harsh and unmusical at times-and in practise it isn't feasible to use it to play back anything other than my most recent recordings (it can only play from flashcards which are an expensive storage medium). However, recordings made at 24/96 and played back through this thing do sound far more as if one is in the same room as the piano (the resonance and 'life' of the sound is preserved) compared to the same files played back through from a CD made from the same (albeit downsampled) files. The CD players are of good quality (including an Arcam Alpha 5) so I am puzzled, particularly as I don't suppose that the Fostex recorder has a D/A converter that can play 24/96 files without downsampling. (16 bit recordings played back through the recorder from the flashcard don't have the atmosphere or immediacy of 24 bit recordings).