Fostex VF160 ADAT output

[1hdr4u]

Hi all I'm new here and I have a Fostex VF160 16 track recorder that I've had for years and I mix down my recordings on a Sony mini disc recorder. The VF160 has a ADAT input/output and my Sony mini disc has an optical input. Before I started to use those inputs/outputs I was just mixing my songs from the VF160 to mini disc by way of the analog outputs from the 160 to mini disc. If I start only using the ADAT output from the 160 to mini disc, will the digital quality of my songs be upgraded to full 44.1 kh or full digital quality as opposed to using the analog outputs? The quality of my songs sound the same either way so I'm wondering if there's really any difference. Thanks.

[Tim Gillett]

Sure there will be a difference but it may or may not be audible. The other probably greater source of loss would be the Minidisc itself, which is a lossy format, but again hard to know if the losses would be audible as it depends on what was recorded.

It looks like your Fostex can mixdown to CD via its own burner. Why not use that instead of the Minidisc? You'll avoid the unneccessary conversion steps as well as the Minidisc's compression losses.

Tim

[Hugh Robjohns]

The VF160 has a ADAT input/output and my Sony mini disc has an optical input.

For the benefit of others, it would be worthwhile clarifying that although the ADAT and optical S/PDIF interfaces use the same physical optical connector type (and the same light-pipe fibre optic 'cable'), the way the data is formatted is completely different between these two standards. Consequently they are not compatible -- not least because ADAT can carry up to 8 channels of audio at base sample rates, while S/PDIF can only ever carry two channels.

Fortunately, the Fostex machine allows the its optical ports to be configured either in either the ADAT or S/PDIF formats -- via the SETUP menu. But since you're apparently using this interface successfully, I guess you've already discovered that.

As for the quality issues, Tim has already highlighted the salient points.

Modern A-D and D-A converters are astonishingly good and the losses involved in sending audio via an analogue path are generally negligible and completely inaudible (provided you set the gain structure correctly to avoid clipping).

However, a digital path -- via optical S/PDIF in your case -- avoids any risk of incorrect gain structures and provides a bit-accurate data transfer, so would normally be considered better.

In your case, though, the MiniDisc employs a lossy codec system (ATRAC) which inherently degrades the audio quality through psychoacoustic data reduction techniques. To be fair, ATRAC is a very sophisticated lossy codec -- far more so than MP3, for example -- but some audio information will be discarded through the recording process. The idea of a perceptual codec like ATRAC is that the natural failings of the human hearing system mask the data losses... but that's not always the case.

If your Fostex machine has the CD-R drive installed, then you could make true bit-accurate copies to CD-R and play those on a conventional CD player. That would avoid the losses inherent in the Minidisc codec.

But at the end of the day, if it sounds okay to you then what's to worry about, whoever way you do it?

H

[1hdr4u]

In your case, though, the MiniDisc employs a lossy codec system (ATRAC) which inherently degrades the audio quality through psychoacoustic data reduction techniques. To be fair, ATRAC is a very sophisticated lossy codec -- far more so than MP3, for example -- but some audio information will be discarded through the recording process. The idea of a perceptual codec like ATRAC is that the natural failings of the human hearing system mask the data losses... but that's not always the case.

But at the end of the day, if it sounds okay to you then what's to worry about, whoever way you do it?

H

I guess I'm not up on the recording process of my mini disc recorder. I know it's an old outdated machine, but since it is a digital recorder does it not still record wave files in a 44.1 sample rate which is the same as your average CD? And would the bit rate still be at about 16 bits for the mini disc? How much loss or degrading of the file is there compared to CDs?
Thanks for yo"] help.

[Hugh Robjohns]

...but since it is a digital recorder does it not still record wave files in a 44.1 sample rate which is the same as your average CD?

Same sample rate, but not the same samples -- and definitely not wave files!

The codec is called ATRAC (Adaptive TRansform Acoustic Coding) and it is a fairly sophisticated perceptual codec which analyses the audio signal content, moment by moment, and works out which parts of it the average human can perceive, and which will be masked (in both the frequency and time domains) by other dominant elements. It then keeps the bits it thinks you'll hear, and throws the rest away. It reduces the amount of data to roughly a fifth, encoding the resulting data stream at a bit rate of 292kb/s.

And would the bit rate still be at about 16 bits for the mini disc?

The word-length (not bit rate) of a normal 'red-book' CD is 16 bits. The bit rate is 1411.2k bits/s (44.1 k samples per second x16 bits x2 for stereo).

The bit rate of Minidisc is 292k bits/s -- five times smaller.

How much loss or degrading of the file is there compared to CDs?

In a purely mathematical sense, its a massive loss, as the numbers clearly indicate. However, it's called a 'perceptual coder' for a reason -- and the reason is that if they designed it right (and ATRAC is actually one of the better lossy-codecs), you won't actually perceive any quality loss at all under normal listening conditions, because the losses are effectively all hidden by the infallibilities inherent in our sense of hearing.

You might find these articles helpful:

http://www.soundonsound.com/sos/aug04/a ... 0804-3.htm

http://www.soundonsound.com/sos/aug98/a ... ssion.html

Where lossy-codecs fall over quite quickly is when you start copying the audio between lossy systems. In other words, replay from your minidisc to the computer and convert to MP3, for example Each new stage of lossy data reduction throws away more of the wanted audio, and the quality degrades audibly and quickly which each additional concatenation.

For that reason, lossy-codecs are generally intended only for end-user listening where no further processing or copying will ever be required.... And that's why recording your stereo mix as a red-book CD would be a better choice, technically, than the MiniDisc machine.

H

[James Perrett]

A few years ago I was mixing a song down to Mini Disc from an analogue multitrack tape. I thought I'd done a decent mix but on playback it sounded like the heads were very slightly dirty - the cymbals cut off early and it sounded like there were small dropouts. So I cleaned the heads thoroughly did the mix again - this time listening carefully to the cymbal tails and making sure that there were no dropouts. It sounded good to me but on playing back the MD the cut off tails and dropouts were still there - I realised that they were artifacts of the ATRAC system.

I've not actually noticed quite such serious problems with mp3 coding so I'm a little surprised that Hugh says that ATRAC is more advanced than mp3 as I thought ATRAC was more on a par with the earlier mp2 standard.

[Hugh Robjohns]

The ATRAC coders evolved quite a lot over the years. Can't remember the precise details now, but I think it went through five versions over a few years. The later version was significantly better than the first. This is common with perceptual coders where only the decoder design is fixed. That allows the coder design to be improved as the understanding and model of human perception evolves and improves.

The basic ATRAC codec is more sophisticated than mp3 (or 2). It uses a more sophisticated arrangement of filter bands to analyse the spectral content, but importantly it also uses temporal masking techniques, too -- something which is absent from the MPEG codecs.

ATRAC is actually closer to Dolby's AC3 (Dolby Digital) in concept than MPEG, and Dolby actually ended up suing Sony for patent infringements and now collect royalties for ATRAC codecs. ATRAC is used in the SDDS film soundtrack system as well.

H

[1hdr4u]

Same sample rate, but not the same samples -- and definitely not wave files!

The codec is called ATRAC (Adaptive TRansform Acoustic Coding) and it is a fairly sophisticated perceptual codec which analyses the audio signal content, moment by moment, and works out which parts of it the average human can perceive, and which will be masked (in both the frequency and time domains) by other dominant elements. It then keeps the bits it thinks you'll hear, and throws the rest away. It reduces the amount of data to roughly a fifth, encoding the resulting data stream at a bit rate of 292kb/s.

H

Wow,..I guess I really didn't know how much loss there was in recording to my old Sony mini disc. At least the good news is that the quality of the recordings on the mini disc still sound good to the human ear. I know my machine is old and out dated, but I should point out that I use it to do my performances since I do shows where I sing to background music that I've created. I like the benefits of the Sony mini disc because you can rewrite song files on it over and over again, arrange the songs in any order you want or delete them and put new songs in and you can name your songs all on the same machine. I wish there was some kind of a CD player/recorder that I could buy that did all those same things but I haven't found anything that is similar to the benefits of the mini disc recorder/player. If there is I would like to know what it is.
Thanks again.

[Hugh Robjohns]

Pretty much any modern file player -- even an iPod -- will do that, and most will work with full-fat wave files. Easiest if you can record into a computer and manage files from there, but some will work standalone like you old MD machine.

H

[Mike Stranks]

I used to use a 'hi-fi' size Sony minidisc for playing back FX in 'live' situations. The 'cue to start of next track' was invaluable in that context.

These days I use free software on a small laptop. Even better... as you can edit the cue list on the fly if you have to.

... and ATRAC did get better... I recall that the only track on which I could spot the difference was a well-recorded classical piano and listening through very good headphones. Even then differences were very very slight.