DA7: AUX Return 1/2 S/PDIF: 20 or 24-bit

[Guest]

I am looking at equipment for my home

recording studio. With regard to the

the Panasonic DA7, I am concerned about

loosing bits if I connect a digital

reverb to the DA7's S/PDIF AUX 1/2

Return.

 

References:

 

- EQ Magazine, April 1999, page 155:

 

"AES can contain 24-bit audio, but

S/PDIF can only contain 20-bit audio

because the extra bits are used for

copy protection and sample rate

flags."

 

--> This makes me think that I will

have to dither my 24-bit signal

to 20-bit for the AUX Send 1/2

and that the AUX Return 1/2 can

only receive 20 bits.

 

 

- EQ Magazine, April 2000 Issue, page

p92, bottom "IEC958 Type I or S/PDIF?"

 

"IEC958 Type I (a.k.a. AES/EBU)"

"true S/PDIF (a.k.a. IEC958 Type II)"

 

--> This gave me hope that S/PDIF

CAN handle 24-bits in both

directions.

 

 

- Panasonic "Digital Recording Mixer

DA7" 3 page glossy, P-447b and

the DA7's User's Guide, page F-4.

 

Aux Send/Return 1/2:

IEC958 consumer (S/PDIF),

rca pin jack

 

Rec Out:

IEC958 professional (AES/EBU),

xlr-3

 

--> But this makes me think that the

AUX Send/Return only handles

20-bit because they are 'IEC958

consumer'.

 

 

- DA7's User's Guide, section 12-3,

pg 12-16

 

- It appears that Dither can be set to

 

- Off : in this case the DA7 will

output 24-bits to the

S/PDIF cable and what ever

device is at the other end

of the cable (pg 12-15)

 

- On : with this, dithering takes

place and you specify the

word length from 23 down to

16 bits.

 

--> This implies that at least the

AUX Send can transtmit 24-bits.

 

- T.C. Electronic M3000 User's Guide,

pg 15

 

S/PDIF is sometimes limited to 20

bits. All TC equipment output 24 bit

on S/PDIF outputs, and process 24-bits

from S/PDIF inputs.

 

It's S/PDIF output can be configured

to output what they call the

professional AES/EBU standard OR the

S/PDIF consumer standard.

 

--> This is good news, at least for

this reverb. It will receive

and send 24-bits of audio. No

need to worry about losing bits.

 

I think that I can have the following

SIGNAL FLOW:

 

- DA7 with 24-bit signal,

- its AUX SEND 1/2 sends 24-bit audio,

- to the M3000 S/PDIF IN which will

process the 24-bits,

- the M3000 will send 24-bit audio

- to the DA7 AUX RETURN 1/2

 

- At this point, I don't know what the

DA7 AUX Return 1/2 will do with

24-bits because the specification says

it is IEC958 consumer, not

professional.

 

 

Questions:

 

1: IEC958 consumer (s/pdif) vs DA7

outputing 24-bits.

 

If I had to guess, I would say the

'IEC958 consumer' means that there

are:

 

- 20 bits of audio

- 4 bits for copy protection and

sample rate flags.

 

But this would contradict the info in

section 12, for the AUX Send 1/2, at

least, which says one can have 24

bits of audio.

 

Is 'IEC958 Consumer' 24-bit or

20-bit?

 

 

2: Does the DA7 ever output the

following on Aux Send 1/2:

 

- 20 bits of audio

- 4 bits for copy protection and

sample rate flags?

 

Maybe only when dither is 20?

 

This is configurable on the M3000.

 

 

3: What does the DA7 expect to receive

at Aux Return 1/2? I.e. what

standard does it support, the

professional AES/EBU standard 24-bit

OR the S/PDIF consumer standard that

is documentation implies which I

think migh be 20-bit?

 

The T.C. Electronic M3000 send's

24-bits on its S/PDIF output. Is the

the DA7's AUX Return going to accept

all 24-bits of audio and therefore I

will never lose any bits through the

AUX Send/Return interface?

 

------------------

 

Thanx for the help,

 

Bill

[Mr. G]

Hi Bill,

 

Your post is exactly why I wrote the sidebar in EQ that you are referencing. It's my (admittedly dim) hope that manufacturers will read it (and posts like this) and try to standardize how they refer to coaxial digital connections. To Alesis' credit (your quotes came from the MasterLink review), they're specific about the format they're using. Other manufacturers aren't as specific.

 

The good news is that your system will likely work regardless. The question is whether you'll get full 24-bit signals.

 

Perhaps a DA7 owner (Craig?) knows the answer to your Aux resolution question....

 

------------------

Mitch Gallagher

Editor

EQ magazine

 

[This message has been edited by EQ_Editor (edited 06-10-2000).]

[Anderton]

Originally posted by EQ_Editor:

Hi Perhaps a DA7 owner (Craig?) knows the answer to your Aux resolution question....

 

Hey Mitch, thanks for adding your expert advice. Here's the deal with the DA7:

 

The aux analog converters are 20-bit, unlike everything else in the DA7, which uses 24-bit converters.

 

The SPDIF digital connections can indeed handle a 24-bit data stream. Basically, the DA7 SPDIF works just like the AES/EBU, except with different levels and such.

 

This is a mixed blessing. The good news is that you get true 24-bit operation. The bad news is that some older gear doesn't know what to do with SPDIF signals that include 4 extra data bits. I don't know of any specific gear, but apparently this can be an issue with any gear that passes 24 bits through SPDIF.

 

Frankly, by the time you're done with the mix, it probably won't matter whether what's patched into your aux bus is 20 or 24 bit anyway.