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mazurek
2005-08-30, 12:58
I am sending the output of the squeezebox to a behringer digital equalizer to a benchmark dac. I'd like to make sure I am getting the best possible quality. Is the digital output of the squeezebox always 24 bit resolution, or does it depend on the source file?

I think the behringer uses the input format as the output format, so it would make sense that starting with 24 bits would be better before equalization. Also the equalizer has a dithering setting, should this be on or off with the squeezebox output?

pfarrell
2005-08-30, 13:12
On Tue, 2005-08-30 at 12:58 -0700, mazurek wrote:
> I am sending the output of the squeezebox to a behringer digital
> equalizer to a benchmark dac. I'd like to make sure I am getting the
> best possible quality.

The audiophile answer would be to not use the equalizer. The fewer
things in the chain to mess it up, the better.

A lot of audiophile preamps and integrated amps don't even have
bass and treble knobs for the same reason, fewer things to mess
up the music.

> Also the equalizer has a dithering setting, should this
> be on or off with the squeezebox output?

Dither is critical every time you reduce the number of bits in
a signal. If you are feeding the Benchmark and it is doing 24 bit
processing, there is no reduction in the number of bits.

But you may be doing something. If you multiply two 24 bit numbers
together, you get a 48 bit answer. Or more properly,
up to a 48 bit answer depending on what you are multiplying.
If you then map that answer back to 24 bits, you need dithering.

BTW, the Behringer brand is not normally considered in the same
class as the Benchmark DAC-1. They have good products at very good
prices, but audiophiles sometimes scoff at the brand.


--
Pat
http://www.pfarrell.com/music/slimserver/slimsoftware.html

Mike Hanson
2005-08-30, 13:22
Is the digital output of the squeezebox always 24 bit resolution, or does it depend on the source file?
Ripped WAVs from CDs are 16-bit, so 24-bit will not happen.

I'll second Pat's comments: equalizers are generally frowned upon in the audiophile world. I would skip it, unless you have an unbearable desire to twiddle knobs.

-=> Mike Hanson <=-

dean
2005-08-30, 14:20
On Aug 30, 2005, at 1:22 PM, Mike Hanson wrote:

>
> mazurek Wrote:
>
>> Is the digital output of the squeezebox always 24 bit resolution, or
>> does it depend on the source file?
>>
> Ripped WAVs from CDs are 16-bit, so 24-bit will not happen.
Yes, but... MP3 is a lossy encoding. Our MP3 decoder does generate
24 bits of output.

Then decoded MP3 and FLAC audio may have a volume adjustment applied
to it with 24 bits of accuracy.

The D/A converter then gets 24 bit output. S/PDIF output will be
converted back to 16 bits.

seanadams
2005-08-30, 19:06
S/PDIF output will be
converted back to 16 bits.

Correction: we output 24-bits to both the s/pdif and the internal DAC.

quadguy
2005-08-30, 20:36
For what it's worth, I use the Behringer EQ completely in digital mode, and I've found it to be not only totally transparant but to have a very decent DAC to boot. I use the SB's digital out to the DEQX 2496 and I find it an absolute dream - and find that MP3's on shoutcast radio stations (128k or higher) sound surprisingly good.

The audiophile answer to not use an EQ applied more when EQ's were in the analog domain with all their attendant filters and electronics - when in purely digital mode all it does is alter the bitstream, I can find no lack of transparancy via my Quad electrostatics at all and that says a lot. When I switch back to non-eq mode now and hear the bass bouncing all over the room, I quickly realize that whatever slight loss in transparacy there may be, it pales in comparison to the room problems it solves!

I'm still absolutely amazed that MP3 streams at 128k are as listenable as they are via the SB. Many 128k stations are not that good - perhaps they play comprimised MP3 sources or don't have as good an encoding scheme as other stations, but those stations that play CD's at the source with good encoding to 128k sound surprisingly good. I'm getting a faster modem to tap into the 320k bitstreams, very interested to hear how they sound.

You'll love the Behringer + SB - and if you want a different sound, you can add a DAC onto the end of the Behringer - perhaps a tube based DAC. True, you're adding some jitter possibilities, but I've found the jitter from the SB to the Behringer negligable - it sounds fantastic!

quadguy
2005-08-30, 20:54
Whoops! Forgot to answer your actual question - I assume the "Dither" setting you refer to is on "Page 2" of the "I/O" menu? Mine is set to 24 bit and sounds great, although I haven't tried turning it off. I think 24 bit is the factory default. However I don't know if it even matters if the Behringer is not feeding an external DAC.

I'd sure love to hear the Benchmark on the end of my Behringer - now there's an empirical mod for the Benchmark too, but man is it expensive. Never seems to end.

pfarrell
2005-08-30, 20:59
On Tue, 2005-08-30 at 20:36 -0700, quadguy wrote:
> The audiophile answer to not use an EQ applied more when EQ's were in
> the analog domain with all their attendant filters and electronics -
> when in purely digital mode all it does is alter the bitstream,

if you like it, use it. Use your ears, not mine.

But applying EQ without impacting phase is very hard.
It takes very fancy algorithms and lots of computation.
Impacting some frequency's phase and not others can
have serious impact.

Many of the EQs used in professional studios and mastering
houses are not phase neutral. Some have specific "color" that
can be used as an effect. Often times, it is a good effect.
Often the specific color of the EQ means people pay serious
money to get the exact Class-A discrete circuit, API, Neve
and other companies made or make EQs that cost thousands of
dollars per channel.

As I've posted before, humans are much more sensitive to
phase than they are to frequency response.

The bitstream is the music. Altering the bitstream
changes the music.


--
Pat
http://www.pfarrell.com/music/slimserver/slimsoftware.html

quadguy
2005-08-30, 22:00
Agreed, it doesn't attempt to handle phase relationships as would an expensive Tact unit for example. But I only EQ bass and the effects on phase from say 250Hz down are far less evident than if one were EQ-ing the critical midrange region. I bought it to take the boom out of the room, and it does that with no apparant negatives, far better than my expensive ASC tube traps ever did. With my Quads + Behringer, I can hear soundstage info pasted to the left/right walls of my 23' wide room and a smooth spread of sound from stage right to left - so if phase is reflected in imaging, there's no problem when not EQ-ing above the bass. Abient recordings image waaaay outside the speaker boundaries, even on some MP3 stations, and dance and techno are a pure acid trip. This all happens with the Behringer's internal DAC which was just a pleasant surprise and bonus for me - I wasn't even sure it had a DAC when I bought it, I thought it was a purely digital device considering it's cheap price.

There are a few professional reviews out there that compare it's digital to it's analog mode, and although they generally say it's fine in analog mode, but the digital mode is far superior - of course in analog mode, you have to undergo an additional A/D conversion to get the advantage of the Digital EQ, so it's no wonder things are getting rough when you go that way.

When I run the digital signal through the Digital EQ with no EQ settings - all flat - there's no difference at all. When the EQ settings are changed to equalize the bass the difference in quality of sound overall is so massive once the room-boom is gone, trying to split hairs over minute changes in transparancy is near impossible, and pointless really compared to the overall improvement. Them's my ears anwyay, in my room.

The reason I mention this is that after having suffered with room problems for the past 15 years of my audiophile career, I've never found anything so remarkable in it's level of improvement for so little money - $300 US street price - I'd hate to see others pass up such a bargain if the have roomboom problems. My ASC tube traps were thousands and thousands of dollars, and so terribly ugly - they're long gone now, got back fifty cents on the dollar for them, for a net loss of many thousands.

pfarrell
2005-08-30, 22:35
On Tue, 2005-08-30 at 22:00 -0700, quadguy wrote:
> With my Quads

I'm in serious lust mode for some Quads. They have sounded great
every time I listen to them. But they are too big, require too big
a room, and totally flunk the WAF in my world.


> There are a few professional reviews out there that compare it's
> digital to it's analog mode,

Got any URLs? I find "professional audio" trade magazines to have
even less credibility than the high-end audiophile stuff. Most of them
do not really review stuff. One of my big shocks getting into recording
was that I've been reading the car buff books for 25+ years. They
regularly do comparisons with four or more cars aimed at the same
market. The "Recording" and "Mix" and the like never compare and
rarely make more that "you should consider this" as a comment.

> The reason I mention this is that after having suffered with room
> problems for the past 15 years of my audiophile career,

Room problems are serious and I think under considered.
Guess it is easier to buy a $400 interconnect than fix a
listening room that is 8x8x24.

Real Traps, sold by Ethan Winer, actually are big enough, and
are really engineered to stop the 80 to 300 hz standing waves that
typical home listening rooms are cursed with. They are not cheap,
and don't pass WAF for me. Acoustic treatment is tough. The random
"skyline" diffusers work, but at frequencies that are usually not the
major problem. To work at room standing wave frequencies, each "step"
has to be about four inches, and you need to cover many feet.
Cue Recording Studio has a suitable low frequency diffuser in
their "A studio" that you can see in the background of
http://www.cuerecording.com/aroom.htm


There is no way such a treatment will exist anywhere near
my living space. In my studio, I use lots of old sofa, etc.

--
Pat Farrell PRC recording studio
http://www.pfarrell.com/PRC

mazurek
2005-08-30, 23:04
Thanks for the info everyone. Looks like I can be sure that no resolution is being lost relative to the original when I equalize it. (My calculator says for a 24 bit signal, I've got 48dB of headroom before I lose resolution). I agree with quadguy, there is such a noticable improvement in bass response that the equalizer is definetely worth it.

The expensive Tact room correction gear has been raved about by audiophiles, but even its 1500 dollar model doesn't have phase correction. I spent all my money on the dac so I'll have to trust the behringer.

quadguy - I don't know if the benchmark is any different than any high quality dac, but its jitter immunity insulates me from high end transport voodoo, and its one component I know I don't need to upgrade.

Thanks for the explanation of the dither. I agree with you pfarrell after the dac I try to keep it as simple as possible. I use the preamp in bypass mode, and have super short interconnects.

quadguy
2005-08-30, 23:25
Here's the one that compared analog and digital operation - this is the DEQX's predecessor - the 8024 - it was double the price then, and had nowhere near the digital advances of today, yet he rates it as "value for money" of 200% ! It's one of the better reviews because he really concentrates on room problems, which is what it's all about.

http://www.enjoythemusic.com/magazine/equipment/0101/behringer8024.htm

I've had the ESL 57's for 15 years, although in that period I also had the 989's briefly. Waaaaay too much bass on the 989's, had to sell them - I'll never live in a room big enough - plus they didn't have the midrange immediacy of the 57's, nor the low volume full fidelity. The ESL 57's took me out of the speaker chase 15 years ago aside from trying the 989's, never would I replace them. Plus with even the old solid state Quad 303 they're great - safely run too - but low power tube amps, which I also have, are great - but not so much better that I want 10 roomheating tubes any more.

But you are right about the room required for Quads - mine are 8' from the rear wall, and they absolutely have to be at least 4' and even then the bass can be boomy. 8' is awesome. The WAF on mine is good though - because they sit between rooms - between the living room and the dining room, so they're not really visible when in the LR, and certainly aren't in the way. What a break! BUT, the left quad is only 1' from the wall to the left of it, and there's a wall and sofa between them which collected a lot of bass. Plus, although I sit 13' away, there's a wall right behind my listening couch, and corners to either side albeit 23' apart - corners are corners. Even with this setup, there was unacceptable bass boom clouding the whole thing - it was awful.

"Room problems are serious and I think under considered" - you're soooo right they're underconsidered - here's a perfect example. I moved from a 26x40 room to my current 23x13 room - plugged the same stereo in, and it was a COMPLETELY different stereo - no roomboom in the 26x40, massive roomboom in 23x13. I couldn't believe the difference - and it was the worst on CD. I took a chance on the Behringer and wow - what a difference. For my tuner it wasn't so necessary because radio stations EQ a lot already - but CD was awful in my new room. Even with good MP3 streams with the SB, I prefer to use the Behringer. PLUS, living in a condo, it's very good for neighborly relations.

As for the real traps, I agree about the WAF - they and others don't even pass the MAF (Male Acceptance Factor) for me, much less the WAF. I used to have ASC tube traps, 12 roomlens, 2 shakti's, and other crap all in one room. I couldn't stand it - that's no environment for listening to music, I want to be in a nice room, with a glass of wine or a cup of tea - not some hobby room littered with stuff like that. If I was smart, I'd have bought the Tact back then, even though it was about $4500 US - I'd have never had to go through the room treatment nightmare, and it would have worked better anyway. If I'd known I'd end up spending that much in room treatment in the long run, I'd have taken out a loan and got the Tact.

"There is no way such a treatment will exist anywhere near
my living space" - agreed, that's where I am now. Put it this way - next time you're considering a fancy $300 interconnect or some such audio tweak for hundreds of dollars - ask youself - why not give the Behringer a shake? It will give you an education on your room that's worth the price alone, the fact that it sounds so good is just a bonus. You can also buy a microphone so it will auto-EQ your room, but I won't dare EQ above bass - that's too sensitive an area to the ear. Another eye opener for me was the Creek OBH-12 passive preamp - that's what the Behringer feeds and it's an awesome combo (the Behringers output is VERY VERY high as per pro audio gear, so the Creek probably made things far better just because of that).

Mike Hanson
2005-08-31, 06:38
Correction: we output 24-bits to both the s/pdif and the internal DAC.
Interesting. So what happens when I'm outputting it to a 16-bit NOS DAC?

-=> Mike Hanson <=-

seanadams
2005-08-31, 12:37
Interesting. So what happens when I'm outputting it to a 16-bit NOS DAC?

-=> Mike Hanson <=-

The additional resolution is just ignored by the DAC - it works like a 16-bit interface.

sbjaerum
2005-08-31, 23:19
The additional resolution is just ignored by the DAC - it works like a 16-bit interface.

I assume then that the 16 bit DAC uses the 16 most significant bits of the 24 bits transferred by S/PDIF.
How does digital volume adjustment work in this scenario?

Steinar

Nicola Fankhauser
2005-09-08, 10:56
hi sean


Correction: we output 24-bits to both the s/pdif and the internal DAC.

I just got my SB2 two days ago and tried today connecting it to my DIY DAC (based on the DA1543N DAC, http://www.dddac.de), which works wonderfully with the digital coax output of my Creek CD player.

however, SB2 seems to send 24bit data even if I play back 16bit data (like you state above) - is there any possibility (hardware-wise) to force it back to 16bit?

I will contact the author of the DIY DAC design and ask about a new receiver-chip, which maybe could solve this problem as well...

thanks & regards
nicola

seanadams
2005-09-08, 13:00
however, SB2 seems to send 24bit data even if I play back 16bit data (like you state above) - is there any possibility (hardware-wise) to force it back to 16bit?

How are you determining this?

seanadams
2005-09-08, 13:45
To clarify: there is no difference in the data format for 16-bit versus 24-bit over s/pdif.

If you play 16 bit with volume set to 100%, you will get the same 16 bits at the output (the 8 least significant bits will be zero).

If you have volume set to some intermediate level then the additional LSBs will be populated accordingly. If your DAC doesn't support 24-bit then they're ignored.

Nicola Fankhauser
2005-09-09, 00:06
hi sean

thanks for clarifying - I wrote to the author of the DAC design and will have to wait for his answer for finding out what really happens there.

so to summarize SB2 sends the following format (certainly a bit more complex in real life):

MSB 0x00 - 0x0F 16 bit data
LSB 0x10 - 0x17 8 bit additional data (all bits 0 if source is only 16bit and volume is 100%)

now I think that the mere *sending* of the 8 zero LSB bits might trouble my DAC - which is only a presumption up to now. the thing is that the used DA chip is so low-end that it only accepts 44.1khz 16bit data, and that the receiver on the DAC might happily decode the 24bit data and sends it as-is (meaning with the 8 zeroed bits) over to the DA chip, which in turn refuses to decode _anything_.

otherwise I have to tell I am very happy with the SB2!

regards
nicola

seanadams
2005-09-09, 00:19
I would be astonished if any 16-bit DAC has a problem with the other 8 bits being populated. BTW here's a good explanation of s/pdif - better reading than the IEC spec.

http://www.epanorama.net/documents/audio/spdif.html

Nicola Fankhauser
2005-09-10, 01:05
hello sean

thanks for helping, it turned out that my DAC was not working properly. I repaired it and it works like a charm with the SB2! first listening tests indicate that in comparison with the SB2 my own DAC reproduces music a bit warmer and "opens the stage" somehow - yet the differences are subtle, difficult to pin-point and I like the sound of the SB2 a lot as well.

btw, is there an explanation why FLAC files sound so much better than MP3 on the SB2 (analog output)? I maybe will try how (high quality, if that exists :) MP3 files sound through my own DAC.

thanks again!
nicola

ceejay
2005-09-10, 11:25
btw, is there an explanation why FLAC files sound so much better than MP3 on the SB2 (analog output)? I maybe will try how (high quality, if that exists :) MP3 files sound through my own DAC.



That would probably be because your FLAC files are lossless - they are converted in the SB2 back into a bitstream which is "identical" to the WAV files you started with. Your MP3s will certainly be lossy - though quite how audible the difference will be depends on the quality of the encoder and the bit rate. There are plenty of people who will say a good MP3 at 320kbits is as good as lossless - but if you're down at 128kbits, say, you'd probably have to be hearing-impaired not to be able to tell.

Ceejay