Need Help Getting Started in Computer Audio

[duke43j]

Hi everyone. I just stumbled upon this website and found it very interesting. I’ve been a hi-fi nut for many years, but I only recently have been able to afford a decent rig (just when my hearing is starting to go). I recently purchased a Squeezebox 3 and absolutely fell in love with the convenience of having all my music at my fingertips. The sound of the SB3 is surprisingly good considering its cost, but it doesn’t compare to my Rega Apollo CD player. So now I’m on a crusade to find out how to get the convenience of the SB3 without sacrificing sound quality. After reading some of your comments it seems that this may be the place I can get some help.

 

My first thought to improve sound quality was to feed the digital (spdif) output of the SB3 to a decent DAC. My local hi-fi shop was kind enough to loan me a used Mark Levinson 36s DAC for a few days. This is an older DAC, but highly rated in its day. With the ML DAC in the system the sound quality improved, but it still wasn’t up to my Rega CD player. Just for kicks, I connected the spdif output from a decidedly lo-fi DVD player to the ML DAC. The sound was noticeably better than the SB3 – DAC combination. This absolutely baffled me! Why would the digital bits from a DVD player be any different than the digital bits from the SB3?

 

I’ve got several theories, but I don’t really like any of them:

1) The PC software that does the FLAC compression somehow drops the least significant bits during the arithmetic.

I find this hard to believe because it would be so easy for the software designer to check (i.e. by comparing the original file with the compressed/decompressed file).

 

2) Bit errors get introduced in my 80 foot length of Cat 5 cable from my PC to the SB3.

I don’t think this is happening because I’m not hearing any dropouts or skips in the music (due to packets being discarded for failing the error check). Besides, the entire tune is affected (i.e. narrower soundstage, notes don’t “ring” as much, etc.). It’s not something that happens just now and then.

 

3) The software in the SB3 somehow drops the LSBs during its processing to convert the FLAC/ethernet data to PCM/spdif data.

This seems to be the most plausible theory, but I would discount this for the same reason stated above.

 

4) The SB3 introduces jitter in the spdif output that is beyond the ability of the ML DAC to handle.

I find this hard to believe because the ML DAC has excellent jitter suppression. It has a FIFO that accepts the incoming data stream and clocks it out using a very stable clock. Besides, the SB3’s internal DAC seems to handle the jitter reasonably well without the elaborate jitter suppression scheme of the ML DAC.

 

Does anybody have an idea what is happening here? From previous posts it appears that some of you think the Squeezebox is the culprit, but I can’t figure out why. I would hate to spend money on another music server or Mac without having some confidence that it will be any better than what I’ve got.

 

 

[audioengr]

"Why would the digital bits from a DVD player be any different than the digital bits from the SB3?"

 

The difference is jitter. This is the variation in timing of the digital bits. There is the data and then there is the digital timing. This is different than the music tempo. This is at very high frequencies, beyond audibility. There are no bit-errors except maybe on a severely scratched disk on the CD transport.

 

So why is this audible? It is audible because the variation in timing jitter modulates the digital waveform in the audio band. This wreaks havoc with the D/A converter so it outputs a lot of distortion components that are not in the music file.

 

How to get rid of the jitter on a SB3?

 

One solution is the Empirical Audio Pace-Car reclocker. One version of this is designed expressly for the SB3. A clock input is added to the SB3 (a very simple mod). Then the Pace-Car's internal low-jitter clock drives the SB3. The data from the SB3 is put into a FIFO memory and then clocked out with ultra-low jitter. The output from the Pace-Car can be S/PDIF coax, AES/EBU or I2S depending on what your DAC needs. The I2S is the highest performance followed by the AES and S/PDIF.

 

The second problem is choosing an excellent DAC. There is NO reason why a good DAC will not outperform your integrated CD player. You just need a good one. I can recommend a modded DAC, the Northstar 192 (stock with I2S input) or the Benchmark DAC-1. These can both be purchased used on Audiogon. I dont listen to any stock DAC's. They are just not good enough.

 

Steve N.

Empirical Audio

http://www.empiricalaudio.com

 

 

[The Computer Audiophile]

Thanks for the detailed information Steve.

 

[audiozorro]

Let’s get back to basics especially since you don’t want to spend money on anything without having some confidence that what you purchase will be any better than what you have. Your reference seems to be your Rega Apollo CD player, which for the sake of simplicity is just a CD transport and internal DAC. You fail to mention if you find the sound quality of the standalone Rega player to be better than the Rega player connected to the Mark Levinson DAC. If you do, then I say you need a better DAC if you want better sound quality. The Rega Apollo is a decent player but there is nothing exceptional about its transport or internal DAC.

 

You also fail to mention what PC software you're using for FLAC compression and what the software settings are. Things may be somewhat more difficult with Windows PCs but there is no reason for you not to get excellent results.

 

The Squeezebox is a very affordable and convenient device just like I can say the iPod is a very affordable, convenient and portable player. Neither device offers sound quality that cannot be bettered for a reasonable cost. Alternatives to the SB include the Transporter from the same manufacturer or just using a much better DAC with the SB.

 

Wireless or 80 foot Cat cables provide convenience but they also diminish high quality sound.

 

I don’t know why you would say the SB3’s internal DAC seems to handle the jitter reasonably well without the elaborate jitter suppression scheme of the ML DAC. Jitter is a problem, though it's not your only problem, and you are obviously not satisfied with the music quality from the SB3 as compared to your Rega player or the DVD transport/ML DAC.

 

 

[The Computer Audiophile]

Hey guys - let me soften the tone a little bit on this one :-)

 

What do you think of the sound quality of the Rega v. the Rega / ML combo? The Rega has a lot of fans, and for good reason, but there is some room to move up.

 

What software are you using to compress FLAC files? You may want to adjust some settings which many people around here can discuss with you. Who knows maybe you've been down that path already.

 

It's somewhat interesting that you find the SB3's internal DAC handles jitter pretty well. In my experience I've come to the opposite conclusion, but if it sounds good to you then it's good.

 

[audioengr]

There is no reason why networked data streams will intrinsically affect the sound, either wired ethernet or WiFi. These are packet-based protocols, so jitter is a non-issue. It's at the end device that converts the networked packets into a stream of S/PDIF data where the jitter comes into play. This is the SB3 itself.

 

Steve N.

Empirical Audio

 

[rom661]

I really don't have a lot to contribute on this one except for a little context. I am very familiar with the Mark Levinson 36, 36S, 360, 360S, and 30.6. They were all good products in their day, some of them reference quality. However the No. 36 is simply not competitive with a well executed current design. The 360S and 30.6 were excellent in their day but can be bettered by a good DAC today for a fraction of the cost.

 

Please understand that I don't say this to take a shot at your Levinson piece - I have owned about half of the models I listed including the 30.6. I mean it in a more positive way. Give a good quality modern DAC, which are fortunately being designed and manufactured again, a good, low jitter signal and I think you will easily outperform both the Levinson and your current CD player. I just had a No. 36 in for service a few weeks ago and it really made me realize how far things have come.

 

Beyond that, there are lots of people who can give you great advice on the forum, I just wanted to encourage you in your quest.

 

Best wishes

 

Rick

 

[duke43j]

Hi everyone. I didn’t realize I would get such an enthusiastic response. That’s great! Thanks for the help.

 

Unfortunately, my Rega Apollo doesn’t have a digital output, so I couldn’t feed it to the ML DAC for comparison. I did connect a 5 year old el-cheapo DVD player to the ML DAC and it sounded better than the SB3 – ML DAC combo, but not as good as the analog out of my Rega. The DVD – ML DAC sounded thinner in the mid range and upper bass than the Rega, although the bass did seem quicker with the ML. Maybe it’s more a matter of preference, but I liked the warmer, richer sound of the Rega. The SB3 – ML DAC was definitely a step down. The instruments didn’t pop out at me; they seemed one dimensional. The notes seemed to decay faster; they didn’t “ring” as much. I was not happy with the sound.

 

I used Exact Audio Copy to rip the CDs to FLAC files. I don’t know much about the software settings, but it seemed to work OK. I noticed that I did get some errors on some of the tracks (e.g. 99.9% correct). I don’t know if this is normal or not.

 

I agree with Steve that the data packets shouldn’t have an effect on sound quality. If there is a problem with the data transfer I would think it would show up as dropouts or skips, not tonality. It’s the jitter going into the actual D/A chip that needs to be regulated precisely. I was under the assumption that any decent DAC would reclock the input to virtually eliminate jitter problems. But, based on Rick’s comments, maybe that is not a good assumption. The only experience I have with outboard DACs is the Mark Levinson 36s that I had for a couple of days. Do you think I would see better results with a more modern DAC? Or, am I going in the wrong direction entirely with the SB3?

 

Incidentally, my system consists of

Rega Apollo CD player --> VTL 2.5 preamp --> Classe’ CA-100 100 W/Chan Amp --> Thiel CS 2.4 speakers

 

 

 

 

[rom661]

I think you would be very pleasantly surprised if you went to a server based source with a USB DAC. I am a fairly recent convert to this way of doing things but I believe it is the future in terms of ease of use, sound quality, and value. After I saw your response listing your equipment I set up a system using a MacBook, Benchmark USB DAC, a VTL 2.5 pre, the newer Classe CA-2100 power amp and Thiel 2.4's. Obviously there is a lot of overlap between your system and some of what we carry in the store. I don't cary the Rega but I have heard it and consider it a competent player for its price point. I compared the server based system to a couple of different CD players, including Musical Fidelity, Rotel, and the entry level Classe. I preferred the server/DAC to everything except the Classe, which is a $4500.00 player. I have no knowledge of the SB3 at all but I can tell you that I got really nice sound using the above front end.

 

My best suggestion would be not to rule out a DAC solution based on your experience with the 36S. The design is about 15 years old and is no longer competitive.

 

I hope that helps a little.

 

[duke43j]

Wow! I can’t believe you went to the trouble of duplicating my system to evaluate the sound. You guys are amazing.

 

So, it looks like the Mark Levinson did NOT adequately eliminate the jitter. That is surprising since it was a $6K unit when it was new, and I think it uses an oven controlled clock. Maybe the unit I had deteriorated over the years, or maybe it’s just old technology.

 

Thanks Rick. I think my next step is to try a more modern DAC with the SB3. If that still doesn’t work, then I need to step up to a Mac server.

 

Thanks again for the help.

 

 

[Al]

...I do'nt tend to worry about individual tracks being less than 100%, as long as the eror report says there were no errors. I also know people with better systems than mine who follow the same principle.

 

Naturally, tho, opinions may differ.

 

[rom661]

In fairness, its not like I went out and got all that gear - we just happed to be dealers for a lot of it. Getting good digital sound is about more than low jitter. The quality of the analog section of the DAC is very important as well. Power supplies count, etc. I have no direct experience with the squeezebox but have heard a lot of comments about how cool and fun to use it is, usually followed up by a caveat about not being a candidate for a great sounding system. I made the comment about the 36 to show that DAC's have come a long ways, but I would guess that the Squeezebox is more limiting than the No. 36 was. Maybe you could borrow a Mac from someone and properly rip a disk or two to it, then run it into a respectable USB DAC. I think you would be impressed.

 

Keep at it. These guys helped me past a "knows enough to be dangerous" phase on the computer side of things to where I now feel qualified to advise our customers on their options on straight forward applications.