DSP and the Single-Driver Speaker

[Bob Brines]

In case you haven't picked up from my other posts, I have gone to a computer front end. I use a reasonably powerful dual-core laptop with the music files loaded on a USB hard drive in either FLAC or WMA lossless. That hard drive is synchronized with a drive on another computer for redundancy. My player is Foobar2000. The computer output goes to a DIY Paradise "Monica" DAC and on to the amp-of-the-day.

Using a computer eliminates all of the data flow problems with CD drives. Everything is bits right up to the DAC. Your sound quality depends almost entirely on the DAC.

On to the DSP. Foobar2000 contains a half-octave equalizer. I am now using this equalizer instead of passive filters on my speakers. I've pulled the passive filters out of all of my speakers except the ones on the HT. The results are better than great. I am convinced that the sound is better than with passive filters. More open and involving.

As a first cut, I set the EQ to be the mirror image of the speaker FR plot plus some BSC. Then I play with the bands to get the sound I want. It take maybe 15 minutes to dial in a speaker. How do you want it? Bright? Warm? Thumpy? No problem. I have different setting for different genres. The only thing you have to watch is that you can easily get too much excursion at the bottom by over EQ'ing the bass.

Give this a try. Besides being able to get to any track on any CD is 15 seconds, the sound is very very good.

Bob

[ttan98]

A few comments:

1. How do you minimise jitter from the computer front end?

2. I mention a few times that using digital x-over is a viable option, you have shown to the case by using some sort of equalization in the front end and hence eliminating passive components.

3. I am trying to design passive x-over to prove for myself whether they are in fact superior or inferior to digital x-over.

4. I had tried foorbar2000 before and stopped half way because I didn't want to convert all my Cds to Flac or some compatible convertor. I will try comparing the sound again ie with CD player(I feed by CD player coaxial output directly into digital input of my digital x-over) since you have tried it.

Cheers.

[Scottmoose]

I'm not surprised you're finding it a good setup Bob. My mate Ed's running a stock Squeezebox with FLACs, and sound quality is as good as or better than most £1,500 CD players I've heard. None of the potential problems associated with passive circuitry in the signal path too, aside from the possible excursion issues in the LF. I'll be shifting to something similar myself this year, funds permitting. Well worth exploring.

[klykx]

Currently running two systems using:

Old Athlon PC: UD10 - super-t - ANS8 BAss reflex + cheap jamo sub (in the office)

dual core laptop: monica 2 + gainstage + charlize + fe 207e MLTLs (in the lounge)

Correct me if I'm wrong but I thought that bits are bits and jitter is irrelevant until you get to the DAC and then each bit is reclocked (NOS) or smoothed (oversampled)..or both so it stays that way doesn't it?

system 3 is under development but will be disk + USB out via UD-10 I2S to EQ to X-over/dac/preamp to poweramps to OBs (variation on an MJK/felixx 2x emi alpha15 in U + ex3 + ft17h per side).

Running ubuntu and xp too

[Bob Brines]

Originally posted by ttan98
A few comments:

1. How do you minimise jitter from the computer front end?

As pointed out above, jitter only become an issue when you reach the DAC. Personally, I think jitter is overrated as a problem. While my DAC does sound better than cheaper solutions, I must say that the headphone output from my laptop is the equal of a Sound Blaster USB modem and both produce pretty darn good sound.

2. I mention a few times that using digital x-over is a viable option, you have shown to the case by using some sort of equalization in the front end and hence eliminating passive components.

I'm rather new at this computer front end thing, but it seems to me that the current problem is finding a good interface between the computer and the amplifier(s). Cross-over plug-ins are available for Foobar2000 and I presume other players. The output is then SP/DIF to a 5.1 decoder, fronts going to the bass and rears to the tweeter. You can driver a 5.1 HT receiver directly or you can use a modem. The SB USB will also do this. "Quality" modems can get pricey.

3. I am trying to design passive x-over to prove for myself whether they are in fact superior or inferior to digital x-over.

Go for it. Report back.

4. I had tried foorbar2000 before and stopped half way because I didn't want to convert all my Cds to Flac or some compatible convertor. I will try comparing the sound again ie with CD player(I feed by CD player coaxial output directly into digital input of my digital x-over) since you have tried it.

I chose Foobar2000 specifically because it is the only free player that will properly catalog classical recordings, although the procedure is not straight forward. The Rivers player is reported to work for classical also, by I can't report.

The reason for going to FLAC is not for the compression, it is for the tagging. You could use WAV with cue sheets, but I found that overly cumbersome. WMA will not support the data necessary to tag classical, but is fine and my preference for everything else. Playing FLAC or lossless WMA is absolutely transparent.

CD's should be played through you computer disk drive. The computer will capture all of the bits and the only SQ issue is the DAC.

Bob

[Kensai]

Its good to hear that someone with a better understanding of what he's hearing than my own is coming to some of the same conclusions. Now we just need a way to implement appropriate DSP at the driver level of whatever device you're using (sound card, DAC, etc.) so that all sound is output with appropriate processing so we could pull as many passive components out of the analog chain as possible.

Kensai

[OzMikeH]

a BSC plugin for Foobar would be wonderful. It is incredible powerful but you can very easily stuff it all up.

I'm wary of too much digital processing, you can't filter digital without losing resolution.
The only way around it I can see is if you use some very smart software to upsample (and correctly predict how to smoothly fill the gaps) before filtering.

Volume control in the digital domain is a biggie. A compact disc has 16 bits to quantify the amplitude of a particular sample which is about 65000 possible values. Now if you have the digital volume down at 1/4 of the max level you now have only just over 16000 possible amplitudes. those amplitude values that were whole bits are now quarters of a bit, this is clearly impossible so they are rounded to the nearest whole bit.
Now think about what happens when you adjust your digital volume control to a bit more than a quarter, the way it reduces the alplitude starts looking quite unpleasant.
Not everything should be in the digital domain.

I suggest you look at exactaudiocopy for reading your CDs. Tagging digital music is a nightmare, Especially when the online databases have so many errors. If anyone has a good solusion I'd like to know.

[Bob Brines]

Originally posted by OzMikeH
a BSC plugin for Foobar would be wonderful. It is incredible powerful but you can very easily stuff it all up.

BSC is nothing more than equalization. For example, set 311Hz +1db, 220 +2 156+3 and everything to the left +4. You now have 4db of BSC starting at ~400Hz. You can save EQ setings and A/B your changes. Next try -4dB at 77 to kill the floor/ceiling mode. Try +4dB at 156 to take out floor bounce.

I'm wary of too much digital processing, you can't filter digital without losing resolution.
The only way around it I can see is if you use some very smart software to upsample (and correctly predict how to smoothly fill the gaps) before filtering.

Very true. You do have to be judicious about it. However, I find that most of the damage is more theoretical than practical. In any case, you play with the thing until you hear something strange.

Volume control in the digital domain is a biggie. A compact disc has 16 bits to quantify the amplitude of a particular sample which is about 65000 possible values. Now if you have the digital volume down at 1/4 of the max level you now have only just over 16000 possible amplitudes. those amplitude values that were whole bits are now quarters of a bit, this is clearly impossible so they are rounded to the nearest whole bit.
Now think about what happens when you adjust your digital volume control to a bit more than a quarter, the way it reduces the alplitude starts looking quite unpleasant.
Not everything should be in the digital domain.

Again true, but again the problem is more theoretical than practical. Extreme volume control within Foobar can definitely be heard, but if you set Foobar to max, Windows to max, and the amp to the loudest comfortable setting, adjusting the volume down within Foobar is pretty transparent down to half volume. Loudness contouring would help a lot.

I suggest you look at exactaudiocopy for reading your CDs. Tagging digital music is a nightmare, Especially when the online databases have so many errors. If anyone has a good solusion I'd like to know.

I have compared WAV files ripped with EAC then converted to FLAC with WMA lossless files ripped with WMP, and I can't tell the difference. Both WMP and Freedb seem to be OK most of the time for "world" music, Tagging classical ad offbeat stuff is indeed a pain. A lot of hand editing is required. The Foobar tag editor makes it at least managable.

Bob

[kmaier]

I also have some nice digital front ends... computer-driven, etc. I've used RME digital cards (AES/EBU) for many years with both Mytek and Apogee workstation converters.

Digital has all of it's own issues versus analogue but that's another story. I'm not a fan of mp3 in the least and won't use it for anything... not even an iPod. It also tends to increase the playback level resulting in digital clipping on much encoded material in addition to high-frequency detail loss.

I've also found that the optical digital output on my MacBook Pro also increases playback levels resulting in digital clipping... this is a bit odd and disturbing.... as it defeats the purpose of a digital output IMHO. Need to look into this more, but for now it's really a work machine (day job) not my audio workstation.

I rarely use a computer based media player but will use WaveLab for playback at times... I always use an external convertor for all CD/DVD playback using SPDIF... as my player doesn't have AES/EBU output. My current digital front end consists of a Mytek Stereo96 DAC driving a pair of Jensen transformers (balanced XLR to unbalanced RCA) to drive either my amplifiers directly or my preamp. Results are far better than the typical DAC chips integrated into any computer or CD/DVD units.

I also believe jitter is more of a problem than many think... quite a few articles exist around this topic.... here's one that talks about it in more detail:

http://www.digido.com/bob-katz/jitter.html

Regards, KM

[jdbon]

I agree that a software solution allows for more customization/experimentation. I use iTunes (OS X verion) instead of Foobar, and am often adjusting the equalizer. Sure a flat response is a more "pure" philosophy, but frankly I just adjust to what sounds good to my ears. That said, a built in auto EQ either for iTunes (or even perhaps at the system level) would be pretty cool. Just connect your microphone or place your laptop in your seating position, have it send a test tone through your speakers and let it adjust your eq for you.