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]

Absolutely...

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]

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]

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.

 

[OzMikeH]

I've started playing with the Itunes EQ.
what settings do you suggest to start with for a baffle width of 10.5 inches, the driver is equidistant from the top and sides so I think I should give it a steeper slope than normal.
Ceiling height is 105 inches.

A practical example such as this will help others work out their own starting points.


Bob, I've found EAC good for damaged CDs. Since getting a Mac mini I only use EAC for the damaged ones. Itunes is pretty good as long as you check the error correction box.

 

[nesha]

Anybody tried Musiland LILO usb dac? 99 bucks from Pacific valve&Electriic Company, and with promising dsp capabilities.

 

[OzMikeH]

I suggest you repost in Digital forum after searching.
That is assuming your post does not relate to fullrange or widerange driver correction with DSP. If it does I apologise, but please elaborate further.

 

[nesha]

Welll, I m snooping around possibillity ti get away with just one biiiiiiig
fullranger (like Audio Nirvana super12cf, or Monacor fr 12) in OB . DSP seems a i must . Pass f1 or f2 would be nice but i m not sure these amps would give enough bass boost for OB?

 

[ilewis33]

Hi, I just finished a rough pair of BIBs for a pair of Fostex FE126es. I'm powering them with an original T-Amp, and running my MacBook as a front-end. My plan was to then start on a pair of frugelhorns or possibly Saburos as time permitted. However, prompted by this thread, I opened that equalizer window on iTunes and started moving sliders.

Result: I doubt I will bother building anything else! With a few tweaks you can get rid of the Fostex shout, compensate for baffle step, and bump up the bass response (within reason). I also bumped up the 16K a little bit to add some sparkle (thereby saving me money on a supertweeter!).

Since BSC correction filters, wire tweaks, suprabaffles, speaker basket damping, etc, are all frequency response modifiers, why not just do things directly? That way, you're not losing any efficiency, and you can play to your heart's content.

I'm very pleased, and thank you for this thread. I'm sold on full-range + eq. (Parts Express sells an AudioSource EQ for $119, in case anyone wants to play with this concept without the benefit of a computer source).

 

[Scottmoose]

If it's an original, unmodified SI T-amp, you might want to modify it as the response is deliberately rolled off drastically below ~100Hz

 

[OzMikeH]

I agree up to a point, basket damping is more about killing resonances and stiffening.

I've been playing with Itunes EQ for hours. I have a Mac Mini -> Edirol UA-1EX -> 6 inch interconnects -> PP el34 -> Fe207E + FT17H in Singulars.

I've snipped 0.1uF out of my tweeter caps, now running 8 ohms plus 0.47uF for an XO point about 21kHz.

32Hz on zero, 64Hz and 16k -1dB and everything else -2dB.
My DAC clips with any bass boost at all.
Acoustic seems to have better microdynamics with no eq, that could be my imagination.

It'd be nice if Itunes could upsample to 24 bit prior to the EQ, twice as many sliders would be good too.

 

[ilewis33]

Thanks for the note about the T-Amp bass response. I found a graph here:

http://www.michael.mardis.com/sonic/measure/5066-freq.html

Looks like a very smooth roll-off starting at 100 Hz. I'm looking at the various modifications that can be done, but I may just spring for one of the later generation T-Amps (or 41Hz kits) that doesn't suffer from the problem, and continue to compensate for the rolloff in eq in the meantime.

I'm still running the amp off the 8 AA's, so I have plenty of room for improvement!

About the basket damping - I had read about it being a partial cure for "forwardness" and "shout" and so assumed that it was somehow intended to curb the peakiness of the driver. But I guess there are other reasons to do it beyond peak taming.

I agree about the number of sliders in iTunes - I have been looking for a plug-in, but have mostly found the "sonic expander" sorts of things, rather than just an improved graphic eq.

 

[pjanda1]

Computer digital front ends are the only way to go, in my mind. I haven't done it yet, but I'm sure not going to spend any more on disc players. I would love to be able to adjust my BIB's cabinet gain in the digital domain rather than with polyfill (about 10 lbs in 'em right now). And it would be great to use as BSC for my non BIB cabinets. The only problem is that I've recently been working on a nice vinyl set up, and I really like it. I'd hate to have to run it through an A/D converter.

A couple of years ago I heard an demo of a digital response/phase correction system marketed by AV123 (now replaced by software products for their dac). I asked Mark Shifter (AV123 pres) about building speakers to be used with the correction system, rather than the other way around. He didn't quite get it, and gave me an answer about such things not allowing one to get away with bad speakers. It seems to me though, that all the frequency shaping done in crossovers (BSC, notch filters etc) would best be accomplished in the digital domain, not passively. I hope manufacturers will someday embrace this possibility. I don't see it on their site now, but NHT had a well reviewed 3 piece active system designed this way.

pj

 

[Leglandu]

Hi all, and thx for your thread Bob !

I own a FE168ES BIB and had some problems to get a nice sound, irregular curve of the BIB plus a bad room...

So, the computer was perfect to fix that. Mine has an XtremeMusic X-Fi soundcard with Foobar to play Flac files or WebRadios - some of them are good enough now.

The stereo output of the card has a very low impedance and go directly into the amp, it sounds very good.

To set the DSP, I run a pink noise on Foobar and modify in real-time the curve in Arta Software or AudioTester.

Or I can switch to the soundcard's EQ and run RoomEQWizard. But unfortunately the X-fi has just a 10 channels EQ vs 18 in Foobar…

I have several setups, i.e. one is for the “normal” place in the room and another one for a “proximity” listening (working at the computer) with the highs hard pushed, the bibs are on the sides of the desk and it is about 70° off axis

Now, the only problem of this kind of “internal” configuration is, when the hard disk is working a lot, you sometimes get some small “electronic noises” from the soundcard