Tact question

Andy - regarding phase response: there's one thing you can do with TacT. You can select some very unprobable listening position where everything sounds completely out of focus, say at the side wall, where you can hear mostly one speaker. Then measure the freq (and phase) response for this position, create a graph, put a friend there, let him listen for a while, and when he is about to say what he thinks, press the button, and - voila - it all suddenly snaps into focus (for him - and goes out of focus for you). He'll be impressed, believe me. How about that for a phase change? ) Now show me a bass trap able to do it ))

 

Ahhh.. you found the balance control

 

Tenson, whose balance control works in the time domain?

 

That's the only thing I missed when I sold my Bryston preamp


Made another efford (just for fun) to "TacT" my Shahinians. The thing is - Shahinians freq. responce is purposely screwed. Just flattening it out ruins everything - they start sounding awful. "Improving" on what Dick Shahinian have done tuning them by ear - well, it's a big mountan to climb

 

Nomoretweaks, mine, but AFAIK not yours

 

Didn't you say it still helped the bass though?

 

The room correction facilities are still naff, completely unusable IMO - you need to mess around sending measurement files off to DEQX and they give you these correction files back, I tried it and thought it sounded worse! The speaker correction is good on it though and I can't fault that. For room correction I've grown very fond of a clever little program called DRC which creates a modified impulse response which is then applied through a convolver. The only real downside to this is you need a really top flight mic to capture the initial impluse. I gave up trying to use the Behringer ECM8000 and rented an Earthworks M51 and matching mic-pre for a couple of weeks. Another which some see as a downside is using a PC for source duties. Not a problem with the pro audio soundcards from the likes of creamware, Apogee, EMU, Lynx, Digi and RME. As far as digital goes these boys are at the top. If your an analogue fan then clearly a PC is *the* antichrist though.

A word of warning though, DRC needs a fair amount of understanding to fully harness, it does come with some presets that are simplistically named mild, average, strong etc. and these simply set the level of blind brute force applied to the correction. Non worked particularly well with my room. Luckily the author of DRC includes a rather hefty .pdf which helps to fully configure every aspect of the correction filter and also helps to identify where the variables should be applied through reading the data contained in your initial room measurements. All that's required here is a little time to understand rather than an IQ of 170, so don't be put off.

Once I'd dialed DRC in, I couldn't believe the difference between having it on and having just simple upper frequency correction in the form of 2" foam treatments on the walls. Night and day stuff here, not subtle at all. Good DRC imparts a sense of absolute coherence from top to bottom and in all aspects of the sound. Easy to get wrong and tough to get the best from it, a little time and its impressive stuff though.

I think the primary reason why the Tact and DEQX suck so badly at room correction is the fact they aren't particularly configurable and the simply don't have the DSP horsepower to enable accurate and transparent correction - the PC does luckily.

 

High end sharc chips have much more horsepower than any PC when it comes to dsp so it should be possible for a high end audio outfit to produce a unit that can.

 

Perhaps not cost efficient though when a high spec laptop will do the job?

Have you had a chance for a proper listen now?

 

You'd think so but that's not the case at all.

Put it this way:

I had 6 channels of studio mastering plugin; Waves Linear EQ for FIR filters and speaker correction along with time alignment delays - these 6 channels formed the basis of my 3-way crossover for the fronts. THEN add in 6 channels of speaker specific DRC for 5.1 surround taken care of by Voxengo's 'Pristine Space' multichannel convolver.

All that was done by the PC and then the digital signal was farmed out to an Apogee DA16x DAC. This was when I had the PC XO setup, I've since moved on to the DEQX and whilst its reliable and really easy to use, it has only about a 10th of the power and flexibility of the PC setup. The DEQX has two 32bit SHARC dsp's and it can only just manage to do the FIR filtering and correction for a pair of 3-ways. Looking at the DSP usage meter shows I'm running the DEQX ragged.

If the PC was 100% reliable with low latency then I'd drop the DEQX in a heartbeat and go back.

Perhaps controversially, the PC sounded better too when it worked OK. Like I've said before, I use DRC on the PC for erm DRC because the DEQX is so poor in comparison so for now I've got a hybrid solution that works well. I'm going to be reinvestigating the PC XO setup in the very near future as I've just bought some new kit, including a swift Intel conroe running at 3.4Ghz(overclocked) that should really let the solution shine.

 

Ant, when Nick talks about the high end Sharc processors, they are very different from the low end ones used in the likes of the Behringer and the DEQX.... but they cost more than the DEQX just for the processor I think!

 

Yes indeed - the sharcs I am talking about no PC could possibly compete with. PCs have a general architecture whereas high end sharcs (which might cost over $1K per chip) are specialised just for dsp. They also lend themselves to paralelisation in a way PC chips dont. You can also on-chip compile with FPGA arrays and optimise for a specific dsp task but thats a different story.

I used to work for the miltary in a department that did a lot of dsp research. For ultimate DSP they use top end sharcs. Using a pc chip would be ridiculed as woefully inadequate. The sharcs in the behringer are jellybeans chips.

 

So my original assessment of saying the PC owns the naff stuff they put in the DEQX, Tact, DCX and virtually every surround sound decoding amplifier was indeed correct

As far as the DSP your talking about are concerned, they don't exist for us here. No commercial audio equipment uses them and certainly nothing that's aimed at DRC and FIR filtering intended for loudspeaker usage. Maybe in another 5 years time that will be different. For now a multi processor PC is top dog regarding audio processing for the home and studio, which was my original point.

Maybe someone will come up with a PGA that has enough power and flexibility

I believe that the latest generation of FPGA's and CPLD's will take a strong foot hold, dCS has been using these for years now with great sucess. We already see the competant Xilinx used in pro audio products for routing and processing of signals with zero latency and overhead. They're also extremely adaptable.

 

I made no comment disputing that - I stated that high end sharc chips could easily do it - and they could be included in high end kit. It is you that then disputed my comment about high end sharcs being bfaster than pcs These sharc chips would still be cheaper than a pc.

 

That's because we were talking real world stuff, available now, or so I thought. I considered that you meant the fluff used in the DEQX and Tact was actually more powerful than the PC stuff. Had I realised you were talking about a fictitious product based on a specialized part then I would have agreed

What, even after you've paid for the rest of what goes into a commercial product? If the baseline DEQX is £2k now I have no problems believing that would double with these more powerful DSP.

A decent PC with the horsepower required for full DRC and filtering functions over multichannel audio and multiway speakers would cost around £1k depending on how extravagent you went. Then add in a sound interface which frankly will cost anywhere from £200 to £4k+.

For a decent starter PC XO setup your looking at £2k.

 

The deq is £200 isnt it?

No I was discussing what was hypothetically possible - I did say high end sharc chips.

Even a pc would struggle to do all of the really advanced dsp that is possible for dvd-a in real time. Too many latencies and not enough horse power. Peak to sustained computing ratio is appalling for intel - maybe 20% in real life. Plus you need many cycles to do one dsp operation. Just pick a sharc that gives you the same product price point as the pc you are aiming for and you will likely have an order of magnitude more DSP power for those fancy algorithms. In a similair fashion to PC graphics cards. I suspect the reason people havent done it is they just stick with vanilla DSP so it makes sense to use cheap sharc chips rather than intel, more powerful sharcs arent required. You could always stick a sharc card in a bare bones pc though. One of those cheaps ones for industrial control. I bet that would be a good solution.

 

DEQX

DEQ2496

 

The basic DEQX is £2k, although its possible to spend upto £8k for a tricked out one from places like Overkill.

I've played around with a couple of the common solutions; DEQX and Behringer DCX. These aren't approaching the PC for processing power. I mentioned above about running a 5.1 setup with a 3-way FIR filters for the fronts, along with delays and 6 channels of discrete DRC not to mention simultaneously decoding a DD or DTS bitstream and playing back DVD's or Hidef(not H.264!), all this with no dropped frames and no audio stutter. Everything else out their is a joke in comparison.

You should check out the current state of the art in filtering software on a highend PC with a studio quality sound interface. ASIO/WDM/DX platforms are geared for low latency, sync and bit perfect playback.
Waves are a good outfit that traditionally supply studio mastering plugins that are used for shaping and creating the music we all enjoy so much. Not particularly cheap at around £800 for the suite of Linear Phase plugins but the quality is beautiful.

I spent good money on my Overkill modded DEQX and wouldn't hesitate to drop it in favour of the PC *if* I was guaranteed stability. The PC is just plain better in all regards except ease of use and reliability.

DVD-A is trivial stuff for a decent PC. I wasn't impressed though as it was based around the poor WinDVD software.

 

What are the DEQX prices and where to buy ?

I assume that this is the sort of thing to go for if you find the Behringer DEQ2496 usefull but want better quality ? or is Tact the better option ?

 

Neither the DEQX nor Tact are particular good at DRC. People will tell you they are but don't believe it, they're not. The DEQX is good for speaker correction and crossover duties though. The Tact doesn't offer the flexibility of the DEQX even with the add ons, so overall I'd say its expensive product with little appeal.

You can buy the DEQX from either the manufacturer in Australia, Overkill Audio(expensive modded version) or Tekcare here in the UK:

http://www.tekcare.co.uk/Scripts/prodList.asp?idCategory=1235

My first DEQX I bought from Tekcare and I can highly recommend them. Very helpful and speedy delivery