Apox digital X-over

[netgeek]

I'm actually a big fan of op-amps and planned to use lots of them in an active crossover... The devices are so good these days that I'm sure I personally can't hear anything they might contribute - but others may disagree. However, I'm thinking that something like the TAS3103 might be worth trying as an alternate (because A/D and D/As are also pretty good these days ).

If you take a look at the excellent work done by Linkwitz (specifically his active design for the Orion, et al) he has obviously done an amazing amount of testing, tweeking and optimising. He's also explained it all very well and if you take it a section at a time it's perfectly logical and clear.

With a device like the TAS3103 you can implement the same functional blocks (ala Linkwitz) with the added advantage that you can very quickly make changes (e.g. throw in a notch filter at the last minute if needed) based on your test results. What's more, you can also add delay, amplitude compensation curves, etc., etc. - all without touching a soldering iron. Instead, you merely update the parameter table to be loaded into the TAS3103 to reflect your changes and you're done (at least until you change your mind again )...

So, the question for me at least is what it sounds like and whether or not it's worth the trouble. I'm thinking it may well be worth it although Dan has pointed out above that the tools are fairly "clumsy". The prospect of a single A/D --> TAS3103 --> 3 D/A solution (all fairly cheap!) looks attractive if it plays out as well in reality as it does on paper.

Just my 0.02..........................

Bill

"So, is the universe really analog - or digital-with-infinite-resolution ?"

[dmfraser]

Our listening tests does put this device in the audiophile class. The total THD+N, input to output on the DSP I made with the TAS3101 is in the area of 0.012%. Running at 96KHz and 24 bits. Used good AKM A/D and D/A converters with 110db+ dynamic range. For opamps on the output filters, I used OP275s. The input and output on my DSP is fully balanced as it is for pro use.

If anyone is trying this device and wants some help, using my experience, write me at dmfraser@sbcglobal.net.

If you write a better GUI for it, contact me too.

[WTS]

I personally don't like opamps, from what I've heard of them in the past. Granted, I have not heard any of the lastest super opamps. I just think the less active circuitry in the path the better. I once built a 3 way active xover(i don't recall off hand what I was using for opamps). I thought it sounded great until I decided to try your basic 6db xovers at the front end of each amp. A world of difference, it just opened up. So what was at fault, the design as a whole, the opamps used, I don't know. But I know of other people who went the same route and they won't go back. But thats just my 2 cents worth.
Now as far as doing it in the digital domain, I'm sure that comes with its own pros and cons. I think I'd rather do it the digital domain. My system now is strictly digital right up to the pwramps(biamp) so it would be kinda hard to implement an active analog based xover.
dmfraser,I'm glad to hear that the TAS3101 rates right up there. There seems to be alot of talk about behringer units, do you think this one could surpase it or equal it.

[dmfraser]

Behringer stuff is decent but not super. They make compromises to get the price so low. More bar band equipment than real [ro.

[niconoise]

has anyone looked at the ad1954?

[netgeek]

The Analog Devices widgets look very interesting but according to their data sheet "max 48 kHz sample rate".........

Also, they have alot of extraneous features and options which seem geared more towards car audio or lower end 2.1 applications. Still, they're on the right track...sort of......

Regards,

Bill

[dmfraser]

I found that with a 48KHz sample rate the THD+N is about 3 times higher. On the same test unit I get 0.048% THD+N at 48KHz and 0.016% at 96 KHz.

This translates into a somewhat grittier sound at 48KHz though the extra THD does make to sound seem a little brighter. Adding some dither helps with the distortion at a cost of more noise. I have to design for 100db of more S/N so I have to do 96 KHz. However, for consumer use, where the sound source is 16 bit consumer grade CDs sampling at 44.1 KHz, playing through low powered (under 200W) low efficiency speakers (<95 db 1W/1M) then 48KHz is likely OK. Its just not audiophile.

I'm using, from AKM, the AKM5385A A/D and the AKM4395 D/A. I also use the Cirrus CS4362 in some products. All these are balanced input/output devices as I cannot get over 90db S/N or dynamic range out of single ended devices when I have 1000W Class-D power amplifiers as part of the system.

By going fully balanced and running at 96 KHz, I can get up to 107db dynamic range from the system.

Dan

[netgeek]

Well, since it's been a month now since the last post - we must all have had a chance to think about it, right?..........

I'd still be interested in the TAS3103 or AD1953/4 approach but can't bring myself to hand over $700 or so for an eval board just to play with either device. The alternative would be to glean as much as possible from the published app notes and then lash together a preliminary design to hack at but, unfortunately, the quantity of material available (e.g. not even a published reference design ??!) seems pretty sparse.

Dan, if you have an eval board - did they provide much in the way of support materials with it, or do you pretty much have to wing it from scratch?

Bill

[dmfraser]

TI included a GUI with the TAS3004 and TAS3103 eval boards I bought. They also included a piece of software called the Automatic Loudspeaker Equalizer where you import MLSSA data and it will automatically come up with a set of EQs for you to make your speaker match the curve you give it. They are asking $500.00 for that by itself though I don't know if anyone will pay that.

As well, when I found a feature on the GUI was not operative, I complained to TI and they made the feature operative and sent me a new version of the software. However, it is likely what they are shipping to others is sill unable to write to an EAROM for storing setups.

The DSP eval board for the TAS3103 was fixed at a 48 KHz sample rate and I had to change the crystal to make it run at 96K. As well, the A/D and D/A on the eval boards were only consumer grade and I had to use the I2C inputs and outputs on the EVM to go through decent converters.

However, I was able to get a functioning DSP built without having to write any code for it. And I got over 100db S/N out of it.

I just got my prototype PCBs today for a 1 In/3 or 4 out DSP using the TAS3103 and I hope this will work as good as the 1 in/2 out did for me.

Dan

[netgeek]

It sounds like the support stuff TI provides is at least somewhat useful but I suspect that if I try the "lone hacker" approach (i.e. without eval board, etc.) I probably won't get too far. And without a "real" (that is - "commercial") application and an equivalent "real" customer I can't realistically expect much help from TI... Can't fault them for that really - they need to filter out the "tirekickers" (like ME ) from live customers after all. Unfortunately, since I don't have my old day-job to use as a cover story.. .. I can't just get in touch with TI's product manager and ask for any favors.

Anybody want to rent out an eval board?............