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Gordon/Folks:For stereo, what is that maximum throughput for USB2.0? Can we do 24/96? 24/192?
Now - let's say we *can* run three USB devices for a tri-amp setup. What is the maximum throughput for *all three*? Is it the same as one individual connection - since USB connections share bandwith (is that correct?)
Anyone have any hard numbers?
Follow Ups:
Presto,Yes the speed estimates Thomas states are true.
The problem is that ISO data is only supported to 24/96. There is allot of bickering for a new USB Audio spec the problem is that the gammers, video people, home theater and 2 channel guys all want something different.
There are some companies who wrote their own drivers and have custom solutions for this and with theirs the 480MB limit is possible using USB.
The only true silicon solution available today for what you want is using the Oxford Firewire chipset. It has 8 possible channels with 24 bit data. Problem is the chip has real jitter issues. Of course those can be taken care of externally if you specified specific speeds and data rates you could add PLL/VCXO's to fix it's problem. It would not be cheap though.
I guess the first question would be... what's TRI amped and what computer program are you using to generate it or support it?
Gordon:Active multi-amping is when you use active crossovers and run a separate amp for each channel "pole", for example, bi-amping would require two stereo amps - one for low-pass (LF pole) and one for high-pass (HF pole).
For active triamping I am using DSP based crossovers. Some are for Foobar only, and one other (my favorite one) is a VST plugin that works with DSP based mixer/sequences, or ASIO drivers/mixers that have DSP mixing capabilities. You might find it interesting:
www.thuneau.com
There are a number different ways to get the audio out to the amps when using the PC for DSP crossover functions:
1) Use a multichannel PCI soundcard analog outputs (Lynx 2B, etc)
2) Use a multichannel PCI soundcard digital outputs (Lynx AES 16, etc)
3) Use multiple PCI soundcards for low/mid/hi SPDIF out (Chaintech AV710,etc).**
4) Use some sort of USB multichannel solution*
5) Use three stereo USB solutions**
6) Firewire solutions***
7) Proprietary data transfer solutions (E-Mu 1820M)* The prosumer USB solutions vary greatly as how they go about transfering data and which USB chipset they use to do this.
** Not all stereo solutions will support multiple instances for multi-amping. Custom drivers may need to be written. Sometimes all one needs to do is customize the driver .ini file so that the three (identical) soundcards show up as distinct devices.
*** The jitter issues with many Firewire interfaces are well known.I like the idea of USB because of isochronous transfers and reclocking the data at the receiving end. Either that, or high-buck professional SPDIF or AES solution where the clock source can controlled, and everything can be slaved to a single (high-quality) clock source. It's do-able but not cheap. I could buy a Mac and save myself the headaches for that kind of money! ;)
Going SPDIF (Async/PLL) does work, but it's just not the best possible solution in all cases. I've heard some good results with the Cirrus Logic CS8420 (in the Behringer DCX/DEQ2496 units) but their output stage quality is not high enough to hear the low level detail where the soul of the music resides. It's clean with a very nice black background, but it's just not quite "there".
USB is still new tech, and *most* consumer stuff only does 16/44.1 and 16/48. Apparently only custom USB solutions (such as yours) with custom drivers do higher bitdepth/samplerates. The *good* USB dacs (like yours) are not mass produces and do not come cheap. It would be a lot of loot to shell out for three *good* USB dacs to do tri-amping (assuming multiple instances can work). For that money, I could go the Lynx AES16 route and get three Ack Dacs or Benchmark DAC1's.
Then I either need to get a sixchannel preamp (either high-end HT receiver or custom high-buck unit) or just go with passive attenuators.
I am a propeller head. I like to complicate things.
Truth be told, I'm just addicted to active multi-amping.
Presto,Sorry I got the impression you where doing like a 3 channel not 3 way system.
I am not at all a fan of this as you have read my thesis and rambling on other forums. The gist of my thesis is that between 100-10k all the amplifiers need to be the same or the dissimilarites in sound between the amplifiers clouds the over cohesion of the sound.
Anyway... other thoughts...
The Crystal CS8420 is evil... ask anyone. Play Linda Ronstandt's first CD (original one not the remix) and the CS8420 freaks out.
Passive preamps suck the life out of everything. Especially TVC's they don't have the inductance required for low end and phase shift like crazy.
Your best bet would be the Oxford part. Sorry... I developed a nice dac for someone else with 8 channels they stole the unit and never paid me. I don't have the time to do another design like that but maybe someone else does. The Oxford needs a secondary PLL/VCXO because the clock out has something like 10ns of jitter.
Anyways... my thought would be dump the whole triamping and go with a really good 2 channel. It will cost 1/3 the amount, have 300% less headaches and will sound better.
GR: "The gist of my thesis is that between 100-10k all the amplifiers need to be the same or the dissimilarites in sound between the amplifiers clouds the over cohesion of the sound."Absolutely, without question, correct! :o) Also, identical amps makes gain matching a breeze.
GR: "Passive preamps suck the life out of everything. Especially TVC's they don't have the inductance required for low end and phase shift like crazy."
Thanks for THAT information...
GR: "Your best bet would be the Oxford part. Sorry... I developed a nice dac for someone else with 8 channels they stole the unit and never paid me."
That really sucks. Send me their address and I'll recover the unit and then buy it from you! Just don't ask about the repo details. ;)
GR: "Anyways... my thought would be dump the whole triamping and go with a really good 2 channel. It will cost 1/3 the amount, have 300% less headaches and will sound better."
Hey - if all I wanted to do is drive a single set of really good speakers I would have already bought your 2-channel USB DAC. But I have all these "components" and boxes and speakers in sort of a "propeller head" speaker lab type environment and I am constantly changing active speakers and coming up with new crossover algorithms. I have worked on over a dozen iterations in the past year alone. This is why I love active so much. Some DSP crossovers I have do up to 7th order IIR filters with phase correction. Others are FIR based (linear phase) with slopes up to 800db/octave (!), and are transient perfect as well. Others are IIR based and do traditional filters and sound quite nice as well despite not being transient perfect. All crossovers have very valuable individual channel delays and level controls to prevent bad effect of over-runs. 2 of the DSP crossovers I have (Aedio FIR and Thuneau Allocator) even do on the fly re-calculation of filter taps based on input sample rate. Very valuable attribute indeed!
One day I might go USB 2-channel into my nice CR Developments Romulus Integrated into a "helluvagood" pair of speakers. But I'm just having too much fun with the "300% more headaches!" :o)
Did I not mention that I was a *mad* speaker scientist?? :o)
Thanks for the thorough response. But for me, PC Audio is not about finding 1 good solution (you already DID that...) it's about finding many different solutions using a vast variety of approaches and having much fun and learning a lot in the process.
USB has nominal 480Mbit/s. Assume you get 30% actual throughput.Stereo 16/44.1 ~ 1.5 Mbit
Stereo 24/96 ~ 5 Mbit/s
Stereo 24/192 ~ 10Mbit/sThis leaves you with enough bandwidth to handle approx 15 stereo pairs at 24/192.
Even entry level USB2 soundcards like the Audigy 2NX handle 7.1 channels at 24/96 plus simultaneous stereo recording at the same resolution.
Higher end boxes like the Motu 828mkII with USB2 interface support
20 channels of input and 22 channels of output concurrently at 24/96.Cheers
The Edirol UA-101 is a multi-channel USB2 A/D-D/A converter and has a driver for Windows and Mac as well. Works very well.
nt
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