# Will Thunderbolt audio interfaces allow lower latency than USB audio interfaces?



## EastWest Lurker (Jan 27, 2014)

First of all, let's all agree that in all likelihood "USB is fast enough" and _please_ not go down that road.

That said, according to benchmark tests I read, PCi-e audio interfaces (with good drivers) like my RME HDSPe-AIO, still provide the lowest latency. Presumably Thunderbolt, which really is PCI-e on a cable, will match it.


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## EastWest Lurker (Jan 28, 2014)

Wow, you guys had really strong feelings about this.


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## Daryl (Jan 28, 2014)

I would guess that as nobody is using Thunderbolt, so nobody has an informed opinion. :wink: 

D


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## EastWest Lurker (Jan 28, 2014)

Daryl @ Tue Jan 28 said:


> I would guess that as nobody is using Thunderbolt, so nobody has an informed opinion. :wink:
> 
> D



Since when does that stop people here? :twisted:


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## Daryl (Jan 28, 2014)

EastWest Lurker @ Tue Jan 28 said:


> Daryl @ Tue Jan 28 said:
> 
> 
> > I would guess that as nobody is using Thunderbolt, so nobody has an informed opinion. :wink:
> ...


 :lol: :lol: :lol: :lol: :lol: :lol: 

D


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## TGV (Jan 28, 2014)

Hi Jay, you want an opinion? Thunderbolt, in theory, could enable lower latency than USB. It's not to do with the maximum speed of the connection (they're both faster than required), but rather with the way the driver interacts with it (direct memory access). However, an audio interface is only as fast as the driver, so it's pretty hard to tell in advance.


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## rgames (Jan 28, 2014)

EastWest Lurker @ Tue Jan 28 said:


> Wow, you guys had really strong feelings about this.


Well, USB is fast enough but you didn't want your thread to go there. 

Latency used to be a problem but it's a religious debate these days. The virtual piano on your computer has a response time faster than a physical piano and yet generations of pianists have gotten by without a single complaint about latency.

If you want your virtual piano to behave more like a real piano then you should actually INCREASE the latency. Same for any other instrument you care to pick.

Doesn't that tell you something? Yes - it tells you exactly what you asked not to hear. Sorry about that...

rgames


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## Ryan (Jan 28, 2014)

I say as "dja" said to Ali G: USB 3 is enough for all men.







If you go for a RME USB3 you will have no problem


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## Nick Batzdorf (Jan 28, 2014)

First of all I truly don't care. 

But as other people have said in so many words, my understanding is that the relevant "bottleneck" is the buffer, not the bus leading into it.

The real question is what application you have the question in mind for. Tracking through any A/D/A conversion has *some* latency that can comb filter with the live sound if you're monitoring in headphones (even if you bypass the computer). That's on the order of at least a couple of mS depending on sampling rate.

Playing VIs through MIDI is different, of course - several times longer.

If it's really important to you, monitor through a damn analog mixer and save your money! Whatever current version of the Mackie 1202 they're selling would work very well in your set-up. You're not monitoring through $15K speakers, so you won't hear the microscopic difference in sound quality.


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## NYC Composer (Jan 29, 2014)

I'm using Thunderbolt, but also Cubase, which is going to be higher latency than you get because of the difference between Logic and Cubase's record/playback scheme. Also, I'm using it on a slave Mini exclusively with VEP at a varying 1-2 buffers, so, added latency. I will say TBolt kicks ass in terms of being able to play a lot of voices at a low Kontakt buffer.

None of which answers your question. Apparently I just love to type


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## NYC Composer (Jan 29, 2014)

Nick Batzdorf @ Tue Jan 28 said:


> If it's really important to you, monitor through a damn analog mixer and save your money! Whatever current version of the Mackie 1202 they're selling would work very well in your set-up. You're not monitoring through $15K speakers, so you won't hear the microscopic difference in sound quality.



I really needed to make my studio footprint tiny, so I sold my Mackie 1604 and bought a MOTU Ultralite Mk3 hybrid. I use the included software as a front end, and I'm happier because that comb filtering you describe drove me batzhit crazy.


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## EastWest Lurker (Jan 30, 2014)

Nick Batzdorf @ Tue Jan 28 said:


> Playing VIs through MIDI is different, of course - several times longer.



And _that_ is the latency I am concerned with. From my research it seems to be coming down to this:

1, Pcie- e has lower latency than USB 2, assuming equally good drivers for each. 

2. But USB 2 interfaces are fine with good drivers.

3. USB 3 interfaces can potentially deliver even lower latency, with good drivers.

4. Thunderbolt interfaces can _potentially_ deliver even lower latency than USB 3, with good drivers, equal to PCI-e.

So at the end of the day, the driver is the most critical issue, followed by the physical reliability of the hardware, followed by the protocol. Therefore, an RME "Thunderface" would be my dream choice, but they don't currently plan to do one.


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## NYC Composer (Jan 30, 2014)

Interface. Duh. I need to learn to read.


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## NYC Composer (Jan 30, 2014)

Isn't Apollo Thnderbolt?


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## EastWest Lurker (Jan 30, 2014)

NYC Composer @ Thu Jan 30 said:


> Isn't Apollo Thnderbolt?



Yes, for the Apollo Twin. The other Apollos use Firewire for connectivity and TB for DSP but a firmware update is promised to make them all TB for both.

My experiment with the original Apollo led me to believe however, that I could not use quite as low a buffer with my templates as I can with my RME (PCI-e) HDSPe-AIO.


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## wst3 (Jan 30, 2014)

At the risk of annoying many...

There are literally dozens of factors that play a role in the final latency of an audio path, but the source is not one of them. 

Playing a VI from MIDI has its own set of factors that affect latency, but they affect ONLY the latency from generation of the event (keyboard or sequencer) to sounding the noise - so to speak. This is potentially murky, so feel free to ask, and I'll elaborate.

It is important to differentiate, however, between latencies associated with the generation of the sound and latencies associated with the delivery of the sound.

Jay's question appears to target this later issue.

So what happens once we have a sound ready to deliver to our D/A converter?

1) the audio data is handed off to a driver.
2) the driver 'massages' the data so that it can be handed off to the hardware
3) the driver hands the data off to the D/A hardware
4) the D/A hardware converts the bits to an analog signal
5) the analog signal is then passed to the next stage, usually some kind of amplifier.

If we assume that all drivers are properly optimized then the issue becomes how quickly can the driver pass the data to the hardware?

And the short answer is that it no longer matters. The approximate data rates for a stereo audio signal (in the digital domain all audio signals occupy 2 channels - an oddity that probably stems from the early interfaces):
44.1 KHz/16 bit = 1.4 Mbit/sec (176 MB/s)
48 KHz/16 bit = 1.4 Mbit/sec (192 MB/s)
96 KHz/16 bit = 3.1 Mbit/sec (384 MB/s)
96 KHz/24 bit = 4.6 Mbit/sec (576 MB/s)

So ok, at a realistically high sample rate and word length we need about 5 Mbit/sec (rounding up, headroom for signaling, etc).

Let's look at the interfaces:

USB2 can transfer 480 Mbit/sec - about 104 such channel pairs in a perfect world.

USB3 can transfer about 5Gbit/sec - that's over 1000 channel pairs.

Firewire 400 can handle 87 channel pairs.

Firewire 800 can handle 174 channels pairs.

Thunderbolt - at 20 Gbit/sec can handle a whopping 4300 channel pairs... nuff said.

But it turns out that transfer rates are not playing much into latency. Since we already agreed that all drivers are optimized then what are the factors, and do we need to worry about them?

It comes down to polled vs DMA access, and just how many 'things' we need to do with the data, and unless you are writing your own driver (I'm working on some Ethernet drivers right now<G>) you just don't need to worry about it.

In theory Firewire and Thunderbolt should be able to deliver better performance, in terms of latency at least, solely because they use DMA. 

Besides the ridiculously fat pipe, Thunderbolt has the advantage of being a PCIe interface - and there are a lot of folks with a lot of experience optimizing PCI interfaces.

But for the "typical" user today I think any of these interfaces will be suitable. For a power user you might have to consider USB3 or Thunderbolt... might.

Not to make people's heads explode, but all of these interfaces are going to go away in the not too distant future. Everything will run over Ethernet or maybe IP... 

But that's a whole new set of problems and challenges<G>!


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## jaeroe (Jan 30, 2014)

i tested a protools HDX rig (pcie) against their thunderbolt hd native rig. got the same performance for my template (3 computers) with VEP and PT 10 and 11. (meaning the settings that did and didn't choke the host computer/DAW)

the weirdest part - i also have an apollo w thunderbolt card and that handles my template better with PT 11 and VEP in Protools.....

on the apollo, when i got the thunderbolt card i also upgraded to PT 11, but i was able to go from 512 buffer to 256. hard to say exactly where the benefit came from, although the TB card does seem to have a fair bit to do with it, as PT10 runs better on it too.


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## Nick Batzdorf (Jan 30, 2014)

> Playing VIs through MIDI is different, of course - several times longer.
> 
> 
> And that is the latency I am concerned with



But that's not audio latency, Jay, it's MIDI.

Changing the protocol you use for your audio interface will have a paramecium poop effect on your actual latency between playing a key and hearing the sound.

You know, if you have too much money then I have some far more useful suggestions about what to do with it than worrying about this crap.


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## Nick Batzdorf (Jan 30, 2014)

However, if what Larry says is true:



> I will say TBolt kicks ass in terms of being able to play a lot of voices at a low Kontakt buffer.



Then that's different. I have my doubts it's because of Thunderbolt, to be honest.


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## EastWest Lurker (Jan 31, 2014)

Nick Batzdorf @ Thu Jan 30 said:


> > Playing VIs through MIDI is different, of course - several times longer.
> >
> >
> > And that is the latency I am concerned with
> ...



It may make a least some difference in the buffer size you can use though perhaps, and that has a big effect on MIDI latency.


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## kitekrazy (Jan 31, 2014)

EastWest Lurker @ Tue Jan 28 said:


> Wow, you guys had really strong feelings about this.



So far it seems that way with hardware manufacturers on the PC side. I'm not fond of USB interfaces since just about everything else requires a USB port.


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## EastWest Lurker (Feb 4, 2014)

So, as usual, this turned into a column:
http://www.filmmusicmag.com/?p=12538


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## jaeroe (Feb 4, 2014)

Jay - very useful topic. great to get the conversation going.

just a heads up - your description of the Apollo Twin I/O isn't quite right. It has 2 mic pres, but has a total of 4 analog in plus light-pipe (which will do 8 channels of adat). it also has two discrete stereo output paths. you can (and in fact, the Protools Expert guys have tested) hook up additional i/o via light pipe. but, Apollo or Apollo 16 probably do make more sense if you need a lot of I/O.

ultimately it does come down to drive, and this will improve as time goes on. in Avid's case, i personally tested an HDX PCIe system (TDM) against their HD Native thunderbolt and they had the same performance (VI are afterall native). The Apollo Thunderbolt actually handles my template better/more efficiently, but that is because it runs under Core Audio versus AAE. just weird that Core Audio handles it more efficiently than Avid's engine, but it does. seems like it has to do with VEP, PT 11 and the dread protools CPU spike and error correct in Protools.

But, i'm now able to run at a 256 buffer in Protools and have VEP set to 1 buffer. this is a large template running over three computers. the most demanding seems to be U-He Dive, but I can run several instances of that. it works a lot more efficiently when you host Diva directly in Protools 11 versus VEP for some reason, though. that has stopped the dread CPU spikes.

before i bought the thunderbolt card for the Apollo i contacted UAD to ask them where the improvements could be felt, and the situation you described where you had to raise your buffer using their DSP is the biggest area of gain they said. the round trip for their DSP already has gains with thunderbolt and will have further gains with the new firmware update.


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## EastWest Lurker (Feb 4, 2014)

jaeroe @ Tue Feb 04 said:


> Jay - very useful topic. great to get the conversation going.
> 
> just a heads up - your description of the Apollo Twin I/O isn't quite right. It has 2 mic pres, but has a total of 4 analog in plus light-pipe (which will do 8 channels of adat). it also has two discrete stereo output paths. you can (and in fact, the Protools Expert guys have tested) hook up additional i/o via light pipe. but, Apollo or Apollo 16 probably do make more sense if you need a lot of I/O.



Thanks for the correction. I will update it.


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## NYC Composer (Feb 4, 2014)

The damn MOTU doesn't have Thunderbolt passthrough-one Tbolt port only. Major bummer.


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