Bandwidth requirements for Audio Interface

[ShiftStudios]

I was doing a bit of research today and found some information that was truly enlightening to me. I've always been relatively adamant about buying only Firewire audio interfaces so I could make sure I had enough bandwidth to meet my recording requirements, but then I actually did the calculations today because recently I bought an MOTU 828x and connected it to my windows laptop via USB2, did a stream test of 20 mics recording at once and didn't encounter a single hiccup. So it got me to thinking, how many tracks could I actually do? So I did the math.

Formula:
Bits per sample x samples per second = bits per second / 8 = Bytes per second.

I generally record at 48k 24bit (this isn't about "which recording setting is best, though I will cover it for you 96k guys too). So based upon that formula, for 20 tracks I would need to be able to get a minimum of 144KB/s per mono track, for a grand total of 2.8125MB/s or 22.5Mb/s. Considering USB2 has a theoretical maximum of 480 Mb/s but a realistic one of about 210Mb/s, even with 20 tracks, plus another 100% overhead, I'm not even close to hitting that.

So what about you 96k guys?

You would required 288KB/s per mono track which is a grand total of 0.28MB/s or 2.25Mb/s. So based upon that, if you were to max out the realistic actual bandwidth available on USB2, you'd need to hit 93 tracks at once, not leaving room for overhead, you want to leave 100% for overhead, you can still run 45 tracks.

I don't know about you other home studio guys, but I feel like the whole Firewire/USB arguments is mostly invalid for us. Considering I'd never do more than maybe 24 tracks at once, I don't feel I'd ever hit even the realistic maximum throughput of USB2, let alone Firewire...

So honestly, though the numbers are technology may have been in favour of Firewire back in the USB1 days with slow processors, I think in our current day and age (of USB3.1), even USB2 interfaces are more than sufficient for 90% of home studio guys and the "Firewire benefit" is really not a thing anymore.

Anyone else done the math on this and found the same?

[mesaone]

You haven't factored in the output streams. It might not matter due to the way USB buffers, but the latency certainly is different.

I have an audio interface that can connect through either USB or firewire. Lower latency is achievable when using firewire.

[Park Seward]

Compare USB CPU usage vs. Firewire. You'll see USB puts more demand on CPU processing.

"Although high-speed USB 2.0 (theoretical speed 400 Mbit/s) nominally runs at a higher signaling rate than FireWire 400 (theoretical speed also 400 Mbit/s), data transfers over S400 FireWire interfaces generally outperform similar transfers over USB 2.0 interfaces. Typical USB PC-hosts rarely exceed sustained transfers of 280 Mbit/s, with 240 Mbit/s being more typical. This is due to USB's reliance on the host-processor to manage low-level USB protocol, whereas FireWire delegates the same tasks to the interface hardware (requiring less or no CPU usage). For example, the FireWire host interface supports memory-mapped devices, which allows high-level protocols to run without loading the host CPU with interrupts and buffer-copy operations.
Besides throughput, other differences are that it uses simpler bus networking, provides more power over the chain, more reliable data transfer, and uses fewer CPU resources.
FireWire 800 is substantially faster than Hi-Speed USB, both in theory and in practice."

http://www.diffen.com/difference/FireWire_vs_USB

[ShiftStudios]

Okay, lets factor in output streams. Even with 20 in and 20 out, we're still only talking 45Mb/s, still far shy of the realistic bandwidth at 48k or 90Mb/s at 96k. I'm not debating that Firewire is faster, or more efficient, because with a good chipset there is no question about that. I'm just stating for the majority of home studio guys, USB2 or Firewire generally shouldn't matter enough to be a dealbreaker.

Also, most hardware these days have onboard DSP that allow you to do realtime monitoring. I can honestly say in all my years, between Audio Interfaces and outboard gear, I have rarely had a need to be concerned with latency in my sessions. I don't generally run audio through plugins when recording, and I'm a strong advocate of getting it right at the source.

Considering I have both a Focusrite Liquid Saffire 56(firewire) and an MOTU 828x(usb2) I can say with confidence that they both function more than adequately for studio use. :)

In regards to latency, I have not noticed a significant enough difference for it to matter (eg. 9ms vs 11ms). And in regards to CPU, that mattered on USB1 and older CPUs. Considering most PC's these days have multiple cores and threading, for example my laptop has an i7 with four cores /w threading for a total of 8 virtual cores. I'm not overly worried about the extra 2% in processing power when you consider how much more power and speed the current generation of CPUs have.

For people who run a lot of VI's, this may be different story if you don't have a powerful enough computer, but then you'll most likely have other problems too. Or maybe people who run crazily high format (eg. 24bit 192k), they'd probably benefit from it as well.

Again, I'm not stating that firewire is not faster or more efficient with the right chipsets, I'm just saying for the majority of users, a USB2 interface on a current generation machine should be adequate for most people as it is capable of more than enough bandwidth to cater to 16 x 16 or 24 x 24. :)

[mesaone]

Originally Posted by ShiftStudios

In regards to latency, I have not noticed a significant enough difference for it to matter (eg. 9ms vs 11ms)

That's an 18% reduction in overall latency. I would call that significant.

Originally Posted by ShiftStudios

I'm just saying for the majority of users, a USB2 interface on a current generation machine should be adequate for most people

I agree with you there.

[ShiftStudios]

Originally Posted by mesaone

That's an 18% reduction in overall latency. I would call that significant.

Percentage seems significant, yes. But latency matters to ears, for a player. And I can't feel a difference between 9ms and 11ms when playing, so it's still sufficient to me. Since that was only at 128, I'm not sure what lower or higher would yield.

Originally Posted by mesaone

I agree with you there.

I guess at the end of the day it's about the users preferences as always. I just wanted to highlight that standards in the way data is handled aside, USB2 has more than enough bandwidth available to cater to almost any home studio setup. :)

Just thought the math was interesting and wanted to share.

[Darryl Ramm]

One thing that is interesting in thinking about these things is modern Thunderbolt interfaces are down to a few ms latency. If they can maintain that under a decent host load that is stunningly impressive performance.

I would love to see some real-world measurement of latency on the Apogee Ensemble Thunderbolt with Pro Tools. Unfortunately the Pro Tools Expert review (and I think those guys do a good job of lots of stuff) of that interface seemed pretty confused about measuring actual latency vs. ADC.

[Amack]

Then I guess you would also be impressed with the performance of Roland's Studio Capture ($999) - right? See the attachment to post #30 at http://duc.avid.com/showthread.php?t=363163&page=3.

Originally Posted by Darryl Ramm

One thing that is interesting in thinking about these things is modern Thunderbolt interfaces are down to a few ms latency. If they can maintain that under a decent host load that is stunningly impressive performance.

I would love to see some real-world measurement of latency on the Apogee Ensemble Thunderbolt with Pro Tools. Unfortunately the Pro Tools Expert review (and I think those guys do a good job of lots of stuff) of that interface seemed pretty confused about measuring actual latency vs. ADC.

[albee1952]

Don't forget, with USB2, the claimed rate is "burst" speed, not sustained(FW speed is sustained). Not sure where USB3 sits on this little detail

[JCBigler]

Just wait until Ethernet based audio interfaces become as ubiquitous as USB and FireWire are.

Dante will push 512 channels in both directions at 24bit/48kHz (on a gigabit network).