can i use 2 firewire audio devices @ same time?

You can combine several devices by creating an Aggregate device in the Audio Midi setup of your Mac. here is a link to a page describing this procedure very explicitly:

http://support.apple.com/kb/HT1215

You definitely can have two FW devices on the same FW bus.

Has been a feature since Tiger was introduced. Works fine with good drivers.

Cheers

Hi Steven,

I've used 4 separate firewire interfaces on the same firewire bus however if you start using higher sample rates the number you can have connected on the same bus at the same time drops.

I found I could use only 2 reliably at 96k and 1 to 2 at 192k. The firewire transport is a bandwidth hog - even if you are not passing audio an 8 channel analogue device with say another 2 channels of AES digital and 8 ADAT can require a total 36 audio streams (in+out). By the time you start factoring higher sample rates the required data stream soon approaches and surpasses the 50MB/s (400mb/s) and 100MB/s (800mb/s) limits.

The best solution is not to use firewire hard drives if you have a firewire interface or to have a second firewire bus through the installation of a PCI firewire card. (The Apple FW 400 and 800 connections are all on the same bus) If you want multiple firewire interfaces and high sample rates then you'll probable want 2 firewire busses for just the interfaces with audio recorded on e-sata or an internal drive.

Regards

Julian

Julian Scott wrote:

The best solution is not to use firewire hard drives if you have a firewire interface or to have a second firewire bus through the installation of a PCI firewire card. (The Apple FW 400 and 800 connections are all on the same bus) If you want multiple firewire interfaces and high sample rates then you'll probable want 2 firewire busses for just the interfaces with audio recorded on e-sata or an internal drive.

Regards

Julian

Sorry Julian, this doesn't make sense to me; could you clarify please for 'a bear with little brain'.

Thanks

Hi gilapuki,

When you are using an audio interface the driver "publishes" the number of channels available at the interface to the host software. In the example of a lot of 8 channel interfaces this might be 8 inputs of analogue, 8 inputs of multitrack digital (ADAT) and 2 channels of Spdif or AES and the same again for outputs. For these respective inputs and outputs to be available to the computer data bandwidth (audio transport) has to be utilised between the computer and the audio interface.

In the example above, for example with typical MOTU or Metric Halo interfaces, with 18 inputs and 18 outputs appearing in Logic (they will appear automatically just by selecting the interface) Each input requires 4608 kb/s of data, each output requires 4608 kb/s so just connecting a single interface requires 36 data streams (18 in, 18 out) of 4608 kb/s, Therefore connecting a firewire single interface set to 96k/24 bit will use up 36x4608 kb/s - 165.888 Mb/s. This happens to be over 40% of the theoretical bandwidth of FW400. This is before any audio is written or read from disc by the host programme.

This is why it is a good idea if possible to have the disc writing streams on a separate bus from the audio transport.

So again using the example above if you were playing back a session with 40 mono tracks of 96k/24 bit audio which is well within the abilities of a single modern hard disc the data bandwidth required will be 166.888 Mb/s of firewire transport and 184.320 Mb/s of audio file data. So a simple 40 track recording will be almost maxing out a FW400 bus (any firewire bus is restricted to the data rate of the lowest connected component - so a Metric Halo FW 400 interface will restrict the complete firewire bus to 400 even if there are FW800 drives connected). Also FW400 and FW800 are theoretical limits rarely achieved in practice. The most likely result of this situation will be clicks and pops and occasional drop outs of audio or CPU/disc overloads.

The above figures are the reason it is often better to not record audio to disc on the same bus as the firewire interface but to spread the load across other busses.

I hope this rather wordy response makes sense to you!

Regards

Julian

Thank you. All that makes sense. As my recording sessions rarely involve more than three tracks of audio, I haven't come up against the limitations you describe so well.

Hi Julian,

I've got a "big" multitrack venue coming up. I wil use one fire wire 400 with 3 Metric Halo 2882 interfaces connected, and 2 more M-Audio 2626 through Adat toslink connected to the MIO's.
24 bit/48Khz to record 40 channels of audio. Should I go for an express card with fire wire 800 or
e-Sata to get my HD on another bus? I will use this system as a backup, on my MacBook Pro, for the two multitrack machines we are gonna use as main.

Kind Regards,

John

Hi John,

I think both would be fine. I currently use e-Sata a lot and it has proven to be rock solid. It might be a good idea to "soak test" your recording set-up prior to the recording with the interfaces and drives set up exactly as they will be for the event. Just record say 50 - 55 channels of audio (can be tone or even silence) and check it all works smoothly.

If you're recording is extremely important and missed cues wold be a disaster Id think about running a back up system even if it's just stereo.

Regards

Julian

Hi Julian,

Thank you for you reply. I did a recording with 40 channels (silence) while my Lacie was connecten on the same bus, firewire 800. I did connect a stereo source to check after one hour for drops, but no problems at all. I will get me an e-Sata Express card just to be sure. This system is the a back up system for two Alesis HD 24's.

thnx again, and happy new year!

Regards

John