Audio Over IP products are becoming more common in the recording studio, with several competing formats available, namely AVB, Dante and RAVENNA. I have been provided with a brace of three products that support the AVB (Audio Video Bridge) Audio over IP standard, namely the petite but powerful RME Digiface AVB audio interface as well as the RME AVB Tool audio converter and RME 12Mic mic preamp for this product review. I’ve been interested in audio over ethernet technology for some time and have a fair amount of experience running my own Dante network but this is my first time using AVB products.
AVB In Brief
AVB is essentially an extension to the IEEE 802.1 ethernet standard and it is deterministic in nature, which means that packets are guaranteed to be delivered to their destinations on time.
Looking at Audio over Ethernet more broadly, for most people using AoIP technology in the recording studio the advantages of either technology will afford high channel counts, 100m cable runs using relatively cheap ethernet cable, easy scalability and advanced routing capabilities.
By way of comparison, Dante works a little bit differently in that packet delivery is done on a “best effort” basis- there is no guarantee to the timely delivery of packets intrinsic in the technology. Dante instead uses a function called Quality of Service (QoS) to prioritise some packets over others. With AVB the precisely timed delivery of packets is part of the standard.
You may be aware from my previous articles that I run a 64 channel Dante network which is moderately large in studio terms, but compared the to maximum number of channels possible it is relatively tiny. As such I’ve never had any issue running the maximum number of channels I have available to me on my converged network (that is running, data, video and audio on one network).
The advantage with a deterministic networking model becomes more apparent when running very high channel counts that are approaching the total limit of the network. An AVB capable network reserves some bandwidth in order to guarantee that packets are delivered on time. However, even when running smaller channel counts there is certainly an advantage to a deterministic network, purely for peace of mind that a sudden spike in network traffic will not derail a recording session that is in progress. It is also worth bearing in mind that, unlike Dante, AVB is an open standard.
There are a couple of requirements for AVB to work, the main one being that AVB compatible switch must be used. This requirement can sometimes be a stumbling block for some installations, in that you generally cannot simply upgrade an existing switch to support AVB, you have to replace the switch with one that supports AVB. Fortunately many options exist from portable 5 port switches through to rack mount, high port count switches from major industry players such as Cisco, Extreme Networks, Luminex, Netgear, amongst others.
For the purpose of this article I physically separated my Dante network from the AVB network in order to get up and running quickly. It is possible to run the two technologies on the same network, provided the switch technology is AVB compatible. Due to the nature of an AVB switch the AVB packets will be prioritised over Dante, but it is also possible to create a separate VLANs for the AVB and Dante traffic.
RME Digiface AVB Hardware
The £799 RME Digiface AVB audio interface is a compact device measuring just 11.2 x 8.3 x 2.6 cm with just USB, ethernet, headphone and word clock connections so you could be forgiven for thinking that it was a simple portable audio interface. It is much more than that.
The bus powered USB 3 Digiface AVB is capable of an astonishing 256 channels of audio, 128 channels input and 128 channels of output, at 44.1/48 kHz sample rates. As you would expect this channel count is halved to 64 channels each way when recording at 88.2/96 kHz and halved again to 32 channels each way at 176.4/192 kHz. The Digiface AVB will also support USB 2 with a reduced channel count of 64 channels.
If used alone the only audio output the device has is a 1/4 headphone jack although it is worth noting that this can be repurposed as a line level output with a 1/4 to RCA splitter cable, although the signal will necessarily be unbalanced.
The Digiface also supports RME Total Mix FX digital mixer, although it is not one of those devices that supports DSP processing (EQ, compression, reverb etc) as you would find on the Babyface Pro, Madiface XT amongst others. This is an understandable compromise and certainly onboard DSP would increase the size and price of the unit.
The Digiface AVB is then a compact, portable audio interface supporting AVB that must be expanded by other AVB devices in order to be a complete recording package.
Installing The Digiface AVB
As my Operating System of choice is Mac OSX I first installed the Digiface AVB on the latest version of Catalina (OSX 10.15.5) running on a 2019 Mac Pro. Installation is comprised of the following components:
1. Install the Digiface AVB Driver (including Total Mix).
2. Install the RME AVB Controller Software
There is an additional RME USB Series Flash Tool that can be used to upgrade the devices firmware, but as the device was on the latest firmware this was unnecessary.
After rebooting the machine the Digiface AVB shows up in Audio Midi Setup as a 128 channel capable audio interface.
The software installs the ‘Fireface USB Setting’ application where you have minimal adjustment over device, namely setting word clock and USB3 Bus settings as pictured.
Beyond that the rest of the Digiface AVB’s configuration is done in two places- Total Mix and the RME AVB Controller.
Total Mix is essentially a software mixer that allows you to route and monitor incoming audio before it runs through your DAW’s audio buffer, allowing for near zero latency cue mixes. I won’t go into details about Total Mix as part of this review, it has been discussed at length over the years but let me say it does its job extremely well.
RME AVB Controller is an application that allows you to route signals between different devices. In AVB-speak it is known as IEEE 1722.1 AVDECC, or an AVDECC Controller.
These connection in RME AVB Controller are done by assigning an Output Stream of one device to the input stream of another. Say you had 8 channels of Output from the Digiface AVB available and wanted to connect them to an 8 channel Input Stream on the AVB Tool, you would navigate to the AVB Tool on the left side pane of the RME AVB Controller and assign the Output Stream from the Digiface to the AVB Tool’s Input Stream. Note that this is not necessarily routing audio to a physical input or output on the device, it only connects Output Streams to Input Streams, in a way it works like an analogue patchbay. You still need to connect physical inputs and outputs to the other end of the Input and Output Streams for audio to be passed.
This assignment of physical ports on devices to Input and Output Streams is now in another place, which is the RME Remote, accessed by using a web browser to navigate to the IP address or device name (such as http://avb-tool.local.) of a device with inputs or outputs. If you have multiple AVB devices you will need one tab per device. It is also where you can make changes to the device’s XLR/TRS state, preamp level, polarity and phantom power state and other functions. These can also be controlled from the device front panel, of course. One slight annoyance is different tabs will be shown in the web browser will the same name, which is "RME Remote”.
As part of the review I had two IO devices and in switching between the different tabs it was easy to remember which one was which in the browser.
In larger AVB Installations it might becomes a bit unmanageable.
It would be a helpful update to the RME Remote application to have it pull the device name to the tab title and make navigating between devices much more streamlined. I have been assured by RME that this is on the TO DO list and will be forthcoming in a later release.
This brings me to an observation about the RME ecosystem, which is that it sometimes feels a tad fiddly, Between RME Remote, RME Controller, Fireface USB Settings and Total Mix (as well as the DAW itself) I found myself flicking between many different places to do things. For example, say you want to attach a new piece of equipment, set some preamp levels and and route audio to headphone sends, the process would be this:
1. Connect physical inputs/outputs to IO Streams in RME Remote (web based).
2. Connect IO Streams between devices in AVB Controller.
3. Set up cue mix in Total Mix.
4. Go back to RME Remote to set levels, engage phantom power etc for preamps.
I’d like to see this streamlined down to one or two places in order to control the devices. That said, once it is all set up and working you do tend to flick between the DAW, RME Total Mix and the RME Remote tabs for most functionality.
Digiface AVB Native Latency
Latency figures for the Digiface AVB are very good indeed.
At 44.1 khz, using a buffer size of 64 samples Logic Pro X reports the Digiface RME Output latency as 2.2 ms and roundtrip latency as 4.4ms, putting it firmly in the top end of audio interfaces in terms of low latency performance.
If your needs require lower latency then you can use RME’s Total Mix FX mixer in order to monitor audio from hardware. Total Mix FX is a comprehensive digital real-time mixer allowing fully independent routing of input and playback channels to all physical outputs. This allows the user to create completely independent headphone/monitor mixes, with snapshot and groups functionality built in. It is very powerful compared to the most competitor products.
I would like to see individual device control, such as Mic Preamp control brought into Total Mix FX at some point in the future.
RME AVB Tool
The RME AVB Tool (£1479) is compact, half rack space audio converter that speaks several different formats- analogue audio, coaxial MADI (optical is an option) and AVB. It is classed as an ‘audio converter’ by RME and not an audio interface, as although it has a USB port on the rear, it is not for communication to a computer for the purpose of passing audio, but rather for for firmware updates and remote control.
The AVB Tool features 4 analogue inputs on XLR/TRS combo connectors (+18 dBu, 75 dB gain) with switchable Mic/Line/Hi Z, a headphone output on its front panel, along with a colour TFT display. Around the back you get an ethernet port, 2x TRS balanced Line Out (+4/+19 dBu, DC coupled), word clock IO (BNC), 2x coaxial MADI ports and a space for an optical MADI SFP to be added. It is powered by an external 12v 2.0A power supply with a locking connector (a nice touch- I wish more manufacturers would do this).
There is also a USB port on the rear of the unit but unlike the Digiface AVB this connector does not pass audio to the computer- it is for remote control and software updates only. Mac owners can, of course, connect directly to the AVB Tool (or indeed any other AVB product) directly via ethernet as AVB is built into Mac OSX, but PC users will need some sort of PC to network connection (such as the Digiface AVB) in order to pass audio to the unit.
The AVB Tool also features RME’s ‘super low jitter reference clock’ SteadyClock FS first seen in the ADI-2 DAC.
AVB Capability is up to 8 streams (of up to 8 channels per stream) for input and output, giving a total of 128 channels in total. The AVB Tool’s internal signal router has 260x260 channel capability. The numbers here are simply mind boggling.
Connecting the AVB into my existing setup was as simple as connecting power, running an ethernet connection to the AVB approved ethernet switch and the master outputs to my monitor controller. After assigning the analogue inputs and outputs to AVB streams in RME Remote and then used RME AVB Controller to connect the AVB Tools AVB Streams to the Digiface AVB and set the master clock.
The DAW doesn’t see the AVB Tool as a device, the computer connection is done via the Digiface AVB, so it is a good idea to label your inputs/outputs in the Pro Tools IO page (or whichever DAW you are using).
Who Is This RME AVB Tool For?
The AVB Tool is a little unusual in that it doesn’t have a direct computer connection for the purpose of passing audio so it cannot really function as an all in one audio interface.
If you wanted to use it directly with Mac OSX you can use the onboard AVB stack but your Mac would need onboard ethernet to do this or you would use a USB to Ethernet dongle.
As a portable solution the combination of AVB Tool with Digiface AVB + AVB Switch is a pretty capable system, with the ability to expand the inputs and outputs with other devices as you see fit. In many ways it is an expression of the modularity of AoIP devices.
The lack of direct computer connection is a slight pity- if the AVB Tool had this functionality then it would be a great ‘one box’ solution for location recording. As it stands you would need at least two other boxes (an AVB approved switch and an AVB audio interface such as the Digiface AVB) in order to achieve this on a PC and I’d usually recommend the same on a Mac.
Given its ability to bridge between MADI and AVB it is a very neat way to get MADI devices (potentially up to 256 channels of MADI) onto an AVB network and vice versa.
I could also see the AVB Tool being used in the edit suites of larger (MADI or AVB capable) facilities when all you need is a few mic preamps and a pair of outputs direct to some monitors.
I’ve been informed by Synthax, RME’s UK Distributor, that RME consider this to be a step up from previous devices in terms of sonics and clocking and I believe them- it sounds excellent . The mic preamps are crisp and clean with 75dB of gain available - more than enough for all but the most gain hungry ribbon microphones. Audio output is similarly transparent- it is a great sounding unit.
Analogue Input Specifications
XLR in 1-4
Input Impedance: 3.4kOhm
Gain Range: 75 dB, 1dB steps
Resolution AD: 24bit
Frequency Response @ 44.1khz, -0.1 dB: 8 Hz - 20.8 kHz Frequency Response @ 96khz, -0.5 dB: 4 Hz - 29.2 kHz Frequency Response @ 192khz, -1 dB: 3 Hz - 43.7 kHz
THD @ 30dB gain: < -110 dB, < 0.00032%
THD+N @ 30dB gain: < -104 dB, < 0.00063%
Channel separation: > 110 dB
Signal to Noise ratio (SNR): 119 dB RMS unweighted, 121 dBA Maximum input level, Gain 0 dB: +18 dBu
Maximum input level, Gain 75 dB: -57 dBu
TRS in 1-4
As above, but:
TRS jack, balanced
Gain range: 42 dB, 1dB steps
Maximum input level, Gain 8dB: +21 dBu
Maximum input level, Gain 50dB: -21 dBu
Switchable high impedance (unbalances TS): 1MOhm
Analogue Output Specifications:
Phones 1/2
Resolution: 24bit
Noise (DR): 115 dB RME unweighted, 118 dBA
Frequency Response @ 44.1khz, -0.5 dB: 9 Hz - 22 kHz
Frequency Response @ 96khz, -0.5 dB: 9 Hz - 45 kHz
Frequency Response @ 192khz, -1 dB: 8 Hz - 75 kHz
THD+N: <-100 dB, < 0.001%
Channel separation: > 110 dB
Output: 6.3 mm TRS Stereo (unbalanced) or mono (balanced) jack
Maximum output level at 0dBFS: +13 dBU (unbalanced), +19 dBU (balanced)
Analogue Out 3/4
Output: two 6.3mm TRS mono (balanced) jacks Maximum output level at 0dBFS: +4 dBU pr +19 dBU
RME 12Mic
The final device I’ve been investigating is RME’s 12Mic, rack mount mic preamp, which retails for £2399. The 12Mic has a complement of 12 Mic preamps with up to 75dB of gain and accepting signals up to +18dBu, four on combo XLR/TRS inputs which are switchable to Hi Z and the remaining eight on female XLR’s. Other than the headphone output (which can be repurposed as a stereo output) the unit has no other analogue audio outputs. It does have the same AVB and MADI capabilities as the AVB Tool, as well as word clock and a three pairs of ADAT optical outputs.
The ADAT optical ports can each send the expected maximum of 8 channels, which drop down to 4 or 2 at double or quad sample rates respectively. ADAT output is an interesting option, allowing interfacing with many audio interfaces with ADAT IO including RME's own Digiface USB. Given that the devices allow sources to be routed to multiple destinations at once it allows for a degree of redundancy- you could have the mic preamps go out to an AVB stream, to a MADI destination and an ADAT output all concurrently. The integrated routing matrix is hugely flexible.
In addition it features an internal power supply, which a backup possible via an external wall wart (not supplied). In keeping with the ‘pro’ spec of the units AVB ethernet connections feature primary and secondary ports, for redundant operation. Unlike some Dante devices the secondary port cannot be used as a switch for connection to other devices.
The 12Mic also features a USB connection for remote control and updates, as with the AVB Tool it does not stream audio signals.
The 12Mic is a fantastic analogue front end for tracking bands- cost per preamps puts it around £200 before you take into account all the other functionality it contains. By comparison to other AoIP mic preamps, such as the Focusrite MP8R, is more expensive than the 12Mic, has only 8 preamps instead of the 12Mic’s 12 and has none of the routing matrix, ADAT, MADI, headphone capabilities of the 12 Mic. By comparison the 12Mic looks like an absolute bargain.
The 12Mic would be easily at home in the tracking room or in the control room. Placement in the tracking room would make a lot of sense, allowing for short cable runs from the 12Mic to the microphones, with a single ethernet cable running back to control room where it can be managed via RME Remote.
Analogue Input Specifications:
XLR in 1-12
Input Impedance: 3.4kOhm
Gain Range: 75 dB, 1dB steps
Resolution AD: 24bit
Frequency Response @ 44.1khz, -0.1 dB: 8 Hz - 20.8 kHz Frequency Response @ 96khz, -0.5 dB: 4 Hz - 29.2 kHz Frequency Response @ 192khz, -1 dB: 3 Hz - 43.7 kHz
THD @ 30dB gain: < -110 dB, < 0.00032%
THD+N @ 30dB gain: < -104 dB, < 0.00063%
Channel separation: > 110 dB
Signal to Noise ratio (SNR): 119 dB RMS unweighted, 121 dBA Maximum input level, Gain 0 dB: +18 dBu
Maximum input level, Gain 75 dB: -57 dBu
TRS in 1-4
As above, but:
TRS jack, balanced
Gain range: 42 dB, 1dB steps
Maximum input level, Gain 8dB: +21 dBu
Maximum input level, Gain 50dB: -21 dBu
Switchable high impedance (unbalances TS): 1MOhm
Analogue Output Specifications:
Phones 1/2
Resolution: 24bit
Noise (DR): 115 dB RME unweighted, 118 dBA Frequency Response @ 44.1khz, -0.5 dB: 9 Hz - 22 kHz Frequency Response @ 96khz, -0.5 dB: 9 Hz - 45 kHz
Frequency Response @ 192khz, -1 dB: 8 Hz - 75 kHz
THD+N: <-100 dB, < 0.001%
Channel separation: > 110 dB
Output: 6.3 mm TRS Stereo (unbalanced) or mono (balanced) jack
Maximum output level at 0dBFS: +13 dBU (unbalanced), +19 dBU (balanced)
Direct Mac Connection
As previously mentioned on PC you will need an AVB capable audio interface such as the Digiface AVB in order to route audio to and from the computer. Mac users have a degree of flexibility beyond this as AVB is written into Mac OSX. There are a couple of ways to do this.
The first is to connect the Mac directly to a device via ethernet and then navigate to the Network Device Browser in Audio MIDI Setup and acquire the desired device, which will then show up in Audio Devices. The only problem with doing so is this only allows one AVB device to be acquired by the Mac’s AVB stack, as the Mac will lock to that particular AVB device to the exclusion of all the others.
There is a better, if slightly complicated way to do it which is to setup your computer as an AVB endpoint.
You do this by opening Apple’s somewhat hidden AVB Audio Configuration utility by going to the Terminal (found in Applications/Utilities folder) and typing in “avbutil —controller”. Note the two dashes together before controller.
This opens up the AVB Audio Configuration utility. I suggest you rich click this icon in the dock and get it to ‘Keep in Dock’.
You then can select ‘Simple Virtual Audio Configuration from the Window drop down menu.
This will then allow you to enable an ethernet port on your Mac as an AVB End Point. On my 2019 Mac Pro I have two ethernet adapters, one for my Dante network and another for the AVB network
Once you have done this you will see the Mac Pro device both in the RME AVB Controller and in Audio Midi setup. It is then simply a matter of connecting the output streams in the AVB Tool (or any other AVB device) to the Mac Pro’s Input Streams and vice versa. The AVB Tool can now be used as an IO source without the need to use the Digiface AVB. Using the Mac Ethernet port as an AVB End Point will give me a maximum of 64 channels of input and 64 channels of output, configured as 8 streams of 8 channels.
In a way it works not unlike the Dante Virtual Soundcard, which is an application that turns your computer’s ethernet port into an audio IO source, but because AVB is written into Mac OSX it is capable of lower latency than Dante Virtual Soundcard.
At 44.1kHz the direct connection method achieved an output latency of 2.0ms and a roundtrip of 5.8ms. This is pretty impressive- the output latency is actually slightly better than via the RME Digiface AVB and roundtrip is certainly close enough for rock ’n roll.
Also, because the computer is an AVB end-point I am still able to connect other devices. As you can see below I have routed the AVB Tool and 12Mic in as Input Streams 1 and 2.
The one downside to using the Mac as an AVB end point is that, as you are bypassing the RME Digiface AVB, you no longer have RME’s Total Mix FX software mixer available to you for near zero latency monitoring. The same is true when using the “acquire” mode of connection to a single device.
PC Connection:
Given RME’s reputation for PC drivers with excellent stability I had to look at how well the Digiface AVB ran with a Windows operating system. For the purposes of running the test I used a Dell XPS13 laptop with i7-855U, 16GB Ram and a 500GB SSD. Driver version on Windows 10 Home V 1909, OS Build 18363.900.
Installation of the driver was a painless affair and after a reboot the Digiface AVB Shows up as an ASIO device in your DAW of choice, in this instance I used Samplitude Pro X4. WDM drivers are available and have to be enabled in the control panel- on Windows it is called “Madiface Series Settings” which is positioned in the Windows Taskbar notification area.
Latency at 44.1 kHZ with a buffer of 64 samples was reported by Samplitude X4 as 3ms on output and 5ms roundtrip.
I can happily report that the PC drivers are very stable- no crashes were encountered nor were there any clicks or pops experienced. Given some Audio over Ethernet products are Mac only (I am looking at you, Focusrite Red series) it is pleasing to see a company truly support their products on both Mac and PC platforms. Bravo RME.
Problems Encountered
I did have a couple of issues getting the system up and running which I will admit were largely of my own making but I’ll detail them here as a way of highlighting a few potential pitfalls with multi-device interconnection. The first was that running multiple computers as part of the test procedure I had set the Digiface AVB as an ‘acquired’ device in Audio Midi setup. A silly mistake that gave me a day or so worth of head scratching which RME were graciously able to help me resolve. This does highlight an issue with multi-room studios that are all interconnected via the network, which is that it is possible for computers to take ownership of a device via the acquire mode in a way that might not be immediately obvious. There are good networking practices that can overcome this - such as setting up a VLAN, or to only allow known devices on the network by way of Mac Address filtering, and those facilities with a dedicated network engineer will probably be fine.
One other issue I’d like to mention is a potential memory leak in the RME Remote software. When first loaded in Safari 13.1.1 the RME Remotes used around 120MB of RAM. The longer these Remotes were active they larger their system RAM use became, getting sometimes as high as 800MB per tab. On a beefy system it probably wouldn’t be noticed but those using more modest computers may find it to be problematic. I fed this back to RME and was provided a beta- firmware for the AVB Tool and 12Mic but unfortunately the problem remained for the duration of the test. The work around for this is to refresh the web browser.
Pricing
The RME Digiface AVB retails for £799, the AVB Tool for £1479 and the 12Mic for £2399. None of these products are what you could call ‘cheap’ but considering what you get for your money I’d say they represent excellent value. Very few products offer the amount of IO plus multi format conversion that RME offer at the profile point they offer it at. The way RME design these products you will probably be looking at purchasing more than one of them in order to get a complete recording solution, plus you do need to factor in an AVB switch.
Summary
I’ve enjoyed using these three RME AVB products immensely. I’d like to highlight something I mentioned at the start of this article which is each of these products fulfils a different role in the AVB ecosystem- the Digiface is primarily an audio interface, the AVB Tool is primarily a digital converter and the 12mic is designed to be a professional rack mount multichannel mic preamp. As such they do their respective jobs extremely well.
RME have taken a different approach to other manufacturers of audio over ethernet audio interfaces in their decision to make the Digiface AVB a small simple device with no analogue audio inputs and minimal audio outputs. The Digiface AVB’s size versus its channel capability is quite remarkable- this little box is capable of an awful lot for the relatively cheap purchase price of £799. Granted you will need some sort of analogue front end to go with it, such as the £1479 AVB Tool. As a package of two products you get an awful lot of power for around £2278.
The 12Mic is a high quality front end for any AVB or MADI based studio- having enough preamps to track an entire drum kit and perhaps even an entire band.
RME have a reputation for high quality products with extremely stable drivers and are known to support their products for a long time. I’m pleased to see these products continue that tradition and I’d personally be comfortable investing in the brand were I be looking to build a studio around AVB. We do not yet know what will happen with the competing Audio over Ethernet formats- will AVB or Dante end up being the dominant format, or will the two formats co-exist in the industry each taking a piece of marketshare? I’m not about to make that prediction here - I guess we will see what develops. Certainly these products from RME are strong products, with excellent drivers and a clean neutral sound. If you are looking at an AVB based installation, or already running a MADI-based studio then I’d urge you to book some time with your local retailer to investigate them more fully.
Digiface AVB
Pros
Small in size but big on channel count.
Bus powered.
Cons
Would have liked a couple of channels of audio input.
RME Tool
Pro
Fully featured front end for AVB networks
Ability to work as a single box solution for Mac owners. Can act as a bridge between MADI and AVB.
Excellent audio performance.
Con
No USB audio streaming.
RME 12Mic
Pros
High quality front end for AVB Networks. Can act as a bridge between MADI and AVB. Excellent audio performance.
Cons
No USB Audio Streaming.
A pair of dedicated analogue outputs would allow it to work as a single box solution.
RME AVB Ecosystem
Pro
Professional deterministic networking solutions for the quality conscious.
Added multi-format (MADI and ADAT) bridging thrown in for good measure.
Con
Switching between RME Remote, Total Mix and and the AVB Controller can feel fiddly at times. Not the cheapest solution out there but the quality of the products justifies the financial outlay.