First published in Resolution, March 2021
In the 15 years since he founded FiLO Classical, recording engineer Dave Rowell has consistently garnered praise — and no small number of awards — for his artistic and technical skill in location recording and broadcasting classical music. Known both for delivering excellent recorded sound and for his calm, no-nonsense approach to recording, Rowell has worked with a remarkable array of artists and ensembles across Europe and beyond to refine and craft performances captured on session.
Rowell’s musical ear and his expertise in working with Merging Technologies’ Pyramix, his preferred editing software, are two drivers of his success, along with his commitment to using the right gear for every project. Always optimising his recording kit to address the complexities of various performances and venues, Rowell has moved toward a RAVENNA-based real-time audio-over-IP (AoIP) solution built on Merging Technologies’ Horus, Hapi, and Anubis boxes.
“My journey into RAVENNA started through Merging Technologies and their Pryamix editing software,” says Rowell. “When the company released the Hapi, its second RAVENNA-based interface after the Horus, I saw an opportunity to get into the RAVENNA system. Gradually, as the gigs got bigger and more complicated, it was no longer viable to rely on a mixed system of MADI and RAVENNA.”
Ultimately, Rowell built a system comprising two Horus, three Hapi, and two Anubis interfaces, with two Artel Quarra Precision Time Protocol (PTP)-aware ethernet switches, one rack-mount unit and one stand-alone unit that can be used as a hot-swappable spare. He was the first Hapi user in the UK, and he is among the few so far to run a complete RAVENNA system both in the studio and the control room.
Addressing AoIP’s PTP Requirements
For a live recording in a concert hall, Rowell might have a Hapi interface with mic cards in the roof, a Horus interface on stage, and then perhaps a third interface for offstage performers. With RAVENNA interfaces in each place, ethernet is converged to fiber and then run back to a switch feeding out to the control room, be it a large dressing room backstage or a production truck outside.
Rowell is undaunted by the prospect of a gig with 60+ channels. He typically works at 192kHz and, at this sample rate, the Quarra switch gives him 256 paths, more headroom than he’s ever likely to need. However, with several signals coming from different sources and the added complication of return signals for talkback and a light relay system for the studio, Rowell works with a lot of bi-directional connections over varying distances and cable lengths.
“It’s at this point that unaware-PTP switches can’t cope,” says Rowell. “They can manage with simple systems but struggle with more complex networks. Sadly, the giveaway that it is struggling is when the PTP clocking drops, causing the loss of all audio signals. It can be a fatal situation where the network is fully functional and stable in testing, but then, for no discernible reason, the PTP clock is lost and the network falls apart. The only option is to go with a PTP-aware switch as reliability is critical in all recording environments.”
One benefit of AoIP is that the network switch allows all devices on the network to talk to one another. With a proven protocol such as RAVENNA, hundreds of channels of real-time audio can be transported at incredibly low latencies. However, in audio recording applications involving a significant number of endpoints, a PTP-aware switch is essential for reliable handling of the PTP and to ensure the synchronisation of all audio streams.
“In the audio world, with digital front ends coming over fiber from lots of different locations, reliable clocking is essential,” says Rowell. “Moving from a MADI system to a RAVENNA network with a non-PTP-aware switch caused a noticeable increase in clocking drift — using MADI it was around 3 nanoseconds, which increased to 300+ nanoseconds using PTP. Additionally, we would get spikes — 1,000+ nanoseconds — and it was clearly the non-PTP-aware switch being unable to handle the network traffic from multiple sources.”
“With the Artel Quarra,” adds Rowell, “the clocking is significantly more stable and the drift is reduced to around 15-45 nanoseconds, well within tolerance for a RAVENNA-based system. If I see clocking spikes now, I know it’s not a switch issue.”
Gaining Time for Creative Considerations
With the reliability and stability of the switch preventing issues during setup, Rowell has found he has more time to focus on other aspects of a recording project. Factors such as the placement of microphones and musicians have become particularly important now that both performers and technical crew must follow social distancing guidelines due to coronavirus.
“All I have to do is plug the interfaces in, turn on the Quarra, and away it goes!” he says. “This means that I can concentrate on where musicians are going to sit or stand. In a funny sort of way, social distancing has forced us to relearn how to record various ensembles. We’ve all recorded large string orchestras before, but now all of a sudden, they’re occupying a space four times the size. Everything sounds a lot more distant, and the strains on the recording systems are far greater. It’s really nice not to have to worry about any of the technical aspects.”
In some cases, recording sessions involve multiple control rooms, plus a studio, listen-back facilities in the studio for the artists, and then a separate listening position in the studio for the producer — all to accommodate and maintain appropriate distancing. All of these extra signals are run over RAVENNA and through the Quarra switch. Again, Rowell is confident that as a PTP-aware system, the Quarra switch will sort out both the paths and the communications with ease.
“In terms of technical abilities, the Artel Quarra just covers all the bases, whether for a massive job or a smaller gig,” says Rowell. “While using the Quarra hasn’t changed how I engineer things, it does mean I don’t have to worry if the channel count goes up. Sometimes colleagues will ask me, ‘Why do you need 70-odd microphones to do some of these recording projects?’ My response is that I like knowing that I have options. The same is true for working with the Quarra switch. I know that whatever job comes in, the switch will be able to deal with anything I throw at it.”