by Bob Kirschner
During COVID lockdown, we are all learning to work at home - we need to accomplish at home all the important things that we used to do at our studios. Remote Voice Recording services have always been crucial for post production studios, but have now become essential for working from home. In my last blog post I summarized the seven most common remote platforms used by post professionals, and I grouped them into three broad categories based on audio quality. Today I’ll dive deeper, and compare and contrast the features of these platforms within each category, which I believe is a very effective way to make a realistic quality comparison.
I’ll start by listing the seven remote technologies grouped into my three categories:
Group 1 - Highest Audio Quality
ISDN
Source Connect
Group 2 - Very Good Quality (Google OPUS codec)
Source Connect Now
ipDTL
Session Link Pro
Group 3 - Acceptable Quality (standard audio over IP)
Skype
Uberconference
Comparison Notes
So what features will I be discussing to compare these remote technologoes? The most important feature that determines audio quality is the transmission codec. A codec is the algorithm, or computer code, that serves as the means by which the audio is compressed for transmission. This audio compression has a direct impact on the quality of the audio transmission. Audio codecs are described by their type (e.g. MPEG2 or G.722 within ISDN) and their bit rate (e.g. 128Kbps or 256 Kbps). Different codec types are not easily comparable without knowing what they sound like. But the higher the bit rate, the better the quality. Be aware, all technologies will show a transmission bit rate, but the bit rate number on it’s own does not tell you how good the codec sounds. Codec compression is a complex thing!
Other things that are useful to compare are service cost, latency time, connectivity requirements, maximum number of connected parties, and recording and playback features.
Group 1 Comparison - ISDN & Source Connect
This first group includes what I believe are the two highest quality remote audio technologies - ISDN and Source Connect. But, these are totally different technologies which makes it difficult to compare. It’s like having a beautiful Fuji apple and a tasty California orange and trying to compare the flavors - both are excellent! Additionally, ISDN is a telephone-land-line based platform that historically was the only game in town for decades, but now is being phased out by communication companies worldwide. But since ISDN is still being used, I feel it’s important to discuss.
ISDN is a broadcast quality service that supports multiple codecs, such as MPEG2, MPEG4, and G.722. The codecs are included in a proprietary (and expensive) hardware interface, examples of which are Telos Zephyr, APT and CDQ Prima. The highest bit rate for ISDN is 128Kbps for mono signals, and 64Kbps for stereo signals. ISDN always connects two parties, and both parties need to have the same matching codec on their end in order to make a connection. As well, each party must have ISDN service - an expensive service installed by their telephone provider. Needless to say, ISDN is an expensive option. One super-positive aspect of ISDN is practically zero audio latency since ISDN runs over copper lines. But since ISDN requires copper lines and can’t work over fiber, our industry won’t be using ISDN much longer.
Source Connect is software developed by Source Elements, a long-established pro audio company. They offer a range of software solutions, but I’m focussing on their three versions of Source Connect: Standard, Pro and Pro X. Source Connect uses the AAC codec, a very good sounding compression scheme that was originally designed to replace the old and not very good MP3 compression. Bit rates range from 192Kbps up to a whopping 1344Kbps - rates considerably higher than ISDN. The Standard version connects two parties over one or two channels, while the higher-level versions connect multiple parties using up to eight audio channels simultaneously. This is serious connectivity! Source Connect will work as a plug-in directly in your DAW of choice. Other great features include built-in RTS timecode sync, auto-restore to solve for dropouts, and ISDN bridging.
Perpetual license costs are $650, $1,450 and $2,490 respectively, and they offer monthly subscriptions as an option. All connected parties must own their own Source Connect license in order to connect. On the downside, installation and setup are technically challenging. And as far as latency goes, Source Connect does introduce a noticeable audio delay that can make communication a bit awkward at times. But without a doubt Source Connect offers the best audio transmission quality when compared to any other platform.
So that wraps up my ‘Group 1’ comparison. For my next post I’ll compare the features of Source Connect Now, ipDTL, and Session Link Pro. Stay tuned!