Parikh, Harris Intraplex System Architect and Software Lead. ‘Because the algorithms are more or less
standard, the differentiation of products comes from being able to adapt to IP
Radio World asked
several codec suppliers about trends in their area of expertise and we got back
some great information. Here, we talk with Keyur Parikh, Harris Intraplex system architect and software lead. This is one in a series.
Let’s say I’m an
engineer but I’ve been out of the market for several years. What’s the most
notable way that codecs are different now?
Parikh: A major difference is the transport model. Circuit-based networks with
high recurring costs are now being replaced with lower-cost ubiquitous IP
networks (both wired and wireless). In fact, it is not uncommon for users to
have access to multiple IP paths connecting the transmit end to the receiver
for resiliency. Another trend is the use of newer algorithms such as the AAC
family of codecs, which can provide near-linear quality using a fraction of
bandwidth used by linear PCM.
direction is codec design heading?
Parikh: Increasing processor speeds have allowed codecs to be implemented in
software. The software implementation has enabled flexibility in
reconfiguration of codec algorithms on the fly as well as integrating IP
networking features. As codecs increasingly become IP-based, inter-operable
standards for real-time and Web streaming are becoming prevalent. EBU has put
out a standard that is based on RTP streaming for interoperability. By adapting
protocols such as Shoutcast and the ability to stream using Shoutcast as well
as RTP for broadcasting, codecs are extending their real-time broadcasting
reach to PCs and smartphones as well.
What’s your take
on Internet reliability for mission-critical transport?
Parikh: Internet comes in many flavors: from a managed IP service to
unmanaged public Internet. Managed service can provide reliable/deterministic
service (almost like a circuit service). With public Internet, there are no
guarantees on the quality of service. A user is still leery of the Internet,
but a well-designed codec in today’s market will provide multiple tools in its
networking features kit to combat impairments in the IP networks. These tools
include, but are not limited to, interfaces for multiple IP paths to be used
simultaneously, forward error correction and advanced features which can
provide hitless protection switching. All of the above enable the user to
achieve the reliability of a circuit connection with a lot less recurring cost.
“state of the art” in bitrates and algorithms?
Parikh: For musical content, the AAC codecs are state of the art these days.
AAC-HEv2 can achieve 90 percent of linear quality at 64 kbps. HE and HEv2 are
specified in various broadcast standards such as XM Radio, Mobile Handheld,
DAB+, DRM. On consumer side, Apple’s iTunes also uses AAC as its default
codec. AAC also has a low-delay option, however for some user scenarios,
this is still not low enough and therefore users would have to consider other
options such as linear or APT codec. For wideband voice, G722 is still a very
good option. It is low-delay and royalty-free.
What is the next
big challenge for codec designers?
Parikh: The challenge for codec designers is to create network adaptable
systems. Because IP networks come in various qualities, the codec needs to be
able to tailor its transmission and algorithm for each path simultaneously. For
example, when content is to be sent to multiple receivers over different IP
networks simultaneously, the codec needs to use the optimal algorithm for each
receiver. Receivers with high-speed connections may be sent uncompressed
content, while ones with lower bandwidth and reliability should be sent content
with appropriate compression and with network layer reliability features
should a smart buyer of codecs be asking?
Parikh: Because the algorithms are more or less standard, the differentiation
of products comes from being able to adapt to IP networks. Specifically, the
ability to simultaneously encode the same content with different algorithms and
bitrates with different network layer reliability handling is a key. Having
multiple interfaces and providing “hitless” operation using them is important.
Providing advanced features which can send multiple copies of the same packets
in a time-dispersed manner and intelligently resequence them at the receiver is
key to combating packet erasure. RTP level forward error correction is another
technique that is used to recover lost packets.
What is your
newest or most notable codec product?
Parikh: The new Harris IP Link 100 and IP Link 200 Audio Codecs carry on the
Intraplex tradition of robust “Always On Audio” for STL and high-reliability
audio networking applications. The IP Link platform provides user-configurable
encoding options along with advanced capabilities for operation on managed or
unmanaged IP networks. Key features include dual WAN interfaces for
streaming over diverse networks; simultaneous multi-coding of a single audio
source onto multiple streams with different algorithms and/or bitrates; and
Dynamic Stream Splicing for protection against packet loss and “hitless”
recovery of the audio stream.
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