Complete Guide to Develop Audio Pipeline for Home Theatre & AV Receiver

Date: June 27, 2021

Author: Kajal Mishra

AV receivers are the hub of Home theatre systems.

In the hard times of COVID-19 pandemic, people are advised to stay at home and the only way to prevent the virus from spreading. Lockdowns are forcing people to be confined to their homes, and our social lives have moved online now. Netflix, Prime video, and other OTT platforms are witnessing significant growth and people have brought cinema to their rooms. 

The virus outbreak has propelled people to spend quality time with their families, to entertain them, and thus, increased the demand for home entertainment systems. Now, the situation is that most of us want to have our home theatre setup to enjoy the movies/ games/ music, and temporarily escape from the sense of uncertainty.

Do you know, how much time and effort it takes to build & design a home theatre system that caters to your needs. But, first how much you are technically inclined to know every detail about their audio pipeline development, connectivity, and functions of various latest sound formats like Dolby & DTS?

If you are interested in knowing the complete DSP software solution for a high-end Home Theatre System and Audio/Video receiver, then let’s dig into it.

Integration of Audio Codecs in Next-generation SoCs

As the consumer devices such as Home Theatres, Audio/Video Receivers, Media Players continue to expand and incorporate newer technologies, the system-on-chips (SoCs) designed for them become more complex. These SoCs must support the latest codec formats, multi-channel audio, high-tech audio compression formats, higher sampling rates, and advanced audio post-processing modules. 

In audio digital signal processing (DSP), audio SoCs need to be seamlessly integrated with audio codecs to establish the connection between input & output devices. An audio codec consists of a variety of input & output drivers like line inputs, amplifiers, ADC & DAC channels, microphones, headphones, speakers as well as digital peripherals (e.g., I2S, S/PDIF).

Integration of audio codecs into next-gen SoCs is required to support the latest audio formats from Dolby, DTS & Auro.

High-quality audio needs larger space and a substantial amount of power. Silicon audio IPs are integrated and optimized for performing specific audio functions and to reduce the power, area, and cost. Traditionally, the integration of audio IPs has always been focused on hardware, but it is the “software aspect” that drives the system complexity. 

For any audio applications, the software stack needs to support the latest audio formats from Dolby, DTS & Auro. The software components like audio codecs or post-processing modules must be integrated into a media streaming framework and then into the application software running on the next-gen processor. 

Let’s discuss some of the popular audio codecs from Dolby & DTS which are used by latest AV Receivers/ Home Theatre Systems and have the potential to engulf you in an immersive surround sound listening space.

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Dolby & DTS Codecs: Dolby DD+, Dolby TrueHD, Dolby Atmos & DTS:X 

Dolby Digital Plus

Also known as Enhanced AC-3 and successor to Dolby Digital (AC-3). DD+ is a versatile and sophisticated multichannel audio technology designed for next-generation AV receivers & Home theatre systems. It can provide the double efficiency of Dolby Digital (AC-3) and surround sound even with limited bandwidth. 

Dolby Digital Plus supports low bitrates, more audio channels, less compression, highly flexible technology, and is widely used by streaming & broadcast providers (e.g., Netflix, Prime video) to deliver excellent high-definition sound. It offers up to 7.1 discrete channels of surround sound for HD DVD players, Blu-ray Disc players, and set-top boxes and ensures compatibility with existing home theatre receivers equipped with coaxial or optical digital audio inputs.

How latest Dolby & DTS surround sound formats are taking your Home theatre & AV receivers to the next-level?

Dolby TrueHD

Unlike other audio formats, Dolby TrueHD is a complete lossless audio codec that provides the most authentic surround sounds identical to the master recording. It supports up to 8-audio channels (up to 7.1) and is widely used by HD and UHD Blu-ray Discs and enables the maximum audio fidelity possible by these devices.

Along with Dolby Digital Plus and Dolby AC-4, Dolby TrueHD becomes the improvised version of Dolby Digital (AC-3) and supports all other new audio formats. It can provide up to 16-discrete audio channels and has the scope to expand as new formats need more audio channels in the near future.

Dolby Atmos & DTS:X

Both are object-based surround sound formats mainly invented for home cinema that supports 5.1 channel of audio and more which adds overhead sound effects to deliver sound with greater realism than older formats. Both formats require a compatible built-in processor that decodes both the formats and you are all set. 

Dolby Atmos requires at least one pair of height speakers whereas DTS:X doesn’t require any additional height speakers. DTS:X lets the receiver’s auto-calibration and object-based processors decide where to send signals and sound effects. It’s always a good idea to have a receiver that supports both Dolby Atmos & DTS:X formats to enjoy the widest variety of contents with the best surround sound available.

Key Functions of AV Receivers 

AV Receiver Bass Management

Bass management allows you to set up your speaker & home theatre system in an organized way. Incorrect bass management can result in distorted sound quality and can even damage the speakers in some cases. In modern home theatre systems, speakers are not designed in a way to handle deep bass, so it’s necessary to have at least one subwoofer. Using a subwoofer can provide deep bass and lower frequencies get routed to the subwoofer and higher frequencies to the speakers and let the speakers produce frequencies they were designed to, thus allowing you to play them louder with less distortion.

Multi-Zone AV Receiver

Multi-zone in an AV receiver sends the multiple source signals to the speakers or separate audio systems in different locations at a time. It eliminates the hassle of connecting additional speakers and placing the speakers in another room.

For example, you can watch a movie on TV with surround sound in the main room while someone else can listen to a DVD player in another room at the same time. Both the devices are connected to the same receiver but controlled through separate remote-control options on the receiver. 

Object-based Rendering for Immersive Audio

Object-based renderers provide greater flexibility than channel-based audio as they deal with multiple separate audio objects. The object-oriented way is scalable because it doesn’t deal with a number of speakers in a room but only cares about the location & movement of the speaker. Only by changing the location of the object, we can get the sounds that we wanted, but it often requires a static sweet spot. These objects could be anything that helps to create a piece of content such as audio, video, sound effect, caption, etc and become an object when they are accompanied by metadata.

Both Dolby Atmos and DTS:X use object-based rendering to spot sounds’ locations within the room. In Dolby Atmos, every sound signal exists as an independent audio object regardless of no. of channels. These objects can be placed anywhere in the room and remain fully adjustable on the consumer’s end based on their listening environment to immerse them in sound.

DDR Tuning, Calibration & Testing

Double data rate (DDR) transfers the data twice per clock cycle i.e., on both the leading and falling edge of the clock signal that regulates it. DDR became quickly became popular as it used low power, double transfer rate, and was cheaper than earlier versions. It is the advanced version of Synchronous Dynamic Random Access Memory (SDRAM) which would fetch data only once per clock cycle. Over the years, it has evolved from DDR to DDR2, DDR3, and now DDR4 SDRAM and these upgraded versions require low supply voltages and save power.

Sometimes unstable memories cause intermittent failures in the systems and to minimize the risk, DDR memory has to go through the tuning & testing process. A product may have several read or write delays and that’s where DDR tuning is necessary. These delays should also be tested under a range of operating conditions such as varying temperatures. Using a software test, you need to ensure that the performance of the DDR memory is fast enough to run the software in your system properly.

Understanding HDMI ARC and eARC: Taking your audio to the next level

Movie buffs always get stumped when they have to choose between Audio Return Channel (ARC)and Enhanced Audio Return Channel (eARC). In addition to HDMI, eARC is an advanced version of ARC. HDMI has been able to eliminate the cable clutter and enhanced the user experiences when it comes to the use of Home theatre systems or receivers through a single HDMI cable.

In the ARC setup, the information transfer between source and receiver happens both ways (back & forth) unlike in basic HDMI where it happens only one way. In the case of TV & Receiver, both devices send audio-visual signals to each other, creating a two-fold channel for information using a single remote.

However, HDMI ARC has some limitations too which results in limited bandwidth for the signals. Advanced audio format like Dolby Atmos is not supported with this standard as ARC only deals with lossy compression formats with lower bitrates. Dolby Atmos can only be sent over HDMI ARC when the device is also compatible with Dolby Digital Plus.

To counter this limitation, eARC steps in to provide higher bandwidth and supports the multi-channel surround sound formats like Dolby Atmos, DTS:X, Dolby TrueHD, and much more. Some other benefits of using eARC include improved audio and video sync even when multiple devices and formats are used at the source & receiver end and provide a surreal experience to the viewers.

The Bottom Line

The digital media industry has come a long way from providing analog audio to immersive sound experiences. The deployment of Dolby & DTS sounds has completely shaken the world of cinema with its outstanding audio quality. People are opting for surround sound-enabled home theatre and AV receiver systems which have propelled the companies to upgrade their software solutions regularly and get adapted to these changes.

We, at PathPartner, provides the complete audio pipeline development solutions as a ready-to-integrate SDK for your Home theatre systems/ AV receivers/ Soundbars on next-gen SoCs from various Tier-1’s. If your product requirements match with our offerings and it makes you curious to know more about us, please write to us at marcom@pathpartnertech.com 

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