Home theaters cannot just talk about picture quality and ignore sound effects. It is difficult to match the exquisite picture only with the number and volume of speakers of the TV. Traditional home theaters use AV Receiver with multi-channel passive speakers on audiovisual equipment and More than one subwoofer. Still, this combination will bring a lot of trouble in wiring and speaker positioning. So the SoundBar has become the first choice for users who do not want to toss and want to experience surround effects.
It is Enough to Spend Less Money
Let’s clarify one thing. The soundbar is a compromise with the living room space like laser TV. To achieve the same effect will definitely cost more money. Spending more money may not necessarily achieve better results, so It’s not worth wasting money to achieve the desired effect.
The audio track of a movie is not as rich in melody and overtones as in music. The dialogue and sound effects are all dry sounds. Therefore, in the case of a limited budget, don’t talk about the sound quality first. Fundamental factors such as the number of channels, power, and frequency response should be considered.
Typically, sound quality is proportional to power and price.
Common Multi-channel Audio Track Specifications and Interfaces Required
Dolby AC3 and DTS are surround sound encodings in the DVD era. DTS occupies a place with the advantage of its bit rate advantage. The AV receiver at that time uses optical fiber and coaxial transmission AC3 and DTS sources.
In the era of BD and HD DVD (2008), Dolby mixed the existing MLP (DVD-Audio audio track) encoding with Ac3 to become Dolby TrueHD. While achieving a lossless multi-channel surround soundtrack, it also retains compatibility. EAC3 has two-channel support capability. The bit rate is also higher, and there are more applications on the network.
DTS HDMA also includes the DTS core, which is lossless and backward compatible. With high-code wins, it is also the leader in the BD era. As for the lossy DTS HD is rare, but some Japanese animation Blu-ray will be used.
When Dolby launched Dolby Atoms, it changed the gameplay. No longer expanding the code rate or the number of channels. Dolby came up with “object-oriented audio”. But the sky channel is still expanded, allowing the horizontal sound field to expand in height.
This is because UHD discs need to reserve bandwidth for the video, and there is no way to allow the audio track to increase without limit. On the other hand, adding sound channels to increase sound localization seems backward in technology. The additional information inserted in the existing code is enough to express the occasional sounds in the film, such as thunder, plane takeoff, etc.
And Dolby Atoms is also based on EAC3 and TrueHD corresponding to the streaming media and UHD disc market, thus leading the Dolby Vision of HDR image technology.
DTS did not launch its own object-based audio technology until 2015, DTS: X, which is also based on DTS HDMA, adds the use of polar coordinates to restore object audio positioning information. Since Dolby Atmos has already occupied the market, DTS had to launch IMAX ENHANCED in conjunction with IMAX.
Although DTS claims to be easier to use for users and producers, looking at the overwhelming Dolby Vision + Dolby panoramic sound content, it seems that the outcome is fixed.
Therefore, the evolution path of the consumer-grade surround soundtrack is lossy, lossless, to object-oriented audio. To make it easier for everyone to understand, let me make an analogy:
- AC3 is a 128K MP3;
- DTS is 320K MP3;
- TrueHD is equivalent to 128KMP3 with APE;
- DTSHD is equivalent to 320KMP3 with FLAC;
- Object-oriented audio maybe a bunch of scattered wav + txt, and when to put which channel to put is determined by the program;
Many people think that Dolby atmos will have better sound quality. This may be a misunderstanding. It can only be said that the positioning information is richer. It is DTS HDMA and TrueHD that determine the sound quality. Lossless is always good, although most people may not hear the difference.
Fiber vs Coaxial
After the HDMI unified audio and video interface, the optical fiber and coaxial are gone. It’s just more common on some low-end products. However, because of its low price, it can transmit audio separately, and it has specific use-value. Especially common on TVs and soundbars. Because most models only support AC3 and DTS decoding.
With Bluetooth, WiFi, Airplay, and other functions, it is for connecting a mobile phone to stream music. It is not suitable for connecting to a TV, and it cannot transmit multi-channel audio source code.
Arc vs Earc
The role of ARC and eARC is when the TV itself is the signal source. You can use only one HDMI cable to transmit the signal back to the amplifier or soundbar.
The so-called ARC refers to “Audio Return Channel”, an additional function when the HDMI Forum proposed HDMI 1.4 in 2009. If both the TV and the AV receiver are equipped with HDMI1.4 terminals (or higher than HDM1.4 version), the sound can be sent back from the TV to the AV receiver or other audio equipment, so that the audio system can replace the TV speakers.
eARC is a new feature that was added when the HDMI Forum proposed HDMI 2.1 in 2017. Its full name is Enhanced AudioReturn Channel. Compared with the previous ARC technology, eARC has improved a lot. In terms of audio transmission capacity, the maximum data rate of eARC can reach about 37Mbps (ARC is only about 1 ~ 3Mbps), which is a growth of more than ten times. This allows eARC to transmit without Compressed 5.1 or 7.1 multi-channel audio (that is, Dolby True HD and DTS HD-MA), and can also transmit advanced “object-oriented audio”. That is Dolby Atmos and DTS: X.
In contrast, the old ARC only supports Dolby Digital, DTS, PCM 2.0, and other previous-generation sound formats, which no longer meet today’s needs. The birth of eARC also prompted Netflix to increase the proportion of Dolby Atmos sound effects when providing online movies.
Three: the role of different channels.
The Role of Multi-Channels
Compared to 2-channel stereo, how many channels can be called surround sound? The answer is 4 channels.
The earliest surround soundtrack is 4-channel. Left front (FL), right front (RL), left surround (SL), right surround (SR) is enough to surround the audience with the sound field. The center channel is not necessary. But if the room is large, the center channel can ensure that the vocal dialogue is clearer. If the budget is insufficient, removing the center channel will not hurt, because the center channel does not have much positioning information. This is 4.0 or 4.1 channels, and the first number represents the number of main channels.
Left-front FL, right-front RL, left-surround SL, right-surround SR, center channel plus bass channel, constitute the most prevalent 5.1 surround sound system. Of course, like a soundbar, it is not difficult to include a center channel. However, there are still many low-priced soundbars that cut off the center channel, and you need to pay attention when buying.
The 7.1 channel is the addition of the left and right channels. At this time, they are called left and right surround, and the original left and right surround at the back becomes the back surround. There is a high probability that the speakers on both sides will not be placed in many people’s living rooms, so I will not consider them for now. And if the sky channel is added, 9.1 channel decoding and amplifying ability are required. Ceiling speakers are more effective.
In high-end soundbar products, the “sound beam” concept is often adopted to achieve side surround, back surround, and sky sound channels through wall reflections. So there are 7.1.2 or even 7.1.4 products. Sky channel is a new vertical channel added by Dolby Atmos and DTS: X. The number of sky channels is after the second decimal point, 5.1.2 represents 2 sky channels, and 5.1.4 represents 4 sky channels.
After the first decimal point is the bass channel. If the primary channel speaker is not full-band, its low-frequency signal is reproduced through the subwoofer. This depends on the cutoff frequency set by the amplifier. The subwoofer complements the frequency response of the entire set of speakers. Generally, subwoofers start from 10 inches, and 12 inches are typical. 15 inches is not too big. Starting at 150W, two more are needed for balance. This becomes x.2.x in the speaker placement.
The Most Easily Achieved Speaker Layout: 5.1.2
Whether it is a traditional home theater system or a soundbar, the sky channel through the ceiling reflection or the physical surround speakers are the most straightforward layout to achieve. It is the minimum requirement to enjoy the original panoramic sound.
Of course, I personally think that the back surround realized by reflection is not very reliable. Originally the soundbar was lower under the TV. It was facing the sofa, and all the sounds were sucked away. It is difficult to achieve extremely important back surround positioning, which has a significant influence on the sound field. The reflective sky channel is better because the ceiling is smoother.
Regardless of whether the sound is output through an independent speaker or a reflective wall with built-in speakers, a channel requires a unique power amplifier circuit and speakers. Although the positioning effect of the reflection method is relatively weak, it is still considered a real channel.
Dolby Atmos Height Virtualizer and DTS Virtual: X
When the number of your audio channels is exactly the same as the audio track, perfect. But if the sound source is 2.0, you have 5.1 channel speakers, then you can use some virtual surround sound technology to generate fake surround sound, referred to as up-mix. Just like watching 4K TV with a 1080p source, an Upscale is required. There are many similar technologies, such as DOLBY Pro Logic II, DTS Neo6, DTS Neo: X.
And when the sound source is 7.1 channel, you only have 5.1, 2.1 channel speakers, you need to mix the original audio track into the speakers you own, referred to as down-mix, or simply called mix. But in fact, it is like Watching 4k video with 1080P TV and finally mixing the 7.1 audio track to 2 channel playback, in fact, there is no effect. Most people use stereo speakers/headphones to hear the sound of the film after downmixing, and no doubt, loses the sense of positioning and surrounding, but at least you hear all the sound.
If you don’t have a sky channel, and your soundbar supports Dolby Atmos Height Virtualizer or DTS Virtual: X, you can virtualize the vertical sound field through existing speakers.
Don’t expect these technologies to bring the effect of replacing physical speakers. Besides, Dolby, DTS, and other manufacturers have developed many virtual surround sound technologies for the computer and mobile terminals. I personally think that they can be regarded as enhanced versions of upmix and downmix technologies, which cannot truly achieve multi-channel surround sound field.
Of course, I’m not saying that these upmix and downmix, virtual surround technologies are useless, but if you want the effect, you must first ensure the physical channel.
Other Things to Note
Sound field calibration technology
The listening environment has a significant impact on multi-channel surround sound, and the AV receiver’s built-in sound field calibration function has almost become standard. Measuring the listening position data about the phase and frequency response through the microphone makes the overall sound field more balanced. For soundbar, this function represents professionalism.
What is the impact of supporting video formats?
Either the power amplifier or the soundbar. The high-end ones will be labeled like supporting 4K / 60p, supporting the terms HDR, HLG, Dolby Vision, BT2020. As a speaker, what’s the use of supporting these? The key lies in the transmission of audio and video signals by an HDMI cable. If these video specifications are not supported, it is highly likely that the video signal from the video source will not be delivered to the TV.
In traditional AV receivers, the video source is connected to HDMI IN, and the display device is connected to HDMI OUT. The power amplifier leaves the audio to decode, and the video is transmitted to the display device intact, so it must support the corresponding video protocol to connect successfully.
With soundbar, the channel effect is not as good as the 5.1.2 surround and 7.1.2 surround with actual speakers. But because the soundbar’s design is simple, it can be better integrated into the living room environment. For people who don’t have a big budget, or who like simple design, or who don’t have enough space and don’t want to put too many speakers, the soundbar is an excellent choice for sound equipment.