In this issue of audio-visual strategy, we continue to bring you relevant content on the selection of TV sound speakers. In the following pages, we will start from the front end of the TV sound system, the audio output device.
The main purpose of HIFI enthusiasts to set up a TV sound system is to improve the sound quality of the audio in the program when watching TV programs. To achieve this, we want to use as high quality audio stream as possible. The output of the audio information stream depends on the audio output interface, and choosing a different audio output interface or output method will bring a completely different listening experience. Generally speaking, in the TV sound system, there are usually two options for the audio output device we connect:
The TV itself
Let’s take a look at the impact of connecting these two types of devices on the system we have built. If you choose to connect to the audio output port equipped with the TV itself, after we build a complete TV sound system, there is no need to change the wiring of the system again.
This is because when the power switch of the TV is turned on, no matter what playback device is used to output audio and video streams to the TV, these signals will be adopted by the TV, and the audio signals in the signal source will be processed by the TV. The circuit is redirected to each audio output port equipped with the TV for final output of the audio signal.
This is a one-and-done connection method. After using this connection method to set up a TV sound system, switching playback devices will be relatively simple. For example, when you want to watch IPTV, you only need to change the source of the TV to the HDMI interface corresponding to the TV set-top box, and the audio output port of the TV will automatically switch the audio source; if you suddenly want to watch the Blu-ray of the Blu-ray player DVD, just change the source of the TV to the HDMI interface corresponding to the Blu-ray player.
Therefore, this audio source connection method is very suitable for HIFI enthusiasts who are unlikely to make secondary changes to the entire TV sound system in the future. Even if you want to add another playback device again, you only need to connect the playback device itself to the TV, and the connection part of the audio output does not need to be changed again.
Although such a connection method is more convenient, it also has some disadvantages. Since the audio output from the original playback device will be processed by the audio processing circuit of the TV, it is difficult to guarantee whether the original audio signal has been changed or compressed when passing through these special circuits. The audio processing circuit of each TV is different. To be clear about this, it is necessary to read the manual of the TV in detail to be sure. But unfortunately, not all TV manuals will explain in detail whether the internal audio circuit corresponding to the audio output port has changed the original audio signal. This is a very uncomfortable thing for many HIFI enthusiasts. After all, when we encounter this situation, we always hope to get the exact technical information.
Program playback device
In the second connection, we use the program playback device as the audio output device. This connection method is suitable for friends who only watch a single program source. For example, if the TV is only connected to a single IPTV set-top box to watch TV programs, then you can choose to connect the sound system to the audio output port of the IPTV set-top box.
If you want to increase the program source of the TV in the future and connect other player devices, then you need to unplug the audio cable connected to the original playback device and connect it to the new player device again. This method is relatively cumbersome, and one thing that needs special attention is that the type and number of integrated audio output ports of different program playback devices are different. This means that when HIFI enthusiasts connect a new player device, there is a high probability that they will need to purchase a new audio cable.
Some HIFI enthusiasts will ask, isn’t the first connection method once and for all? Who will use the second connection?
As we said when we introduced the first connection method of audio source equipment, the main purpose of adopting the second connection method is to confirm that the original audio signal is completely transmitted to the active speaker or power amplifier. Avoiding the possible loss of sound quality is the wish of every HIFI enthusiast. Once the number of devices passing through the audio signal increases, the way each device processes the audio stream is opaque, which significantly increases the possibility that the audio information stream may be polluted. Therefore, HIFI enthusiasts who want to preserve the audio quality to the greatest extent still need to carefully and flexibly choose the connected audio output device according to the actual situation when building a sound system.
Unexpected situations that may occur
When connecting audio output devices, sometimes unexpected things happen. For example, after using the HDMI interface of some models of IPTV set-top boxes as the audio source output port to connect to the power amplifier or the TV itself. In the actual audition process found a rather special phenomenon.
If the HDMI output port of the IPTV set-top box is directly connected to the HDMI IN port of the TV, and then the Audio Out port of the TV is connected to the power amplifier device, the sound quality is obviously very poor. There is no obvious difference from the speaker effect that comes with the TV.
In order to determine whether the audio processing circuit of the TV has tampered with the audio signal. I also directly connected the HDMI output port of the IPTV to the power amplifier device. In the end, it was found that the same result was found, and the sound quality was obviously damaged.
This is inconsistent with the theory. The TV sound box uses a relatively large bass sound unit, and the matching power amplifier can also provide sufficient power as a support. Why is the final sound noticeably compromised and not much improved over the TV’s built-in speakers?
After several investigations, it was found that the audio signal output by the HDMI output port of the IPTV set-top box was obviously compressed. I don’t know whether it was intentional by the designer of the IPTV set-top box or a system bug.
In order to verify this conclusion again, I connected the independent analog audio output port of the IPTV set-top box as the audio source output port to the power amplifier to see if the sound quality has been improved. As a result, the entire TV sound system finally played its due role. This also confirms that there are certain “pitfalls” in some program playback equipment. If the TV sound system does not work well, it is not necessarily the “pot” of the TV audio processing circuit.
In order to prevent all HIFI enthusiasts from continuing to step on the pit, here is also the specific model of the IPTV set-top box that was found to have this defect at that time - the white Skyworth Skyworth IPTV 4K set-top box presented by China Telecom.
In recent years, many telecom IPTV users in major cities should have obtained this model. But it is not clear whether there is a difference between different batches and different software and hardware versions. You can verify it when you actually set up a TV sound system. If the sound source signal is compressed, the sense of hearing is very obvious. But the premise is that there is a sound system. If you use the speakers that come with the TV, it may not be very obvious.