TYPE-C headphones - farce or business opportunities?
Recently, the TYPE-C headphones on the rivers and lakes rumors of fire, rampant. Coupled with music as a CDLA industry alliance again, and echoes. Let a lot of friends in the industry, want to come together to ask what. Xiao Bian early in the signal conversion chip design, trying to grasp the limited information from their own interpretation to the friends about the truth behind the TYPE-C headphones. Knowledge, error is inevitable, please correct me.
First, USB-IF definition of USB TYPE-C headphones
Since it is a USB TYPE-C headset, it should first consider what the USB-IF said. From the USB TYPE-C SPEC 1.2 document, we can see, USB-IF in order to 3.5mm headphone jack compatible, took a lot of effort, directly to the TYPE-C analog headphones defined in the CC LOGIC level. In the CC LOGIC state machine definition, USB-IF to compatible TYPE-C analog headset, the state transition picture with the same spider web. Pin definition, in order to be compatible with the negative level audio signal output, but also painstakingly. Finally, the pin out as follows:
Can be seen from the figure, TYPE-C headphones, the simplest approach is to directly CC and VCONN are grounded. Then the original USB2.0 data transmission line, respectively, as the left channel and right channel. SBU1 and SBU2, as a microphone signal. Therefore, USB-IF defined TYPE-C headphones, the above does not require any chip, or resistors and capacitors. Here, some people will drop Pakistan, and do not chip and RC ... .... That is not blind nonsense it? Yes, not only that, in this mode, the headset can also charge through the VBUS to the reverse charge 500mA of power. As a result, while charging, while listening to music, feeling very High. Therefore, TYPE-C headset fried hot part of which is blind nonsense.
The above is a USB-IF definition of an analog TYPE-C headset. So USB-IF digital headset is not defined it? There is indeed a word, this sentence is to say:
Appendix C USB type-C digital audio:
This appendix is reserved for the future definition of the USB Type-C Digital Audio support.(简单翻译一下，就是“以后再说”。)
Second, the music as the CDLA and digital audio TYPE-C headphones
USB-IF, why will "later say", rather than as music as to mention a standard out? The main reason is "a bit redundant." Digital audio technology in fact a long time, some audio enthusiasts in the PC era, in fact, played a high-fidelity USB sound card, or called HIFI fever USB external sound card, Taobao search can find a lot. Never played a friend will feel very strange, the computer integrated with a good built-in sound card, how there is a group of people like to toss it? One of the mysteries, lies in the sound quality. Original computer sound card is aimed at the public user, DAC output is 16 bits, the sampling frequency is generally between 22k to 48k. For most people's ears, this is enough. However, there are so some people, they have the ultimate pursuit of music effects, I hope to hear the sound of nature. Feel that the existing sound card is far from being able to meet their requirements. As a result, higher output accuracy and output speed of the USB external sound card appeared, the accuracy of up to 24bit (not really able to do 24bit, but significantly improved than 16bit), the speed reached 192K. Facts have proved that this sounds of nature, can touch the hearts of fans in the soul of a string, which was loved. However, PC for songs, is not a good choice, so, in the PC era, high-fidelity external sound card, there is no real pop up. The Music CDLA is essentially the PC era of practice, extended to the mobile phone era, and the external sound card module size, reduced to only USB plug size, making high-fidelity sound quality, can really spread to every consumer, which is A very valuable thing. Here, let us look at the audio transmission path, in the traditional way and CDLA way difference:
Figure 1 analog TYPE-C headset audio transmission channel
Figure 1 for the traditional analog TYPE-C headset music transmission channel, the red part of the sound quality loss, for domestic android phones, the built-in DAC has been the main sound quality caused the loss. And before entering the TYPE-C port, there is an analog switch used to switch the audio mode or digital mode, and then through the TYPE-C interface, and then through the headphone cable, sent to the left and right speakers. Among them, the most important sound loss in the DAC part, the other part, but theoretically there is loss, may not really loss of hearing effects.
Figure 2 CDLA TYPE-C headset audio transmission channel
Figure 2 for the CDLA TYPE-C headset audio transmission channel, the DAC on the external USB plug, so no longer need the internal Switch, sound quality loss exists only in the headset line. Of course, this is a simple schematic, in fact, from the decoder to the DAC between the USB2.0 format is transmitted, but this part of the pure digital transmission is 100% fidelity, you can ignore.
Figure 3 ideal non-destructive transmission path
Figure 3 is the ideal audio transmission path, before arriving at the speaker, all for the digital signal transmission 100% fidelity, DAC and speakers integrated together. The output of the DAC is buffered and drives the speaker directly. Between the two sides of the DAC, you can use a digital signal to the data synchronization. This is true of the whole non-destructive transmission.
Of course, personally think that these practices, not necessarily the ultimate form of TYPE-C headphones. As a music player to do the Apple, personally feel his TYPE-C headphones should be like this:
Figure 4 guess APPLE TYPE-C headphones
Figure 4 is Xiaobian guess APPLE TYPE-C headphones, does not require any components, pure analog headphones. The reason for this is that the loss of sound quality on the interface and the cable can be reduced by good design. CDLA, the most core value, in the final analysis, or to solve the domestic mobile phone audio output performance, but off the problem.
Third, the use of headphones when the phone charging problem
According to USB-IF specification, analog headphones as long as the external VBUS power over, you can 500mA charge. However, this current is far from enough to meet the current mobile phone charging needs. For digital headphones such as CDLA, the benefits are achieved while listening to music, while fast charging. Only need to add a USB PD controller such as LDR6023, and the addition of a USB TYPE-C of the mother of the adapter as an access port, on it.
Figure 5, while charging while listening to music applications
Summary As can be seen above, TYPE-C headset fire up, half of the nonsense, the other half is business opportunities. Opportunity lies in two parts, one is the realization of high-fidelity sound, such as CDLA, the other part is the integration of charging and headset functions. Hope that the industry friends to seriously consider their own advantages in resources, targeted, do not blindly follow the trend. Of course, limited to personal vision, there may be more business opportunities, I did not recognize.
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