Party Qingkun
    TI Senior Simulation Application Engineer
    With 14 years of industry experience, we focus on audio product and system design. As a senior analog application engineer at TI, we analyze the new technologies and the most popular audio solutions in the field of audio chips for you.

Before starting to answer the questions from netizens, I'll first summarize two frequently mentioned questions:
1）Which indicators should be given priority when choosing a plan?
2）What are the current mainstream usage solutions for Bluetooth speakers?
Ⅰ、Which indicators should be paid attention to?
    Simply put, since Bluetooth speakers are relatively small, the requirements are not very high. What needs to be paid attention to are the most basic audio indicators, such as power, efficiency, frequency response and distortion.
    Other aspects include the battery's playback duration and charging speed. When it comes to end customers, more vivid indicators are often needed to describe it, such as the applicable space or the distance at which it can be heard. Other effects mainly lie in subjective evaluation. Few products use their objective indicators as promotional points to inform end users. So the very low-end and low-priced Bluetooth speakers on the market only care about power. In layman's terms, this kind of speaker is just for "making a sound". The indicators that affect the listening experience and usage experience are generally not measured.
    Products that pursue quality all ensure design and quality control for the basic indicators that affect sound and battery life. Moreover, the indicators are also relatively static figures because the test signals are relatively stable, while music and audio are complex changes and large dynamics. Therefore, the same indicators do not necessarily mean the same subjective performance. It can only be said that objective indicators are the foundation. These indicators are sometimes mutually restrictive, so generally, one should choose the appropriate chip and design based on the characteristics of the product they need.

Ⅱ、What are the mainstream Bluetooth speaker solutions?
    For the mainstream Bluetooth speaker solutions, the power of a general Bluetooth speaker is usually less than 10W, typically ranging from 3 to 6W.
The low-power mono Bluetooth speaker mainly uses LM48511, which has a built-in boost section. With a 4-ohm speaker, it can reach 5.4W 1% THD+n. Because it is an H-class power amplifier (that is, the boost voltage of the power amplifier will be adjusted according to the input signal), its efficiency is very high.
For medium and high-power Bluetooth speakers, such as 5W to 10W, mono or dual-channel ones, TPA3130D2, TPA3118D2, and TPA3128D2 are generally used as power amplifiers, while PCM5121 is typically used for DAC and processing. PCM5101 or TLV320AIC3254. Both PCM5121 and TLV320AIC3254 have miniDSP inside, which can perform some sound processing, including basic EQ, etc.
The performance of these power amplifiers is all very good. Because they are closed-loop feedback, the TPA3130D2 is in QFN packaging and has a relatively small volume. The TPA3128 is in hybrid output mode and has a very small quistatic current, which helps to improve system efficiency. The TPA3130D2 is a dual-channel amplifier with a power output of 15W per channel, while the TPA3118D2/TPA3128D2 are dual-channel amplifiers with a power output of 30W per channel. Therefore, both have very low internal resistances.
Digital input power amplifiers are also widely used and have more advanced audio processing.
Digital input power amplifiers for ordinary sound processing generally have functions such as multi-band EQ (5 bands to 10 bands), 1 to 3 bands DRC (segmented by frequency), and distortion control. The commonly used Bluetooth speakers include TAS5711, which supports 2.1 output combinations, and TAS5709/TAS5715, which support 2-band DRC, etc.
There are also some digital input power amplifiers with more powerful sound processing capabilities, featuring built-in miniDSP and RAM/ROM, such as TAS5756M/TAS5754M. We offer some pre-made processing flows for selection and use, such as up to 10 EQ segments, multi-segment DRC with enhanced functions, and bass enhancement. Adaptive EQ, etc. And the voice of the more advanced processing, it is "smart power amplifier", such as TAS5766M/TAS5782M/TAS2557M, this algorithm to modeling of horn, play music, the status of the real-time prediction horn, to control the vibration amplitude, and the temperature in real time, avoid the damage of horn, on this basis, The instantaneous power of the speaker can easily reach more than three times the rated power. The greater the power of the speaker, the greater the power that can be achieved at the peak in a short time. This can achieve a very good bass effect and higher loudness that cannot be achieved by the traditional algorithm, making up for the shortcomings of small-diameter speakers and small sound cavities.
In addition, we have newly launched some digital input power amplifiers with higher performance ratios, such as TAS5733L and TAS5753MD, featuring 15 EQ segments and 3 AGL segments. We will also introduce products that do not require output inductors in the future.
The EQ here is actually a BiQuad filter, which can not only be used for EQ, but also for high-pass, low-pass, Notch, Bass/Treble shelf and other filters.
The software tools are moving towards a high degree of unification. Once you are familiar with the use of one power amplifier, you can quickly get started with the use and debugging of other power amplifiers. It is convenient for rapid productization to shorten the development time, and at the same time, it reduces the chance of errors while timely using new products and new technologies.
2.1. Question: To achieve a five-minute charge and two-hour music listening experience in a dual-speaker Bluetooth system, what is the minimum charging current required? (Set the battery of the Bluetooth speaker to 2200mA/7.4V)
    Answer: The battery capacity of a Bluetooth speaker is typically 7.4V*2200mA·h= 16,280mW ·h. Take a 10W Bluetooth speaker as an example. Its average power is about 1.5W, and its playback time T=16280mW·h/1.5W=10H.
    Therefore, the power consumption of two-hour music playback is W=1.5W*2H=3W·h. Therefore, 3Wh of energy needs to be charged within 5 minutes. Thus, its charging power should be P=3W·h/(5/60 h) =36W. Therefore, the charging current should be set as I=36W/7.4V=4.86A. TI's charging IC, the BQ24617/BQ25703A synchronous controller, can meet this requirement.
2.2. Question: What exactly makes the "audiophile operational amplifier" that audiophiles pursue so good? As far as I know, from the professional perspective of operational amplifiers, the technical indicators of operational amplifiers that are considered very good are not as good as those of some of the current excellent audio operational amplifiers. Are these "audiophile operational amplifiers" really that good? Or was it driven up by the market?
    Answer: Actually, there is a very important issue, which is subjectivity. People tend to prefer the sounds they often hear, especially when the differences are not significant. So when objective indicators reach a certain level, comparisons are often necessary. In addition, in terms of objective indicators, the measurement of indicators is relatively static, such as test signals with a fixed amplitude or a fixed frequency. It is different from the dynamics of music. The differences in harmonic components and very slight low noise can cause significant differences in subjective auditory perception. Harmonics are related to circuit structure and manufacturing process. It is also closely related to power supply and peripheral circuit design. TI also has many new and excellent audio operational amplifiers, such as the OPA728.
2.3. Question: Could you recommend some noise reduction solutions for audio?
    Answer: the resident of noise, such as wind \ the road noise can use the built-in TLV320AIC3254 / TLV320AIC3256 / TLV320AIC3262 DSP codec to deal with. The ANC is not officially supported now.
2.4. Question: Why do many smart products nowadays use 2.4GHz module chips for signal transmission? What are its advantages? Are there no other frequency bands that can be used as substitutes?
    Answer: Civilian free band is easy to implement and has a low cost. 5G is another frequency band that has begun to be widely used at present.
2.5. Q: In the design of Bluetooth speakers, how to choose the appropriate charging chip and DC chip to avoid PA overcurrent power-off protection?
    Answer: The kind you mentioned is mainly caused by insufficient power supply carrying capacity or insufficient transient response. Therefore, sufficient margin should be designed during the design process. Also, use the PLIMIT function of the power amplifier.
2.6. Q: Nowadays, many audio systems are striving for smaller size and better sound quality. Are there any good designs or recommendations in this regard? Which chip from TI can improve the sound quality and stability?
    Answer: The main recommendations are TAS5782M and TAS2557.
2.7. Q: How many CoDECs are needed for voice recognition in smart applications such as smart speakers and TVS? What is the model of codec? How many MIC channels are needed?
    Answer: 2 to 4 TLV320ADC3101 tablets. It is generally 4 to 8 channels of MIC.
2.8. Question: What are the requirements for the speaker of TAS5782M?
    Answer: If intelligent algorithms are used, it is generally 3 to 8 ohms and the power is over 1W.
2.9. Question: Does TI have a mature multi-MIC voice acquisition and pre-processing solution for voice recognition in smart speakers?
    Answer: It is recommended to use TLV320ADC3101 or PCM1864, and the DA10xx chip for noise reduction and array algorithms.
2.10. Q: Which amplifier is used for the wireless headphones? How about the battery life?
    Answer: It is recommended to use TPA6141A2. In terms of efficiency, it is at a very high level. The battery life mainly depends on the size of the battery and the headphones.
2.11. Q: What solutions have been adopted for battery management in wireless headphones?
    Answer: It is recommended to use BQ21040 and BQ24040.
2.12. Which of TI's 20W two-input and one-output power amplifiers is currently more commonly used?
    Answer: TPA3136D2 is recommended.
2.13. Q: If the Soundbar and power bank functions are combined, does TI have a similar solution?
    Answer: Actually, the overall solution that is directly used by TI is still relatively rare, but it can be combined for use. Generally, Bluetooth speakers are combined with power banks. Soundbar is not convenient to carry because of its large size. To achieve a better Bluetooth speaker effect, you can use the TAS5782M chip with a special algorithm.
2.14. Q: How many types of inputs does the Soundbar support?
    Answer: Generally speaking, among HDMI, Bluetooth, optical fiber, coaxial, analog, and 3.5mm analog, some support USB playback.
2.15. Q: How is the switching frequency set for TPA3136D2? How is closed-loop feedback designed?
    Answer: 50k, so generally there is no need to consider adjusting the frequency as it is less likely to interfere with am. The chip itself is a closed-loop feedback. If you want feedback after filtering, you can change it to LC filtering and then add feedback. Generally, this is not necessary.
2.16. Q: How can the sound quality of audio signals transmitted wirelessly be optimized?
    Answer: Transmission software often has little room for modification as it is provided by chip manufacturers. So what you can do might be to optimize the antenna design, reduce noise and enhance sensitivity. In addition, it is also necessary to check the sound quality of the power amplifier section to determine which part generates more noise.
2.17. Q: I always hear that the sound quality of Bluetooth speakers is not particularly good. Is it due to the rate limit of Bluetooth communication, encoding and decoding issues, or some problems with the output of the DA and the design of the power amplifier at the back?
    Answer: It is mainly caused by the relatively popular low-end products in China. Since costs need to be saved from beginning to end, there will always be some problems, and the sound quality cannot be done well. It's just cheap. Some brands perform better but have a relatively high brand premium.
2.18. Q: How to ensure that the signal is not interrupted and improve stability when transmitting via Bluetooth? Is the general transmission distance of Bluetooth about 10 meters?
    Answer: It's around 10 meters. It will be better after version 5.0. Generally, if there's no problem with the software, it mainly depends on the hardware to improve the sensitivity.
2.19. Q: How far can the built-in wireless transmitter of the Soundbar go?
    Answer: It is generally within 20 meters. Since it is 2.4G, it needs to be retransmitted when someone blocks it.
2.20. Q: When conducting speech recognition, is it necessary to be connected to the Internet? Can offline data be used? Is there a better solution from TI?
    Answer: Internet connection is required. The advantage of the TI solution is that it provides a certain degree of localized speech recognition. Therefore, some commands do not need to be connected to the Internet, and some basic operations can still be completed when there is no Internet connection.