How to Test Bluetooth Devices 如何测量蓝牙音频设备

蓝牙协议是无线传输音乐和语音的标准协议。它能将音箱，耳机/耳麦等与手机，电脑，娱乐系统或车载音频系统连接。使用蓝牙协议的设备怎样确定音频品质呢？我们应该考虑哪些因素？

The Bluetooth standard defines different types of communication for different applications. These are called Bluetooth profiles. There are three relevant profiles for the transmission of audio signals:

A2DP

The Advanced Audio Distribution Profile is used to stream stereo signals in HiFi quality. The standard SBC Codec allows sampling rates up to 48 kHz. AAC or APTx codecs are used optionally.

蓝牙立体声音频传输规范用于传输高品质立体声。标准 SBC 编码可实现高达 48 kHz 采样率。另外还有 AAC 或 APTx 编码可选。

该规范规定了两个固定角色，Source（源）和Sink（接收方）。

 

There is an A2DP Source and an A2DP Sink profile.

• 典型 A2DP Source 有手机，平板，电视等；
• 典型 A2DP Sink 有音箱，耳机等。

HSP（HeadSet Profile）

蓝牙耳机规范用于双向语音传输。其中的 SCO 编码实现了 8 kHz 采样率，这个规格跟传统电话的指标对应。该规范中有 Gateway 和 Client 两个角色。

The HeadSet Profile is used for bi-directional voice transmission. The SCO Codec provides a sampling rate of 8 kHz. This corresponds to the bandwidth of a conventional telephone connection. There is a HSP Gateway and a HSP Client profile.

• 典型 HSP Gateway 有手机；
• 典型 HSP Client 有耳机等。

HFP

The HandsFree Profile is also used for bi-directional voice transmission, but offers some extended properties over the HSP profile. As examples, there is the possibility to transfer the address book of the gateway device to the client, and the MSBC codec provides a 16kHz sampling rate for improved speech quality (e.g. for Skype calls).
免手持设备规范同样用于双向语音传输，但比 HSP 规范提供了更多扩展属性。比如，可以将通讯录从 gateway 设备传输到 client 设备。其中的 MSBC 编码实现了 16 kHz 采样率，提高了语音质量。

A HFP Gateway and HFP Client is identified.

该规范同样有 Gateway 和 Client 两个角色。

• 典型 HFP Gateway 有手机，电脑；
• 典型 HFP Client 有耳机，汽车音响等。

许多设备都支持全部三种协议。它们会根据应用场景自动切换。
Many devices support all three of these profiles. The appropriate profile is selected automatically depending on the application.

The currently-used Bluetooth 5.1 standard only supports connections between 2 devices (source with sink, or gateway with client). The process of connecting two Bluetooth devices is called pairing.
现行的蓝牙 5.1 标准仅支持一对一配对（source 和 sink，gateway 和 client）。连接两个蓝牙设备的过程称为配对。

Only devices that support compatible profiles can be connected to each other, such as A2DP Source with A2DP Sink, or HSP Gateway with HSP Client. To do this, both devices are put into “pairing mode”. A2DP Source or HSP / HFP Gateway devices usually scan for available A2DP Sink or HSP / HFP Client devices and show them in a list on a display. The user then selects the desired device. With car radios (HFP Client) it is also common that the pairing process is additionally secured by comparing and confirming a PIN code displayed on both devices.

Scanning for available devices can be time-consuming, especially when many Bluetooth devices are found in pairing mode. A faster method of pairing is to skip the search process and call the desired device directly with its MAC (Media Access Control) address. This method is mainly used in production testing of Bluetooth devices.
只有支持兼容规范的设备才能互相配对，比如 A2DP Source 和 A2DP Sink，或 HSP Gateway 和 HSP Client。配对时，两个设备都进入“配对模式”。 A2DP Source 或 HSP / HFP Gateway 设备将扫描可用的 A2DP Sink 或 HSP / HFP Client，并将它们列出来。用户选择需要的设备即可。部分设备配对时还需要输入 PIN 码确保安全。

扫描可用设备的过程往往需要花费不少时间，特别是处于配对模式的蓝牙设备很多时。更快的方法是跳过扫描过程，直接通过设备 MAC 地址（硬件地址）连接。这种方式一般在产线上使用。

NTi Audio 的蓝牙测试盒和 FX100 音频分析仪可以轻松快速地测量蓝牙音频设备。测试盒将发射和接收的信号转换为模拟信号，并通过 XLR 接口连接分析仪。它支持以上三种规范。可以手动或全自动配对。配对完成后，FX100 音频分析仪即可自动触发测量。

The NTi Audio Bluetooth Box connected to the FX100 Audio Analyzer allow simple and convenient testing of the Bluetooth interface of audio devices. The received and sent audio signals are converted to analog signals and provided on XLR connectors. All profiles described above are supported. The pairing process can be done manually or automatically. When the pairing process is completed, a trigger signal is sent to the FX100 Audio Analyzer to start the measurement.