> For the complete documentation index, see [llms.txt](https://qudelix.gitbook.io/home/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://qudelix.gitbook.io/home/general/bluetooth-codec-control.md). # Bluetooth Codec Control ## Codec / LDAC FS Qudelix-5K and Qudelix-5K Plus operate as Bluetooth audio receivers, or **A2DP Sink devices**. When a smartphone, tablet, PC, or other Bluetooth source connects to Qudelix, the source device selects the Bluetooth audio codec and, in the case of LDAC, the operating sample rate from the capabilities reported by Qudelix. In many source devices, however, codec and sample-rate selection is not easy to control. Some devices do not provide a user-accessible codec selection menu. Others may allow manual selection, but the setting can be reset whenever Bluetooth reconnects, requiring the user to configure the codec or sample rate again. Qudelix provides **SUPPORTED CODEC** and **LDAC FS** options as a workaround for these cases. By limiting the codecs and LDAC sample rates that Qudelix advertises as supported, you can restrict the choices available to the source device. The source device then selects from the remaining available options. {% hint style="info" %} Qudelix does not directly command the source to use a specific codec or sample rate. It restricts the capabilities presented by the Bluetooth Sink so that the source device is effectively guided toward the desired configuration. {% endhint %} ### Supported Codec The **SUPPORTED CODEC** menu controls which Bluetooth audio codecs Qudelix reports to the source device as supported. Depending on the product and firmware, available codecs may include: * SBC * AAC * aptX * aptX HD * aptX Adaptive * Sony LDAC™ The codec actually used for the Bluetooth connection is selected by the **source device**. For example, simply enabling LDAC on Qudelix does not force the source device to use LDAC. The source must also support LDAC and select it during the Bluetooth connection. However, by disabling unwanted codecs on Qudelix, you can reduce the choices available to the source. For example, suppose a source device supports: * SBC * AAC * aptX * LDAC and Qudelix also advertises all four codecs. The source device is free to select any codec according to its own Bluetooth implementation. If you want the connection to use LDAC whenever possible, you can disable AAC and aptX on Qudelix and leave only the required fallback codec and LDAC available. The source will then see a much more limited codec list and select from those remaining options. This is especially useful on source devices where the preferred codec cannot be permanently stored. {% hint style="info" %} SBC is the mandatory codec defined by the Bluetooth A2DP specification. It provides the basic compatibility fallback for Bluetooth stereo audio. For this reason, SBC is normally kept enabled even when other codecs are preferred. {% endhint %} Normally, the default configuration with all supported codecs enabled provides the widest compatibility. The codec restriction option becomes useful when: * the source device does not provide a codec selection menu, * the desired codec must otherwise be manually selected after every connection, * the source repeatedly selects an unwanted codec, * you want a particular source device to consistently select from a smaller codec set. The setting is stored on the Qudelix side, so the codec capability restriction remains associated with the Qudelix device rather than depending on a source-side developer option or temporary OS setting. ### LDAC Sample Rate Sony LDAC supports multiple sample rates: * 44.1 kHz * 48 kHz * 88.2 kHz * 96 kHz The **LDAC FS** menu controls which of these sample rates Qudelix reports as supported when an LDAC connection is established. As with codec selection, the actual LDAC sample rate is selected by the **source device**. By disabling unwanted sample rates, however, you can restrict the choices available to the source. Many Android devices automatically select the highest LDAC sample rate reported by the Bluetooth receiver. If 96 kHz is available, Android may therefore establish the LDAC connection at 96 kHz even when the original audio source is 44.1 kHz. For example: **44.1 kHz music → Android audio system → 96 kHz LDAC** In this case, the source audio is resampled to 96 kHz before being sent to the LDAC encoder. If you prefer to avoid this behavior, you can disable 88.2 kHz and 96 kHz in the Qudelix **LDAC FS** menu. The source device will then have to select from: * 44.1 kHz * 48 kHz This provides a practical way to control LDAC sample-rate behavior even when the source device does not provide a persistent sample-rate setting. #### 44.1 kHz Only If most of your music is 44.1 kHz and you want the Bluetooth connection to remain at 44.1 kHz, you can enable only: * 44.1 kHz and disable: * 48 kHz * 88.2 kHz * 96 kHz Qudelix will then advertise only 44.1 kHz as an available LDAC sample rate. If the source device accepts that configuration, it will establish the LDAC stream at 44.1 kHz. This eliminates the need to manually select 44.1 kHz again whenever the Bluetooth connection is re-established. #### LDAC Sample Rate and Bitrate The LDAC sample rate and LDAC transmission bitrate are separate parameters. For example: * 44.1 kHz / 990 kbps * 96 kHz / 990 kbps use different audio sample rates while operating at approximately the same LDAC transmission bitrate. A higher sample rate therefore does not automatically mean that more Bluetooth bandwidth is available. If the original audio is 44.1 kHz, converting it to 96 kHz does not add new audio information. It only changes the sample rate presented to the LDAC encoder. For this reason, selecting the highest available LDAC sample rate is not necessarily required for every source. ### Source Device Still Makes the Final Selection Qudelix operates as the Bluetooth Sink and advertises a list of supported capabilities. The source device still performs the final codec and sample-rate selection. The Qudelix options work by **limiting the available choices**. For example: **All codecs enabled** `SBC / AAC / aptX / aptX HD / aptX Adaptive / LDAC` The source decides which one to use. If the Qudelix codec list is restricted to: `SBC / LDAC` the source can now select only from those advertised codecs. The same principle applies to LDAC sample rates. ### Re-Pairing Some smartphones and operating systems cache Bluetooth capability information obtained during pairing. After changing **SUPPORTED CODEC** or **LDAC FS**, simply disconnecting and reconnecting may not always cause the source device to read the updated capability list. If the new setting does not take effect: 1. Apply the new settings on Qudelix. 2. Disconnect the Bluetooth connection. 3. Remove or forget Qudelix from the source device's Bluetooth pairing list. 4. Pair Qudelix again. The source device can then obtain the updated codec and sample-rate capabilities. {% hint style="info" %} For normal use, leaving all supported codecs and LDAC sample rates enabled provides the greatest compatibility. The codec and LDAC FS restrictions are primarily useful when the source device does not provide convenient or persistent control over Bluetooth codec settings. {% endhint %} **SUPPORTED CODEC** controls which codecs Qudelix advertises to the Bluetooth source. **LDAC FS** controls which LDAC sample rates Qudelix advertises to the Bluetooth source. By limiting these advertised capabilities, Qudelix can provide a practical workaround for source devices that otherwise make codec or sample-rate selection difficult to control.