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Audio over bluetooth is often shunned by audio enthusiasts, but is it really justified? Today we will discuss why not all audio over bluetooth is equal. 

The fact is that audio over bluetooth does have far more potential than has been demonstrated by the vast majority of BT products made available to date. The problem of BT rarely showing its full potential is of course due to many factors, with none being greater than the poor electronics design of nearly every popular unit on the market. While maximizing profits through low-cost (too low) components and planned obsolescence may be great for corporate conglomerates, such strategies certainly do no service to consumers and especially those who have a preference for actual quality in the products they buy. 

A good signal would be one that is most accurately reproduced. The reason a source signal is so important is because it is the defining factor of how good a system can be capable of being. For example, if your source signal is missing information or if it is already suffering degradation, you can’t get any of that back later on in the signal path. Bluetooth can be one contributor to the altering of source signal by means of bitrate compression.

Lets break down the different types of digital audio sources by the bit rate that they can provide, for some clarification and comparison. Please note: Lossless will use as many bits as required to deliver the entire information to the source, no more and no less. Lossy on the other hand will compress the bitrate the information to the source in a smaller packet size.

  • Digital Cd Player: 1,411kbps-CD is Lossless unless converted to a lossy format, for example converted to Flac remains lossless, but converted to mp3 becomes lossy.
  • Mp3: 128kbps-256kbps Lossy
  • Flac- bit rate can vary based on music, but is lossless.
  • Wav-bit rate can vary bsaed on music, but is lossless.
  • Bluetooth bitrate by audio codec supported: 
  • Qualcomm APTX: 352 kbps Lossy
  • APTX HD: Lossless up to 576 kbps, can be a combination of lossless and lossy if bitrate of the track exceeds 576kbps in lossless format.
  • LDAC: varies up to 990kbps-uses combination of Lossless and Lossy techniques. This depends on distance and signal strength and you generally need to be very close to the device otherwise the bitrate will be low.
  • AAC: A2DP: up to 328 kbps
  • SBC 345kbps max but typically less. fallback standard

But what does this mean?

Bit rate is exactly what it sounds like, how many bits of data can be processed over time. A compressed signal can be broken down into 2 types, a lossy compression, and a lossless compression. A lossy compression means that once the signal is compressed, it can’t be uncompressed and retain all of the original signal integrity, and a lossless can be uncompressed and be an exact replica of the original signal. For example A lossy compression will bring lower quality audio because it alters the sound data by discarding some bits of information by using an algorithm that looks at frequencies least likely to be audible and then clearing out those bits of information, thereby reducing the size. 

So is bluetooth all that bad?

This depends on the type and format of music you are listening to. For example, music on most streaming services such as youtube, pandora, spotify, etc.. most commonly use mp3 lossy bitrates anyway. So say you buy the best HI-FI system on the planet and then listen to music from these sources. Would Bluetooth in itself further degrade it? Probably not because most bluetooth audio codecs support high enough bitrates that wouldnt result in any further degradation to the bitrate. What about if you have a bunch of MP3’s on your phone would they be further degraded by good quality audio codecs? Probably not. Now say you wanted to listen to some high quality digital audio formats such as FLAC or WAV. Would bluetooth degrade these? Well that depends. For example APTX-HD can support up to a 576kbps bitrate and remain lossless. So if the bitrate of your high quality FLAC or WAv file did not exceed 576kbps then no information would be lost. If it did exceed it, then you would start to get some compression, whether or not the amount of compression would be enough for you to notice or not is debatable.

So if in a lot of cases bluetooth can be “HI-FI” why do most bluetooth speakers sound bad?

There are many factors other than just bluetooth codecs here. First off, bluetooth modules also contain an onboard pre-amp. Within most modules it is a very poor quality one, so you are already starting off with a poor quality source signal right off the bat. There are some very high quality pre amps in premium bluetooth modules such as the CSR8675 but they are used by almost no bluetooth speakers. Most of the bluetooth speakers made also use very poorly and cheaply designed amplifiers, speakers, and enclosures, which all contribute to the poor sound quality. When choosing a device its always important to look at what the designers were trying to achieve with it.

What about Bit-Depth in Bluetooth?

Aside from “bit rate” which affects frequencies, there is also “bit depth” which affects dynamic range which is the db or spl difference between the softest and loudest parts of the song. You may be familiar with dynamic range by a post processing DSP called “loudness equalization” found in a lot of audio control software today, which takes music and either minimizes or maximizes the sound db difference from the quietest points to the loudest points of a song. This “can “completely ruin the “integrity” of the source signal because it is altering the natural dynamic range in the source of the song. A higher bit depth can also be thought of in terms of a resolution because it can set the maximum loudness of a recording. For example as the bit depth increases, so does the dynamic range. So where a 16 bit depth is 96db of dynamic range, a 24 bit depth is 144db of dynamic range. A higher bit depth up to 24 bits is generally best if it is how it was recorded originally but it may not become apparent unless in a studio.  Bluetooth codecs also come in here too. for example: APTX-HD supports 24 bit depth with 192khz sampling and is generally thought of as the top end of bluetooth audio. APTX supports 16 bit depth A2DP, AAC, SBC etc…. support 16 bit depth.

An important note: In order to take advantage of a specific bluetooth codec such as aptx-hd, the codec needs to be supported on both the receiving and transmitting end. If a codec is not supported by one of the devices, then it will “fall back” to the best codec which is supported by both devices.
 *The ONLY™ supports APTX-HD and uses the premium CSR8675 module discussed as the best throughout this article.

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