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.
Here I will explain the different aspects of bluetooth for audio and how it affects sound quality. A good signal would be one that is most accurately reproduced. The source signal can only be delivered into mechanical energy(the sound) with little degradation to a lot of degradation when strictly discussing THD(total harmonic distortion). In this case, I am defining “degradation” as distortion since it alters the source signal. There are many contributors to THD throughout the audio path, bluetooth “can be” one aspect of altering the signal.
Source signal: There are many source signals for audio today. Some examples would include analog such as vinyl records tape, or digital, such as cd player. If you are looking for the highest possible source signal you would want to go with analog. Today almost everything is digital due to the convenience factor, vinyl records and turntables are dying because they are no longer being supported by current generation music. These systems are also highly prone to scratches, dust, and are just not very portable. They have been mostly done away with due to the ever growing popularity of portable and convenient audio. For example, televisions, computers, cellphones, tablets, mp3 players, and cd players, all operate in the digital format of audio. If you look at the biggest database of audio today, it is the internet, and any devices which connect to the internet are digital devices. Although technically possible to take a digital signal and convert it to analog, it would be useless, because remember, the signal can only be as good as the source, (in this case digital) not better.
Bluetooth is one instance of digital audio and is popular due to its even further convenience factor by eliminating the need for wires to deliver the audio signal to an amp. Lets break down the different types of digital audio sources by the bit rate that they can provide, for some clarification and comparison. 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. Lossless will use as many bits as required, no more and no less.
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.
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.
What about Bit-Depth?
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 codec