Bluetooth Applicability in High-Fidelity Audio Systems

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Engineering Student Trade Journal Articles College of Engineering

Fall 2020

Bluetooth Applicability in High-Fidelity Audio Systems Bluetooth Applicability in High-Fidelity Audio Systems

Garrett Scheiber

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GARRETT SCHEIBER| College of Engineering Valparaiso University

Bluetooth Applicability

in High-Fidelity Audio

Systems

Do the abilities of Bluetooth technology allow for its use as a transmission medium

for high quality audio?

Music enthusiasts have sought the highest quality audio playback since audio recording

technology was developed. Amplification techniques and speaker constructions have been

improved to give clearer sound. Despite these advances, transmission has continued primarily

through wire. Developments in wireless technology have the possibility to change transmission

of audio between speakers, amplifiers, and other audio devices. Bluetooth has the potential to

solve this transmission problem, but the abilities must be investigated before any conclusions are

made. Bit rates and other characteristics of common Bluetooth versions must be analyzed and

compared to the bit rate of high-fidelity music to assess Bluetooth’s suitability.

Bit rate is a common measurement of

music quality. It consists of a sampling rate, a

level measurement, and a classification of loss.

This is illustrated in Figure 1. The black

waveform is the original recording waveform of

the music. The time between each vertical line is

the sampling rate (a higher sampling rate

translates to a lower delay between samples,

which increases the accuracy). The level

measurement is the position of the wave at a

certain point (the height of each horizontal line).

A higher number of bits devoted to level will

result in an increased level accuracy. Loss

classification is either lossless (no audio data

loss during compression) or lossy (audio data is

lost during compression). For example, CDs

have a sampling rate of 44.1 kHz with 16 bits

devoted to the output level which gives a bit rate of 1,411.2 kbps (which is considered lossless)

for two channel audio. For this investigation, CD quality (1,411.2kbps) will be considered the

lowest possible quality for high-fidelity music.

Wired transmission’s bit rate is limited solely by the sending node, the receiving node,

and the source quality of music (e.g. streaming services, records, or CDs). This gives different

Figure 1:

The difference between different bitrates and

the effect on sound accuracy.

GARRETT SCHEIBER| College of Engineering Valparaiso University

audio qualities the opportunity to be transmitted at their native bit rate (the source quality).

Alternatively, wireless transmission uses radio waves to transmit data between nodes, which is

limited by the transmission rate of the nodes

Bluetooth 5.0 (the latest version of Bluetooth) has a transmission rate of approximately

1,400kbps, which seems to meet the requirements for transmitting CD quality audio (the

established baseline for high-quality audio). Solely analyzing the transmission rate gives a

misleading outcome. The “other characteristics” mentioned above must also be considered.

Bluetooth version differences and congestion can have a negative impact on the transmission

rate. Although compatible, using different versions of Bluetooth at the sending and receiving

nodes will restrict the transmission rate to the lower rate of the two nodes. Congestion in the

radio frequency wavelength (other active Bluetooth transmissions) will also limit the

transmission rates. The only potential positive factor to consider is the codec used in

transmission.

Codecs compress data

before transmission (some

audio codecs are shown in

Figure 2). Most common

codecs are lossy, being

optimized for lower

quality audio streaming

services (Spotify, Apple

Music, Pandora, etc.). As

shown, only one codec

exists which is both

compressed and lossless

(FLAC). Practically,

FLAC is not a standard

codec in most devices, and

therefore would not be

beneficial to common users. Considering the factors of version difference, congestion, and codec

applicability previously described, Bluetooth is not currently applicable to high-fidelity music

transmission.

Although current versions of Bluetooth are not applicable to high-quality audio

transmission, changes in future versions can be made to rectify this. Advances in transmission

speeds will likely be offset by increased use of Bluetooth in a wider variety of applications,

making transmission rate improvements negligible. Despite this, codec modification and priority

frequencies could deem Bluetooth applicable in high-fidelity audio transmission. Widely using

lossless compression codecs similar to FLAC would decrease the bit rate necessary to transmit

high-quality audio, while preserving the original signal. The transmitter would analyze the audio

source, classifying it as high or low- quality and communicating this to the receiving node. Both

nodes would then transition to the high-quality codec and begin the transmission.

“Priority” frequencies could be implemented, which would reserve a certain fraction (of

the 79 different frequencies illustrated in Figure 3) for designated uses (these could be audio or

professional related). The use of priority frequencies would reduce the congestion in these

Figure 2: Different Bluetooth codecs with advantages and disadvantages.

GARRETT SCHEIBER| College of Engineering Valparaiso University

frequencies, allowing

for higher

transmission rates

where desired. Both

of these changes (to

codec use and priority

frequency allocation)

could improve

Bluetooth’s viability

in high-fidelity audio

transmission.

Bluetooth versions do not currently exibit the abilities for high-fidelity music

transmission. Transmission speeds are adequate, but limitations related to codecs, congestion,

and differing Bluetooth versions prevent Bluetooth from being a realistic alternative to wired

audio transmission. As shown, modifications to codec availability and frequency allocation could

theoretically make Bluetooth a viable method of audio transmission.

Figure 1: https://www.izotope.com/en/learn/digital-audio-basics-sample-rate-and-bit-depth.html

Figure 2: https://www.soundguys.com/understanding-bluetooth-codecs-15352/

Figure 3: https://sites.google.com/site/nearcommunications/adaptative-frequency-hopping

Figure 3: A graphical representation of the frequencies used in Bluetooth transmission.