Saturday 26 August 2023

Part II: Comparison of Bluetooth Fidelity - AAC encoder quality (Android 10 & 13, Windows 11, Apple iPhones & Mac)

Greeting everyone, time to jump into Part II of our assessment of lossy Bluetooth music transmission.

In Part I, we examined the use of an Android 10 device (Huawei P30 Pro) as audio transmitter showing the differences between the codecs as played back with the AIYIMA A08 PRO amplifier and its Qualcomm QCC5125 Bluetooth SoC. Please refer to that article for details about the methodology and comparison with the output from a high resolution Topping desktop DAC.

For this Part II, let's focus on the Advanced Audio Coding (AAC) codec which has become a very popular option. Other than the universal default SBC, AAC is probably the most common one for music transmission on account of the fact that the "elephant in the room" - Apple - uses this across its product lines as their standard codec running at 256kbps. Given the amount of use, this is basically a practical standard for quality music transmission over Bluetooth.

Given the broad range of computers/tablets/phones used among family members here, when I'm looking for wireless headphones, I would want to make sure the device supports AAC; probably more so than aptX or LDAC.

Note that there is actually a "family" of AAC profiles from the early Low Complexity AAC (LC-AAC) originating in 1997 up to later versions like Extended High Efficiency AAC (xHE-AAC) released in 2012. As end users, we're generally not privy to such details so I'll just use the generic term "AAC" in this article.

Saturday 19 August 2023

Part I: Comparison of Bluetooth Fidelity - SBC, aptX, AAC, LDAC (Android 10 source)

Blue ring around power/volume knob = Bluetooth input.

I've been wanting to do this for awhile. The last time I had a look at Bluetooth playback quality was way back in the days of the Oppo Sonica DAC in 2017.

Bluetooth has been our ubiquitous wireless audio transmission technology for more than 2 decades now; Bluetooth 1.0 was released in 1999 but it took a few years for the number of supported devices to grow and costs to come down. Since then, with subsequent versions, we have seen an increase in bandwidth, codecs, transmission range, and power efficiency.

Currently, we are at Bluetooth 5.X (version 5.0 standard released 2016) with the potential for up to 2Mbps transfer rate and distance maximally up to 240m (800ft)! These are clearly ideal numbers. Bluetooth transmits in the 2.4GHz bandwidth like WiFi but can "hop" (Frequency Hopping Spread Spectrum) between 79 channels, 1MHz wide, so there are usually no issues with coexistence. 

Given the 2Mbps limitation, lossless audio transmission would be a problem. Lossless 16/44.1 stereo is already just over 1.4Mbps uncompressed. Yes, we could losslessly compress but compression ratios are variable. Due to inevitable errors in transmission plus protocol overhead, in practice, at most we should think of Bluetooth 5 as operating around 1Mbps reliably under reasonable, if not close to ideal, conditions with transmitter/receiver nearby.

Saturday 12 August 2023

The Different Types of Subjectivisms in Audiophilia (And How to Get Rid of Them) - guest Taylor Christensen

By Taylor Christensen

I joined the audiophile hobby less than 10 years ago, and, as a person who relies heavily on understanding and applying scientific literature in my day job, I was baffled (pun intended) to discover the extent to which the culture of this hobby is shaped by “pseudosciency” beliefs and even frank scientific ignorance, especially when considering the high prevalence of the audiophile community being well educated and affluent.

Since then, I have thought a lot about this phenomenon. Whenever I am trying to make sense of the world, I find that exhaustive, mutually exclusive categorizations help a great deal, and I have come up with such a categorization that helps me organize and understand the strange things we see in this culture.

To communicate clearly, I need to explicitly define any words whose definitions may be ambiguous – in this case especially, because they sound very similar. Therefore, let me start with three definitions.

The first one, which I will be using frequently throughout this article, is "subjectivism," which I am defining as "any false belief in audibility".

Contrast that with the second word I want to define: "subjectivity," which relates to a person having a personal preference.

Tuesday 1 August 2023

REVIEW / MEASUREMENTS: AIYIMA A08 PRO - TI TPA3255 Class D amp with AAC/LDAC/AptX Bluetooth input. On "giant killers" and "CHEAP" amps. Goodbye TIDAL MQA.

Over the last while it has been interesting checking out some TI TPA3255 "PurePath" chip Class D audio amplifiers such as the Fosi Audio TB10D [Upgraded] and AOSHIDA A7.

As you can see in the image above, I've got another one to put on the test bench for a look and listen - the AIYIMA A08 PRO (currently <US$130). Depending who you read/listen/watch, you'll see supporters who like the amp, sometimes calling it a "giant killer" of sorts, such as this blog post, or there are detractors like Andrew Robinson who seem to think these kinds of amps are only good in the nearfield and below 60dB SPL (see from 10:30). We'll talk about this below. :-)

As usual, let's start with a peek at what you get for a low price...