Talking about the performance of audio equipment without objective measurements is like describing the taste of food without eating it. Maybe that’s a bit over the top, but the concept is accurate. You’ll hear many folks into high-end audio describe listening experiences that are sweet or emotional. However, those adjectives do very little to describe the physical characteristics of the performance.

Where in the world are we going with this? A combination of several listening tests and lab measurements got us thinking about the Hi-Res Audio product certification. We’ve tested many source units, amplifiers, signal processors, and Bluetooth interfaces that bear this accreditation. What does Hi-Res Audio certification mean? Further, does it mean a product will sound great?

High-Frequency Audio Reproduction

The first part of the certification attempts to correlate extended high-frequency performance with audio resolution. The standard requires amplifiers, signal processors, audio interfaces, source units, speakers, earphones, and microphones to record or reproduce audio frequencies up to 40 kHz.

The inference is that extended frequency response somehow correlates to resolution. In reality, bit depth, in theory, has more to do with resolution than high-frequency performance.

Ask anyone over 30 if they can hear audio frequencies above about 16 kHz, and most will tell you no. Those who think they can ought to have a formal listening test performed. We believe they will be surprised. Most adults we know can’t hear much over 14 kHz.

The argument for capturing audio frequencies above 22.05 kHz (the upper limit of a compact disc) is that harmonics present in the audio change the audible frequency region. While possible, those harmonics will also be present in the recording at audible frequencies. Reproducing them offers no benefit if they can’t be heard. Bats, dogs, cats, rats, mice, owls, and reptiles might appreciate the extra effort and storage bandwidth, but humans won’t.

Benefits of High-Resolution Audio Recording

The most significant benefit of recording higher-frequency content is the overall quality of the recording equipment. A recording studio might have a Universal Audio Apollo audio interface capable of sampling analog audio at 192 kHz with 24 bits of depth. However, those details alone don’t describe the true performance capabilities of the device. The Apollo X8 boasts 130 dB of dynamic range and a THD+N specification of -127 dB. The latter is equivalent to better than 0.0000446% Total Harmonic Distortion and Noise. To put it subtly, that’s ludicrously impressive.

What does this mean for the recording? The recording only captures the audio signal from the microphone at the interface, as the harmonic content added to the signal is imperceptibly low. An order of magnitude worse performance would still be imperceptible. You will get an incredibly clear recording when the engineer mixes dozens of tracks at this quality level.

Actual Bit Depth Comparison

The image below, and dozens like it, are misused in hundreds of applications to infer different quality levels based on bit depth.

The second part of the Hi-Res Audio criteria refers to handling audio files with 24 bits of depth. A common misconception about bit depth is that it also correlates with resolution. In reality, it doesn’t. The benefit of additional bit depth is reducing the noise captured in an audio signal.

Here’s a very real-world example. The image below shows the spectral content of a 1 kHz tone recorded at -80 dB FS, then saved as a 192 kHz, 24-bit file in red. The yellow trace is the same test tone but is saved as a 16-bit file.

When we open the file and check the spectral content, we see that a lot of noise has been added to the 16-bit track. Yes, the information is at a very low level of -98.13 dB for the 16-bit file. Crucially, it’s something that wasn’t in the original recording.

When a music producer creates a modern rock or pop song, they might combine 50 to 80 different tracks or samples. Let’s assume it’s only 60 tracks with 16 bits of depth. After typing a really long equation into Microsoft Excel, we get a noise floor of -90 dB FS. With playback levels of 100 dB SPL, which is easily possible from even modestly robust audio systems, the noise in the recording would be audible during quiet passages.

A 24-bit audio file has a noise floor of around -160 dB FS. I won’t bother doing the math, as no source units or amplifiers perform anywhere near that level. Okay, I lied. That’s about -152 dB of noise with 60 tracks combined. Like I said, it’s not audible.

Sound Quality

Unfortunately, for the Hi-Res Audio designation, the most easily perceptible degradation in audio quality is associated with distortion. Harmonic distortion is far more prominent than noise or high-frequency extension. As we’ve explained repeatedly, distortion is the addition of unwanted harmonic content due to nonlinearities in a speaker, amplifier, signal processor, or source unit.

The Japan Audio Society ignores this significant factor in its Hi-Res Audio certification. Their exact statement regarding audio quality is based on a “hearing evaluation” that is “implemented according to each company’s regulations.” Given that few products publish distortion specifications, it’s concerning that a label intended to designate a product as high quality leaves out this critical consideration.

Hi-Res Audio Wireless

What got us all riled up about the Hi-Res Audio designation? It was a culmination of several listening tests of Hi-Res Audio Wireless products. While the efforts put into optimizing wireless audio transmission over Bluetooth are commendable, the degradation the process causes is significant.

Based on our hands-on experience, playing a Hi-Res Audio Wireless format like LDAC or aptX on a premium-quality source unit degrades the performance to well below what you’d hear with a regular run-of-the-mill solution. Nevertheless, we understand the concept and goal – the execution fails miserably.

If you think for a moment that Bluetooth “sounds awesome,” then it’s time to play some music directly from a USB memory stick. The same goes for wireless connections used in Apple CarPlay and Android Audio. Switch to hi-res tracks you’ve purchased and stored on a USB memory stick. If your system can deliver, the difference will blow your mind! If you don’t hear a difference, it’s time for an upgrade.

Hi-Res Audio Isn’t Necessarily High-Fidelity Audio

We’ve been incredibly fortunate to have the opportunity to measure and audition audio solutions from all the top brands in the car audio industry. Indeed, many solutions sound magnificent. Unfortunately, many make quality and clarity claims that the hardware can’t substantiate. Some of these products bear the Hi-Res Audio logo.

When it’s time to upgrade your car audio system, drop by a few local specialty mobile enhancement retailers and audition the solutions they offer. If you’ve done some research and listened to the same music in the demo vehicles and on the display boards, picking out what sounds terrific is easy.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

A while back, we examined the difference in sound quality between wired and wireless Apple CarPlay. Now that many Android-based smartphones have access to additional audio streaming codecs like LDAC and aptX, it’s time to check out how they perform in terms of signal accuracy and frequency response. We’ll use the Sony XAV-9000ES digital media receiver we tested in May 2024 for the test. Let’s see what happens!

The Test Criteria

The most important consideration in determining sound quality is frequency response. To evaluate this, we’ll conduct two tests. First, we’ll play a five-minute-long white noise track from an Android smartphone while it’s connected to the Sony radio’s USB port. We’ll use the averaging capabilities of our QuantAsylum QA403 to analyze the result. We are looking for as flat a response as possible here.

Next, we’ll connect the phone to the radio wirelessly and repeat the measurement. The frequency response results for an iPhone were similar over either connection.

The second test is to evaluate signal quality. We’ll play a 0dB 1kHz test tone for this test in both wired and wireless configurations. We’ll examine the harmonic content to evaluate how each scenario performs regarding purity. Perfect performance would mean that no additional harmonic information is added to the 1 kHz tone. In the case of the iPhone, the wireless connection couldn’t hold a candle to having the device hardwired to the source unit.

For reference, we’ll include measurements of the white noise and 1kHz test tone tracks played back from a USB memory stick. With an Apple iPhone as the source option, playing your music from a USB memory stick was hands down the best choice.

Frequency Response Testing

We should have mentioned that we are using a Samsung S9 running Android 10 for the testing. Yep, it’s a bit old, but it has LDAC. Should we stumble on a more recent model, we’ll repeat the testing and update.

Let’s dive right into the frequency response results, shall we? First, let’s look at the performance when using a wired connection to the smartphone.

Up first, we have the analysis of the white noise track played back from a USB memory stick. We’ve zoomed in so you can see if there is any roll-off.

Overall, the response looks just as we expected—flat out from 10 Hz to 96 kHz. Now, let’s switch to a wired connection while using Android Auto and see if that affects anything.

It’s clear that the audio signal starts to roll off at about 14 kHz, and it appears to be about 20 dB down by 22 kHz. There’s no audio information above 22 kHz, so the signal is not considered hi-res. Now, let’s switch to a wireless connection and measure the white noise track again.

In this test of the Sony radio and Samsung S9 phone, we can see that nothing above approximately 17 kHz is passed from the radio. We’d really like to try a new phone, though, to confidently assert that the wireless connection is this bad in all cases.

Signal Purity

The next test is to evaluate how the different playback options affect signal purity. In a perfect world, no additional audio content would be added to the test tone. However, every audio device adds some amount of harmonic content. The less added, the more precise and accurate the system will sound, assuming the frequency response remains unaltered.

First, we have the distortion performance when playing our test tone from a USB memory stick.

Overall, the Sony performed well, with a THD+N specification of 0.00581% and an output right around one volt. This would be considered excellent performance. Now, let’s see what happens when we play the same track from the Samsung phone using a wired Android Auto connection.

There’s a little more low-level noise below the 1 kHz tone, but overall, the performance is quite similar. Measured THD+N came in at a still respectable 0.01029%. Finally, let’s try this with a wireless connection.

Just as we saw when using an iPhone, the wireless connection adds a lot of low-level noise. While the graph looks much worse, the 3 kHz, -91 dBV spike remains the primary factor in determining total harmonic distortion. As such, the measured performance only decreases slightly to 0.01139%. This is still considered to be a good distortion number.

Conclusions on Wired Versus Wireless Android Auto Sound Quality

From the standpoint of our 1 kHz signal purity test, it remains clear that a USB connection outperforms wired or wireless connections. This is especially true regarding frequency response. The Android Auto connections would sound duller and less detailed than playing music from a USB memory stick.

If you’re after the best sound quality possible from a premium multimedia receiver, then put your music collection on a USB memory stick and connect that to your radio. If your radio doesn’t support the latest high-resolution audio formats, drop by a local specialty mobile enhancement retailer to see what they have to offer to upgrade the clarity of your mobile audio system.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.