by DoBlue
Newly Released Do Blue SLASH4 - Hi-Fi Bluetooth DAC Receiver for Car Audio
Newly Released Do Blue SLASH4 - Hi-Fi Bluetooth DAC Receiver for Car Audio
Introduction
Do Blue, known for selling high-quality Bluetooth DAC receivers ‘SLASH series’ with a compact and innovative design, has now introduced a new model called SLASH4. This model is specifically designed for users who want to enjoy music with better sound quality through high-quality wireless audio codecs in their cars. Focusing on essential features, DO Blue has condensed the size and components to a minimum in the SLASH4, providing a compact and efficient solution for an enhanced in-car audio experience.
I have been using and enjoying both the first and second generations of the Do Blue SLASH6, so I am curious and excited about how well they have improved the new Do Blue SLASH4.
I also equipped my car with a full-option car audio system when purchasing it. However, I was disappointed because it only supports the basic codec for Bluetooth, and the playback through USB memory does not properly support high-quality audio files.
The Do Blue SLASH series offers a variety of features depending on the model, ranging from products with only a built-in Bluetooth receiver function to those with USB DAC, optical input and output, and even an integrated headphone amplifier. One consistent feature across all models is the unique design where you can simply plug it into the RCA jacks. Additionally, they all support high-quality Bluetooth audio codecs and are equipped with high-quality DACs.
However, the existing Do Blue SLASH series can be connected not only to home hi-fi amplifiers but also to car audio systems.
You can connect the Do Blue SLASH series to a car audio system in various ways, such as (1) removing the car audio amp module and connecting it to the internal terminals, allowing it to be concealed within the car, or (2) connecting RCA cables to the internal terminals of the car audio amp module and then connecting the external RCA cables to the SLASH Bluetooth receiver. Additionally, (3) you can connect the output terminals of the SLASH Bluetooth receiver to the AUX input of the car audio, or (4) in the case of car audio systems with optical input, connect the optical output of a SLASH model equipped with optical output.
When connecting existing SLASH products to a car audio system, there are some inconveniences, such as the need to remove the car audio amp module and perform modifications or, if not integrated into the main unit, the need to find a suitable place to mount it. Additionally, in the case of lower-end models, there may be difficulty in filtering out noise from the car's power supply, requiring the addition of a separate noise filter.
The newly released Do Blue SLASH4 actively incorporates consumer feedback regarding these inconveniences and is designed as a compact Bluetooth receiver DAC for vehicles, packed with essential features in a size comparable to a USB memory stick.
So, I tried using it in my car which is over 10 years old.
Exterior and Main Features
The recently updated SLASH box has an appearance reminiscent of gift packaging. The SLASH logo on the side of the box is printed in a handwritten style.
On the back of the box, detailed specifications of the SLASH4 are listed.
If you are using this product for the first time, it is advisable to read the user's manual before trying it.
The newly released Do Blue SLASH4 model resembles a USB memory stick.
The SLASH4 main body is securely protected by a hard foam package.
As an additional accessory, a 3.5mm AUX stereo audio cable is included.
The terminals are gold-plated, and the plug molding of the cable features the printed SLASH logo.
The Do Blue SLASH4 Bluetooth DAC receiver has a design resembling a USB memory stick, unlike the traditional SLASH series. On the top surface, there is the SLASH logo and an LED indicating the operational status.
Despite its small size, the Bluetooth chip and DAC chip used are identical to those of higher models, and it includes a built-in power purification circuit to filter out noise from the car's power terminal.
On the bottom of the Do Blue SLASH4, the product type and KC, FCC certification marks are printed.
- Judging by the FCC mark, it seems that it is also exported to the United States.
- SLASH Quad DAC Wireless Receiver
- Made in Korea (Yes, Do Blue is a Korean company, and it was manufactured in South Korea.)
The Do Blue SLASH4 Bluetooth DAC receiver can be used by plugging it directly into a USB-A type power source.
On the side, there is an elongated button.
This button is used for entering pairing mode or initiating a reset.
There is only one audio output, a 3.5mm jack.
The 3.5mm jack serves as an analog stereo output and is also used as an optical output.
Not only does it look like a USB memory stick, but it is also about the same size.
When placed side by side with the SanDisk USB memory stick that I am using, it is almost the same size.
▶ This image shows the key features of the Do Blue SLASH4 Bluetooth DAC receiver.
•Supports high-quality Bluetooth codecs such as LDAC, aptX Adaptive, and aptX HD
•Supports low-latency aptX LL codec for minimal audio delay
•Powered by Qualcomm QCC 5125 Bluetooth chipset
•ESS ES9219 Quad DAC for superior audio performance
•Automatically connects upon engine start (Immediately connects to the previously paired device when powered on)
•Isolated DC-DC converter for power noise prevention
•Equipped with ultra-low noise LDO (DC Voltage Drop Regulator) for enhanced performance in reducing noise.
▶ SLASH4 Key Features (image source: captured from product introduction page)
The following is a summary of the features.
* Chipsets and Bluetooth codecs used are the same as SLASH6
* No complex installation process required, really easy to use it
User Experience
▶ Here's how to enter pairing mode:
(1) When you initially connect SLASH4 to power, it automatically enters Bluetooth pairing mode.
(2) If you want to pair it with another device while it's already paired with a device, press the button on the side once to enter pairing mode again.
(3) If you want to erase all pairing records and reset the device, press and hold the button on the side for more than 1 second. After the reset, it will enter pairing mode again.
(4) After the reset, it will enter pairing mode again.
▶ The Bluetooth device is recognized as ‘SLASH4’
When searching for devices on smartphones or DAPs, it appears as ‘SLASH4’.
When connected to a device that supports the aptX Adaptive codec, a message indicating 'aptX Adaptive audio' connection is displayed. Below is a captured image of the screen connected to an LG Velvet smartphone.
▶ Supports various high-quality Bluetooth audio codecs
When checking the codecs in the developer options, it is confirmed that LDAC, aptX HD, aptX, AAC, and SBC codecs are also supported.
When connected via Bluetooth, the LED color varies depending on the codec in use.
▶ Refer to the image below for the LED color corresponding to the connected Bluetooth audio codec.
When connected via high-quality Bluetooth audio codecs, the LED color appears as follows: white for LDAC codec, sky blue for aptX Adaptive codec, and green for aptX HD codec.
It reliably connects well with Digital Audio Players (DAPs) that support high-quality Bluetooth codecs.
▶ The output signal exhibits almost a flat frequency response
I played a ‘pink noise’ sound with a flat characteristic across different frequency ranges from the source device connected by aptX Adaptive codec. Simultaneously, I recorded the output signal by connecting the provided AUX cable to the 3.5mm audio output jack of SLASH4.
Then, I loaded the original 'pink noise' wave file and the recorded signal into the Audacity audio tool to check the spectrum.
The results, as shown in the image below, indicate that the audio output of SLASH4 exhibits characteristics almost identical to the original audio signal. However, there is a noticeable drop in reproduction characteristics especially in the super high-frequency range (above 16kHz). There is also a very subtle attenuation in the extremely low-frequency range (below 20Hz), which is presumed to be primarily caused by the device matching characteristics with the connected cable and is negligible in terms of its effect on sound.
Even when playing a sweep audio signal and examining the waveform, it is observed that there is a noticeable drop in reproduction capability in the super high-frequency range.
However, these characteristics do not seem to be due to the characteristics of the DAC chipset and amp circuit.
While mentioned in my SLASH6 user experience, I'll reiterate this point as it is crucial for better understanding.
* Here, I want to clarify a couple of points:
1) The lack of reproducibility of the ultra-high frequency range is not the limit of SLASH6, but the limit of the Bluetooth codec.
2) This characteristic does not cause any noticeable problems in listening, and it is a very reasonable choice in an engineering manner.
The reason for transmitting the signal in this manner is that if you have to sacrifice some data within the limited wireless transmission bandwidth, we can find it more rational to sacrifice the ultra-high frequency range that is difficult to perceive with the human ear.
Between 16kHz and 20kHz, there's about 4kHz band of audio signal, but it carries an entirely different level of information compared to the 4kHz in the lower frequency range in terms of perceptual audio.
For example, 16 kHz and 20 kHz are less than half an octave difference, but 20 Hz to 4 kHz has a range of sound that exceeds 7 octaves (just under 8 octaves). In addition, it belongs to the audible band that people can hear very well.
So, which range of 4 kHz band would you choose to stream more fully packed?
No matter who makes the decision, after pondering upon the above facts (even if you actually check them with your ears), it would be a much wiser decision to abandon a band above 16 kHz and transmit lower band signals more faithfully (fully packed).
And I'm a middle-aged person who can't defy biological aging, so I can't hear the frequency range above 16 kHz anyway.
Therefore, from my perspective, there is no issue with the loss in frequencies above 16 kHz, and, if anything, it would be preferable for the lower frequency range to be reproduced more faithfully.
Delivering excellent sound quality with the benefits of high-quality wireless audio codecs
Due to the high-quality wireless audio codecs with 24-bit high resolution, when I listen to the music played with my ears, the difference compared to the original file is minimal.
It provides quite dynamic and high-resolution sound that is challenging to distinguish from the original.
Of course, even with high-quality codecs, due to the characteristics of using lossy compression Bluetooth audio codecs with a bandwidth limited to within 1Mbps, as discussed earlier, there is a drop in reproduction capability in the super high-frequency range. Therefore, individuals with excellent hearing, capable of discerning sounds above 16kHz, may notice this difference.
Furthermore, since the predominant frequency ranges of vocals and various instruments mostly exist within the range below 10kHz, in typical music listening scenes, it can be considered challenging to perceive the difference clearly with the ears.
▶ Sample sound directly recorded from the playback output of Do Blue SLASH4
The video below is edited with audio files recorded from the output of the Do Blue SLASH4 Bluetooth receiver, connected via high-quality wireless audio codecs. Various pieces of music are played briefly during the video.
Honestly speaking, it provides such good sound quality that if you match the signal levels between the original and the recorded output, the difference is almost imperceptible.
In the video below, there is actually some degradation in audio quality during the process of conversion to video and uploading to the blog system. Therefore, please note that the sound you hear in the video may be slightly less accurate compared to playing the recorded sound file directly. Please keep this in mind while watching the video.
So, I can say that how it sounds in your car audio will now depend on the level of your car audio amp and speaker system.
▶ Optical output allowing the high-quality signal to be transmitted directly to advanced car audio systems
Do Blue SLASH4 also outputs optical signals simultaneously through the 3.5mm jack.
So, it's also a significant advantage that you can connect it to some high-end car audio systems with optical input using an optical cable. This allows the direct transmission of high-quality audio signals, encoded and decoded using high-quality Bluetooth audio codecs.
■ Trying SLASH4 with my car audio
My car is over 10 years old, but it was fully equipped with audio options including a subwoofer when I purchased it.
However, since it's an older car model, it doesn't have a USB-C port or Android Auto functionality.
It can play music files from a USB drive or receive analog sound from external devices through the AUX input. While it does offer Bluetooth connectivity, it does not support high-quality audio codecs.
It has connectivity to iPods and iPhones by USB, but connecting the iPhone with a USB cable feels a bit cumbersome, so I have used it rarely.
Anyway, when using Bluetooth connection, the lack of high-quality audio codecs diminishes the satisfaction.
▶ Simple connection and ease of use
Plug the SLASH4 into the USB port, and as soon as the car is powered on, the SLASH4 operates immediately.
Connect the provided cable to the 3.5mm audio output jack of the SLASH4 and plug the opposite end of the cable into the AUX input jack of the car audio system to complete the installation.
If your car does not have a USB-A port, you can use an accessory designed for USB power extension, allowing you to charge various USB devices or provide power.
My car's audio system recognizes when a cable is plugged into the AUX jack and automatically switches 'input mode' to the external device. If it doesn't automatically recognize and switch to AUX input, you may need to manually set the input to "AUX" in the input selection menu.
If you want to switch back to the AUX mode after using other media input modes like FM radio or CD player, you'll need to adjust the settings through the input selection menu.
Once you pair your smartphone or DAP (Digital Audio Player) with Do Blue SLASH4, the device will automatically connect to the last paired device every time the car power is turned on and Do Blue SLASH4 powers on.
Therefore, with the car audio input mode set to AUX input, as soon as the car is started and Do Blue SLASH4 powers on, you can immediately play music or media through the smartphone or DAP that is connected to SLASH4.
▶ The audio latency is minimal., ensuring good lip sync during video playback as well.
The use of a chipset supporting aptX Adaptive and aptX LL codecs ensures minimal audio latency.
When watching videos on YouTube, the synchronization is well-maintained, and there is no noticeable audio delay, providing a satisfying video experience.
■ To use wired earphones or headphones with SLASH4
The output terminal is a 3.5mm earphone terminal, so can't we just plug earphones or headphones directly into SLASH4?
The fundamental idea behind the new SLASH4 is that it's designed as a Bluetooth receiver for vehicles. But, you can also use it with wired headphones or earphones that don't support wireless connections.
Of course, the device itself is quite small, but it's not the type with a built-in battery. If you want to use it on the go, you'll need to connect it to an external power source like a power bank(portable USB battery). However, considering it adds high-quality Bluetooth functionality to your favorite wired headphones, it seems like a pretty good combination.
(It would be perfect to have a small finger-sized external battery and a 'ㄷ'-shaped USB-A jack extension.)
However, since SLASH4's output is not very powerful, using earphones should be fine, but for headphones, you may need to connect models with higher sensitivity to achieve better sound quality.
When connected to a DAP with LDAC, and enjoying high-quality lossless music, the fidelity of the sound is noticeably excellent.
Because the tonal balance is very flat and there is no additional filtering or coloring, depending on the earphones (headphones) you use, it might sound somewhat dry.
A concluding remark
: SLASH4 provides excellent sound quality with high-quality Bluetooth audio codecs, and it's small and convenient.
The newly released Do Blue SLASH4 is a high-quality Bluetooth DAC receiver that features a body the size of a USB memory stick. It supports high-quality Bluetooth codecs and includes the high-performance ES9219 Quad DAC.
It can be considered an ultra-compact high-fidelity device with a power supply that utilizes a low-dropout regulator (LDO) to keep the floor noise level very low, in addition to features that block noise that may be introduced from the car's power system.
Without the need for elaborate connections to the car audio system, you can simply plug the compact SLASH4 unit into the USB power port and connect it to the car audio's AUX input with a 3.5mm stereo cable for instant use. This is the most appealing aspect.
If you want to upgrade the car audio system of an older model with a high-quality Bluetooth codec, I recommend considering the SLASH4 Bluetooth receiver from Do Blue. It offers an affordable price and easy installation.
Newly Released Do Blue SLASH4 - Hi-Fi Bluetooth DAC Receiver for Car Audio (brightandwiser.blogspot.com)
New DoBlue SLASH6 Bluetooth 5.1 Receiver with USB DAC AMP and Optical In/Out - while the old model was good, the new one is even better. (brightandwiser.blogspot.com)
Bright Sound In Mind (brightandwiser.blogspot.com)
