1. B9Scrambler
    Radsone EarStudio ES100: Deserving of the Hype
    Written by B9Scrambler
    Published Oct 15, 2018
    4.5/5,
    Pros - Holy features Batman, esp. with the EarStudio app - 2.5mm Balanced and 3.5mm unbalanced outputs - Battery life - Small size - Price - Pick something
    Cons - Tiny, nondescript buttons that are easy to confuse for one another
    Greetings!

    Today we're checking out the ES100, a Bluetooth receiver from Radsone.

    Radsone is a consumer electronics and technology company based out of Seoul, Korea, founded in 2011. Their technology (https://www.radsone.com/technology) is used by some heavy hitters in the industry, like Audio Technica, LG, and Qualcomm, so you know they've got some serious talent under their belt.

    We're not here to talk about that though. No, we're here because of the ES100. This little Bluetooth receiver has been lighting up the online forums this past year. This device has garnered a lot of attention from the audio community for it's impressive combination of tech and features offered at a more than reasonable price.

    Let's take a closer look.

    IMG_3986.JPG IMG_4911.JPG IMG_4914.JPG

    Disclaimer:

    I reached out to Radsone to see if they'd be willing to send over a sample of the ES100 for the purposes of review. They said yes, as evidenced by the review you're reading. The thoughts and impressions within this review and my own based on my experiences with the ES100. They do not represent Radsone or any other entity. Should wish to pick one up, and you should if you enjoy Bluetooth devices, you can check it out here; https://www.radsone.com/earstudio. Make sure you scroll to the bottom of the page to ensure you're ordering through an authorized retailer.

    If you want a more technical look at this device, I HIGHLY recommend checking out this stellar review from yuriv on Head-fi: https://www.head-fi.org/showcase/radsone-earstudio-es100.23284/reviews

    Tested with device firmware version 1.4.2.

    Package Contents:

    Disregard the condition of the packaging in my pictures. Seems Canada Post had it's way with the ES100 during shipping...
    • ES100 Bluetooth Receiver
    • Micro USB cable
    • Quick start manual
    Specifications:

    Output RMS Power
    - 3.5mm Unbalanced: 1.1 V
    - 2.5mm Balanced: 2.2 V

    SNR* (1KHz, 20KHz AES17)
    - 3.5mm Unbalanced: 109dB (+2.8dBu)
    - 2.5mm Balanced: 110dB (+8.8dBu)

    Output Impedance
    - 0.5~1 ohm

    Bluetooth Range
    - 10 meters

    THD+N* (1KHz, 20KHz AES17)
    - 3.5mm Unbalanced: 0.0022%
    - 2.5mm Balanced: 0.0014%

    Support
    - LDAC, aptX-HD, AAC, aptX, SBC

    Battery
    - 14 hours

    Manual
    - https://docs.wixstatic.com/ugd/fb72a4_ca4675b20f6a48cf8da9e504c2f4dddc.pdf

    IMG_4916.JPG IMG_4920.JPG IMG_4921.JPG

    Build and Ergonomics:


    The ES100 is mostly plastic with a very simple, clean design and a professional silver on grey color scheme. Metal is used for the clip on the back, helping out with durability in the long run. The clip's clamping force was fine in my opinion, but I've seen others finding it a little on the weak side. Not an issue I had, but worth noting anyway. Seams between the component parts are quite visible but line up properly without any sloppy gaps, including around the micro-USB, 2.5mm balanced output, and 3.5mm unbalanced output. To the right of the volume rocker on one side is a small grill behind which is the microphone for phone calls and the ambient sound feature. To the left is the 3.5mm output. On the other side of the unit is a rocker button for skipping through tracks, a pause/play button, and the 2.5mm balanced output. The face of the unit looks like a plain grey slab, though when in use you find there is an LED ring hidden beneath. The LED ring performs a number of functions, besides telling you if the device is on or not, using green, red, or blue colorings. I didn't bother to memorize the various notifications, simply because it wasn't necessary. The ES100 is easy to use and works exactly as you would expect.

    The buttons used to interact with the ES100 are small and nondescript with limited physical feedback when pressed. I personally found myself routinely pressing the wrong thing, resorting to looking at the device most of the time to adjust volume, or swap tracks. This was even after a month of routine use, though I've gotten used to it by now. If Radsone ever decides to revise the ES100, I would love to see them change up the buttons so that they are easier to tell apart without looking, and provide a more prominent click when pressed. It's a simple quality of life thing. The device is fine to interact with as is, but it could be better with some minor revisions.

    Bluetooth:

    The ES100's Bluetooth performance is quite positive. Starting with connection strength, in regular use I didn't have to worry about device placement. It could be in a pocket, clipped to my sleeve or shirt collar, or in my hand and dropouts weren't a worry. It has a 30 foot range which is about standard, and like most devices with that rating can really only achieve it when unobstructed. I liked to use it when connected to my computer or LG G6. Those devices could be left on the living room table, and I would be free to walk nearly anywhere in the apartment without experiencing dropouts. Heading to my office or the front door would put two walls between myself and the device which would lead to stuttering, but the connection would hold. Overall connection strength is quite good.

    The ES100 can connect two two devices at a time. It works fine and has remained tied to my LG G6 and Asus FX53V without the need to re-pair throughout the duration of my testing. I'm not sure what Bluetooth codecs my laptop supports, but they're not fantastic as evidenced by the audio delay while watching videos. Connected to my LG G6 over aptX HD or LDAC (defaults to LDAC) there is no delay that I could notice, making for pleasant video
    experiences.

    IMG_4923.JPG IMG_4924.JPG

    Sound Quality:

    Sound quality, regardless of whether you're using the ES100 over Bluetooth or USB (16bit max via USB on anything but macOS), balanced or unbalanced, is excellent. The two AK4375a DAC/AMP chips from Asahi Kasei provide plenty of driving power along with a warm leaning and smooth but very resolving signature. Some might describe it as an analogue sound. Unlike other products with similar traits, I didn't find the ES100 restricted to earphones with certain signatures. Whether it was being paired with the neutral and very detailed Astrotec Delphinus 5 or smooth and bassy Meze 99 Neo, pairings always sounded great. It's a very versatile product, a quality aided greatly by it's low output impedance.

    The ES100 has almost completely replaced my other portable headphone amps (Walnut F1 and Auglamour GR-1). Not only does it sound better regardless of how you're opting to connect to your device, but its also smaller, lighter, and has a vastly longer battery life.

    Companion App:

    The Earstudio app for Android or iOS gives the ES100 a TON of extra versatility and is an absolute must if you want to get the most out of it.

    From the home screen you have a number of options. Swipe right and a menu pops out from the left containing a slew of options, like searching for a device to connect to, LED functions, the manual, factory reset, and much more. Closing that menu, from the main screen you can also select input to change the codec, buffer length, hands-free profiles, output via USB DAC, mess around with Radsone's HD Jitter Cleaner, and even check out measurement graphs showing off the ES100's single tone performance with a variety of cell phones. Under output you can optimize the quality of the sound being pushed out through the 3.5mm and 2.5mm TRRS ports. Under 3.5mm you can select either Normal or High Performance modes. The high performance mode reduces the output impedance by nearly half (~1ohm to ~0.5ohm) resulting in a cleaner sound. Under 2.5mm you can select from Normal or High Voltage modes. The High Voltage mode doesn't change performance and simply doubles the voltage from 3.2v peak-to-peak to 6.4v peak-to-peak allowing you to drive some pretty demanding gear. They even provide an explanation of why balanced is superior, namely it reduces noise ground noise providing a cleaner sound. Going back to the home screen, you can also adjust the analog volume and source volume. Under analog volume you can adjust each channel separately by up to 6dB, set the max volume limit, and even estimate how loud you are listening when using the ES100 as a headphone amp by entering the impedance and sensitivity of your headphones. Cool!

    Next up is the equalizer. You're provided a preamp which can be adjusted +12dB or -12dB. Then you have ten sliders for adjusting a variety of frequencies; 31.5, 63, 125, 500, 1k, 2k, 4k, 8k, and 16k. Below that you have 12 distinct preset EQ options like Classical, Jazz, and Bass Reducer, as well as four presets that you can save specific EQ settings too. They can be renamed as well, so you never have to guess which is being used to tame the aggressive treble peak on your HiFiMan RE800.

    Next up under Sound Control, you can adjust how aggressively the app will compensate for and remove digital noise via the DCT level. Crossfeed can also be adjusted. Note that these options will be disables if connected via LDAC as they are not supported. Further down you can apply one of four digital filters to the AK4375a DAC, and if you need, play around with the over sampling rate.

    Last up is the Ambient Sound feature. This is something I was surprised to see included and not mentioned anywhere on Radsone's site. Most companies brag about such a feature whenever possible. Turning Ambient Sound on uses the ES100's in-built mic to pic up and feed in outside noise so that you can still hear your surroundings. When using this feature outdoors, unless the earphones or headphones I was using were unusually naturally well-isolating, aided further with foam tips, Ambient Sound wasn't as helpful as I was hoping. If the mic sensitivity was left fairly low, it didn't pick up important noises. Increasing the mic's sensitivity enough so that it would pic up sounds a decent distance away also resulted in every little brush and scrape against my clothes to be picked up leading to a very noisy and unpleasant experience. I found it most useful indoors where I could set the ES100 down beside me in a stationary position.

    As mentioned before, the app is filled to the brim with features and functionality and it really lets you tailor the ES100 to suit you and your listening behaviours and preferences. I imagine they put a ton of time into it, and it absolutely paid off. Best of all, if you're like me and are still learning the ins and outs of audio terminology and what does what, just click the numerous question marks to the right of most features for well written descriptions of what they do, why they're important, and how to use them. Odd as it is, it one of my favorite parts of the app.

    Screenshot_2018-09-20-16-28-01.png Screenshot_2018-10-15-17-45-03.png Screenshot_2018-09-20-16-28-40.png Screenshot_2018-09-20-16-28-34.png Screenshot_2018-10-15-17-46-57.png Screenshot_2018-10-15-17-46-10.png

    Final Thoughts:

    If you're a fan of high quality, portable audio and have been holding off on getting into wireless due to questionable audio quality, you're safe to dive in with the ES100. If you enjoy cool tech and love messing around with apps and features and fine tuning your audio experience, this is a great product for you. You can tweak until your heart is content. If you are the exact opposite and want something simple and easy to use, forgo the app and run the ES100 as a bare bones Bluetooth receiver. You'll still have an awesome time. This is great product for pretty much anyone. If I were to complain about anything, it would be the tiny, nondescript buttons that can be difficult to tell apart, something that will no longer be an issue once you have used to device for a while.

    At only 99.00 USD, the ES100 is beyond being an easy recommendation to any fan of portable audio. I don't say this often, but it lives up to the hype. Great job Radsone. Seriously.

    Thanks for reading!

    - B9Scrambler
      thejoker13, ngoshawk, Lurk650 and 4 others like this.
    1. antdroid
      This is the best portable solution on the market in my opinion. Does it all and sounds great.
      antdroid, Oct 16, 2018
      B9Scrambler likes this.
    2. B9Scrambler
      I haven't tried any of the direct competition, yet, but I can't image they'd be any better. This thing is amazing, lol.
      B9Scrambler, Oct 16, 2018
  2. Jaywalk3r
    This little thing is awesome!
    Written by Jaywalk3r
    Published Oct 14, 2018
    5.0/5,
    Pros - Supports multiple BT codecs
    Sufficient volume without getting near max
    2.5mm "balanced" dual-mono output
    EQ interface is quite good
    App or HW control
    Cons - App has a few bugs (but is still very usable)
    Volume changes lag volume adjustments by a second or two.
    I bought this to increase the convenience level of my Ety ER4XR. I have previously used (and abused) extensively the Samsung HS3000. What I wanted for my Eties was something like the HS3000, but with more power. The device I received exceeded all expectations.

    The app is pretty good. It provides many customizable options, while allowing many to be turned off for those who prefer to keep things simple. It's not without bugs, but I haven't encountered anything serious.

    The Ambient Sound feature is interesting, pumping ambient sound into the earphones, eliminating the need to remove good sealing IEMs in some cases, such as to hear an announcement on mass transit.

    Being able to control the ES100, not just the source material, from my phone is very convenient.

    The EQ supplements the nearly-missing EQ functionality of the iPhone's Music app nicely. The interface is intuitive and easy to use.

    Provided the codec is supported at both ends, the ES100 allows the user to force use of a particular BT codec.

    Perhaps the most underrated feature is the feature that allow the device to stop taking further charge after the battery reaches 80-90 percent capacity. Completely charged is a very stressful state for lithium ion batteries, so this feature could potentially extend the useful life of the device.

    The ES100 does everything I hoped, and more. Most importantly, it allows me to listen with my wired headphones, while using my phone without any cables, without any noticeable SQ deficiencies or unreasonable volume limitations imposed by the amp.
  3. yuriv
    Cute little portable equalizer
    Written by yuriv
    Published Sep 4, 2018
    4.0/5,
    Pros - Built-in 10-band graphic equalizer
    Stable Bluetooth connection
    Multipoint Bluetooth connections
    Latency isn’t too high.
    Mic turns any headphone into a Bluetooth headset for making calls.
    Mic can be set to let outside sound in.
    Analog volume control makes background hiss inaudible.
    Analog volume control can make fine volume adjustments (0.5 dB steps).
    Low output impedance
    2.5 mm jack doubles the voltage output by bridging the amplifiers.
    AptX, AAC, and other advanced codecs.
    Cons - No parametric equalizer
    The crossfeed could be better.
    They could have included accessories that make it more convenient to use.
    Unless otherwise noted, I’m writing about my experience with firmware version 1.3.2 and iOS control app version 1.7.2 - 1.7.5. I first wrote about my experience with the ES100 and firmware version 1.2.1 in this thread, with some basic audio measurements. I’ve been using the ES100 on and off for the last few months, and I’ve been keeping notes. I put together my observations here.

    Sony MH755 with ES100.jpg
    Radsone EarStudio ES100 with Sony MH755​

    I picked up the Radsone EarStudio ES100 back in May because it gives my portable devices a system-wide equalizer. If iOS and Android had something like Equalizer APO or eqMac2 without having to root or jailbreak, I probably wouldn’t have bought one. It’s the closest thing to an ultra-portable equalizer today. Remember these?

    Well, the ES100 is the modern version, except that audio comes in via Bluetooth or USB instead of a line input. But it also does a lot more while being a lot smaller. Besides being a compact graphic EQ, it’s a versatile Bluetooth receiver that you can clip on a belt or even a headphone’s headband. If there are other super compact equalizers out there, Bluetooth or otherwise, I’d like to know about them.


    What it is
    The EarStudio ES100 is a very small Bluetooth receiver and USB DAC with headphone output. It has an all-plastic exterior that feels cheaply built at first because it’s very light. On the sides are volume up/down, next/previous track controls as well as a play/pause/on/off button. The rest of the controls are in the iOS or Android companion app.

    It comes with the standard 3.5mm headphone jack, but there’s also a 2.5mm TRRS output that doubles the output voltage by bridging the amplifiers. On the front is a single ring-shaped status LED, and on one of the short sides is a micro USB port for data and charging.


    Bluetooth receiver operation
    The ES100’s Bluetooth connection has remained stable in the few months that I’ve had it. It has AptX and AAC, which are good enough for me. The likelihood of hearing offensive lossy compression artifacts is very low, especially with AAC. Other advanced codecs like AptX HD and LDAC are also supported, but low latency AptX LL is missing from the list on the product page.


    List of codecs.png
    List of supported codecs​

    When playing software synthesizers on an iPad, there is considerable lag. I don’t know how well the ES100 will work with some games. For video, the worst Bluetooth audio sync that I’ve heard is in the iOS YouTube app. There are a few audio/video sync test videos on YouTube that give you an idea of how much latency there is. With the ES100, it seems to be a little over 100 ms, which is not as bad as it is on my other Bluetooth devices: it’s in the same ballpark as the Airpods, and much better than my Bose QC35 and Jaybird Freedom. A work-around for iOS is to play the same YouTube video in Safari, where the audio is more in sync. Other iOS apps (like Netflix) fare better than YouTube. In Windows 10 or MacOS, YouTube audio/video is more in sync than in the iOS app.


    Buffer length.png
    Buffer Length adjustment​

    The user has some amount of control over the latency, which can be reduced with a shorter buffer. The tradeoff is in reliability—with a shorter buffer, audio drop-outs are more likely.

    The ES100 supports multi-point connections. It can remember several paired devices and connect to two of them simultaneously. It’s convenient because I don’t have to fiddle with the Bluetooth settings on my phone, tablet, or laptop when I want to switch between any two of them.

    Another useful feature is the built-in microphone, which allows hands-free phone calls even with headphones that don’t have a built-in mic. The call quality depends on the placement of the ES100. It worked fine when it was clipped to the top of my shirt, but people I talked to said that they could hear me more clearly when I used the Airpods or the Jabra Elite 65t. When the ES100 was clipped to my belt, they said that they couldn’t hear me well at all.

    Ambient sound.png
    Ambient Sound​


    The microphone can also be used to let you hear more of the outside. Radsone calls this feature Ambient Sound, and it comes in handy when you want to be more aware of your surroundings. It’s also convenient when you want to hear people and you don’t want to go through the hassle of removing and reinserting a highly-isolating, deep-insertion IEM like an Etymotic. The track advance button can even be configured to turn Ambient Sound on and off, so you don’t have to whip out your phone and look for the right page in the control app.


    USB Audio
    The ES100 works as a USB Audio Class 1.0 interface in MacOS and recent Windows 10 updates, so no drivers are needed. The operation is locked at 48 kHz sample rate and 16 bits per sample. In Windows 10, for example, you can’t select any other sample rate or bit depth. All other options are unavailable. This means 16/44.1 CD-quality audio (and any other format) is sample-rate converted to 16/48. The SRC math seems to be working just fine. I didn’t hear any problems playing back 16/44 audio, and my measurements back in May didn’t reveal anything out of the ordinary with 16/44 wav files.


    Analog volume control and background noise level

    Analog and digital volume controls.png
    Analog and Digital Volume Controls​

    As you can see from the screenshot above, there are two volume controls. Most of the time, it’s best to keep the digital volume at maximum, and just control everything using the analog volume control. The advantage of doing this: decreasing the analog volume also decreases the background noise coming from the audio jack. This keeps the background hiss low, even inaudible, when using sensitive IEMs. I tested a Logitech UE600vi, which has above average sensitivity even among balanced armature IEMs. With the analog volume at 0 dB, the background hiss is quite loud. But you wouldn’t be listening to music at a crazy level like that with the UE600vi. With pop music, a comfortable level for me is around -36 dB on the analog volume control. It’s higher for classical music—maybe as much as -24 dB for quiet tracks. At that level, I can’t hear any background hiss from the ES100, even with a digital silence wav file.
    [​IMG]
    Noise level in dBV, into 16-ohm load on both channels​

    This makes the ES100 only the second Bluetooth device I’ve heard that’s completely silent. (I can’t hear any hiss from my Airpods either.) The physical volume up/down buttons on the ES100 control the analog volume, so it behaves differently in Apple devices than other Bluetooth headphones. In iOS, a Bluetooth device’s physical volume controls normally control the iPhone’s or iPad’s system volume. Not so with the ES100, and that’s a good thing because it gives you fine control: +/- 0.5 dB steps, unlike the very course adjustment in iOS.


    Output impedance, distortion under load
    When I measured my unit back in May, I found the audio output to be clean enough, even with the dummy load—16 ohms resistive, like the typical dynamic-driver IEM. I also verified the claimed 1-ohm output impedance. Since then, the app seems to have made another feature available: high current mode, which parallels two output stages and cuts the output impedance to 0.5 ohms.


    Audio output mode.png
    Audio Output Mode​

    With a high impedance load, the ES100 starts to clip when the analog volume is around +2 dB. With high current mode and a 16-ohm resistor on each channel, it clips earlier:


    High Current, 16-ohm load, +1 dB.png High Current, 16-ohm load, +1.5 dB.png High Current, 16-ohm load, +2 dB.png
    ES100 playing 0 dBFS 1 kHz sine, 3.5 mm jack, voltage into 16-ohm load on each channel: analog volume control at +1 dB, +1.5 dB, and +2 dB, respectively.​


    Here’s how much the output voltage drops when a 16-ohm load is connected to each channel:


    Normal, no load, -13 dB.png Normal, 16-ohm load, -13 dB.png
    ES100 playing 0 dBFS sine, 3.5 mm jack, analog volume control at -13 dB: open circuit voltage, voltage into 16-ohm load on each channel, respectively.​

    Do the math: www.wolframalpha.com/input/?i=0.198+*+16%2F(R+%2B+16)+%3D+0.192

    What’s strange is that I’m getting the same or better results when I leave it on normal mode. It looks like high current mode is on regardless of the setting in the app.


    The main feature: the equalizer
    With my collection of headphones and IEMs, the ES100 plays with low enough noise and distortion that I don’t have to worry about them. The only concern left is a big one, and it is really where the ES100 distinguishes itself from similar products. Many folks don’t want to admit it—that once you take care of noise, distortion, and lossy compression artifacts, it is the frequency response that determines the sound quality. The behavior in the time domain (e.g., the impulse response, the step response, square waves) is characterized by the system’s magnitude and phase response.

    This is why I was looking for an ultra-compact equalizer that can give my mobile devices a system-wide equalizer without rooting or jailbreaking. Here’s a sample of what the ES100’s 10-band EQ can do:

    [​IMG]
    -6 dB at 31.5 Hz, 1 kHz, and 16 kHz

    [​IMG]
    +3 dB at 2 kHz, 4kHz​

    This EQ can make many cheap headphones and IEMs sound good. Here’s an example: the Skullcandy Jib plays with low distortion, but its frequency response makes it sound like mud. Have a look: +8 dB at 200 Hz, and +11 dB at 100 Hz, relative to 1 kHz with the response still rising. It’s also missing a lot of information above 10 kHz:


    Skullcandy Jib FR.png
    Skullcandy Jib frequency response before EQ​

    Here’s the result with the ES100’s equalizer:

    Skullcandy Jib after EQ.png
    Skullcandy Jib response after EQ. 2017 Harman Target for IEMs shown in gray.

    Skullcandy Jib EQ.png
    EQ for Skullcandy Jib​

    The Jib has low enough distortion that it can handle a boost in the treble, and with the sliders shown in the picture, the ES100 gets the Jib’s response close to the 2017 Harman target for IEMs. It’s a good starting point for further adjustments. Me, I prefer less bass and a little bit more above 10 kHz. But even before that, the result already sounds very good IMO—better than many IEMs that cost more than the ES100 itself. This shouldn’t come as a surprise to anyone; for years, people in this forum have been writing about how a carefully-tuned EQ can make dirt cheap IEMs sound like a million bucks.


    Skullcandy Jib with ES100.jpg
    ES100 with Skullcandy Jib​



    Here’s another example—this time with a Sony MH755, a $6 IEM that already sounds very good without EQ:

    Sony MH755 sample 2 FR.png
    Sony MH755 frequency response before equalization


    Sony MH755 after EQ and channel trim.png
    Sony MH755 frequency response after EQ. 2017 Harman Target for IEMs shown in gray.


    Sony MH755 EQ.png
    EQ for Sony MH755​

    I have several pairs of MH755 and MH750 IEMs and I chose one that has a little channel imbalance. In the graph of the equalized response above, notice that the left and right channels are more closely matched. The ES100 has a nifty feature that lets you trim each channel, and I used it effectively here:


    Channel trim volume -0.5 dB.png
    Channel Trim on Device Volume Control page​

    The 10-band EQ works best with headphones that already have a smooth response, like the two IEMs above, or when there is a broad peak that lands close to one of the equalizer’s ten center frequencies. It's easy, for example, to give an Etymotic a little more bass. The EQ is more limited when you want to make the adjustment at a frequency that’s far from one of the graphic equalizer’s ten octave-spaced bands. For example, the Bose SoundTrue Ultra has a half-wavelength resonance that’s always at the same frequency because it has the same, repeatable, shallow insertion depth (if you could call it that). On my ears, it’s near 5.5 kHz—far from the ES100 EQ’s 4k or 8k bands.

    Even if you could guarantee that the adjustment frequency is correct, the equalizer still can’t handle high-Q resonances, which look like tall, narrow spikes in the frequency response. Here are some examples that can't really be fixed by the ES100's EQ without the help of acoustic methods:

    KZ ES4 FR.png
    KZ ES4 frequency response


    KZ ED16 FR.png
    KZ ED 16 frequency response​

    These two have the KZ house sound. The older KZ ATE also has that narrow spike near 8 kHz, depending on the insertion depth. For me this peak is not an artifact of measurement because I can clearly hear it in sine sweeps. Music sounds better when I use a parametric EQ to tame the bass and surgically flatten the peak with a narrow biquad filter. The ES100’s graphic equalizer, however, cannot effectively reduce the activation energy for these resonances.

    I wish Radsone had included a parametric equalizer with the ES100. Fewer filters bands would be needed and better results can be had for most headphones. If DSP resources are limited, then maybe one could choose to turn off the graphic equalizer to use the parametric EQ.

    It’s really a question of priorities. The ES100 has many features that made very little audible difference when I used them—the jitter reducer, the choice of reconstruction filter, the DCT filter, the DAC oversampling rate, and the additional codecs beyond AptX and AAC (although it is nice to have them). The EQ, on the other hand, has a huge impact on the sound. If there is an ES100 Mk.II in the works, my vote is for a more capable EQ, if it is impossible to update the current model’s firmware with one.


    The crossfeed is different?
    The ES100’s crossfeed has a strange implementation that’s not very effective. It seems to be very different from a Meier or Linkwitz crossfeed. When listening to speakers, each ear can hear a lot of low frequency information from the other channel. Therefore, the crossfeed should be stronger for low frequencies. This is not what I’m hearing from the ES100. Back in May, I got this response from the crossfeed:

    [​IMG]
    RMAA crosstalk measurements with crossfeed off and on.​

    Radsone’s implementation uses some inter-aural time difference, or ITD; i.e., the ES100 delays the sound on one channel before feeding it to the other one. I measured 2.5 ms before the crossfeed signal starts. You can figure out how far sound travels in that much time and decide for yourself if they got it right.

    So many things that make little audible difference are tweakable on the ES100. So why not something that can easily be heard, like a way to select the crossfeed implementation?


    Give me convenience or give me death
    Once the new toy syndrome wore off, I took the ES100 out of the house less often, and usually found myself grabbing something more immediate: Airpods, Jabra Elite 65t, Jaybird Freedom, Bose QC35. Their sound isn’t as good, but they’re good enough for enjoying music. Even when the ES100 was already in my pocket, I still went for the Airpods or the Jabras. Just open the case, put them in your ears, and you’re good to go: no cables to unwind, no connectors to plug in, and no power button to turn on. And when you’re done, just put them back in the case.

    Here’s one way to make the ES100 more convenient:

    ES100 with Philips SHP9500.jpg
    ES100 clipped to Philips SHP9500​


    I’ve often used the ES100 like this at home. Just turn it on and put on the headphones. Easy. I was lucky that I had a short cable at hand to make it work. The clip doesn’t go around the SHP9500’s headband, but It clamps tightly enough to stay put as long as you don’t shake your head too vigorously.

    It’s harder to find a short cable for other headphones:

    ES100 with Bose QC25.jpg
    Bose QC25 with its cable wrapped around the headband: ugly, but functional. A suitable short cable should work better.​


    ES100 with Audio Technica ATH-M40X.jpg
    Audio Technica ATH-M40X: none of my cables worked​

    A short cable and headphone mounting kit bundled in the box would have made the product more convenient to use. For IEMs, maybe a neckband or behind-the-head kit could work as an optional accessory.


    Conclusion
    The Radsone EarStudio ES100 is a useful little device. It’s also inexpensive. Audio performance is good enough for almost all listeners: It has low output impedance, it plays back audio with low distortion into realistic loads, its 2.5 mm jack provides double the voltage for insensitive headphones, its analog volume control makes the background hiss inaudible even when using sensitive IEMs, and it supports advanced audio codecs. But the killer feature, the one that improves the sound the most, is its equalizer.

    It’s just too bad that they didn’t make it even better by offering a fully parametric EQ as well. The crossfeed could use some help too. Also, a short cable kit to make headphone use easy and convenient would have been a nice addition. Despite these complaints, I know of no other product that does the same things while being so small and affordable. I want to see what they have planned for the next version.
    1. jeffhawke
      Excellent, very detailed review! However, considering the weight of the pros and the cons, especially considering the affordability, I would have given it a 4.5, if not a full 5 stars. I have one, and I enjoy it thoroughly.
      jeffhawke, Sep 4, 2018
    2. yuriv
      Thanks! It's clearly a positive review, but I'm leaving room for updates. Also it's only one data point. I'm somewhat surprised that no one else has left an extended review here, given the uniqueness of the product and the time that it has been out.

      Radsone hasn't released a firmware update since July. Wishful thinking has me hoping that they're working on something big...
      yuriv, Sep 5, 2018
    3. mhoopes
      Firmware v1.4.2 released 2018-09-17: https://www.radsone.com/earstudio
      USB DAC 44.1 KHz support for Windows is a nice addition; you can omit the 44.1->48 KHz resampling, which would apply to all Redbook CD audio files.
      dspGuru FAQ on resampling: https://dspguru.com/dsp/faqs/multirate/resampling/
      24-bit support on macOS gives the user some extra headroom for non-destructive software volume control for 16-bit file playback on your mac.
      mhoopes, Sep 24, 2018