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Bitperfect playback on dongles?

Glitch

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I'm in the market for a DAC+HeadphoneAmp dongle since I primarily use my Android phone as a source. My current desktop brick DAC+Amp is fine but the hedonist in me wants to be able to bring it in bed without getting caught in wires like a fish.

My question is do these dongles output bitperfect signal without an analog pot volume control? I see some of them have a +- digital volume controls and I assume this is perhaps doing voltage regulation on the DAC chip which is fine. But the 2 dongles I'm most interested in - Hidizs S9 Pro and Qudelix 5K are attenuated by the phone volume controls and that makes me nervous. Currently I use the Hiby music player on Android which allows to output in Exclusive Mode (bitperfect) to a USB DAC but this mode disables the Android OS Volume Control and one has to attenuate with the knob on the DAC side. Now these buttonless dongles seem to have proprietary drivers so it's not unreasonable to assume that the driver can send the phone volume inputs to the DAC chip in Exclusive Mode but I just never operated one so I want to understand what it's doing.

I can definitely hear a difference between bitperfect Exclusive Mode and regular OS playback on Android. But I'd be happy to be proven a fool if somebody can show objectively that it's the same.
 

staticV3

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Ok there's a lot to unravel here:

-virtually all dongles have digital hardware volume control via UAC2 commands. Meaning that with a compatible OS or music player, you can send volume commands via the phone's rocker or a GUI, those are sent to the dongle, and it attenuates the signal accordingly via digital signal attenuation (->you lose bit depth)

-Android doesn't support UAC2 volume control by default, but there are Apps like Hiby, Neutron, UAPP that can do that. All other desktop and mobile OSs support UAC2 hardware volume by default.

-Those dongles with volume buttons also use digital volume control. Analog volume control is pretty rare in the dongle world, and for the most part limited to a high gain/low gain switch.

-digital volume attenuation with its reduction in bit depth is a complete non-issue if implemented properly. That's where letting the DAC chip handle the task via UAC2 comes into play. It is actually barely worse than an analog volume pot as can be seen from graphs posted by @mdsimon2 and in turn you get perfect channel matching and more flexibility.

-while I haven't tested Android's resampler and mixer for audio fidelity, I've personally experienced its terrible volume control whereas I got awful noises and a noise gate cutting into my music with volume set to almost zero. In my case, the solution was to keep Android at or close to 100% and let the dongle do the attenuation via UAC2. Same underlying principle (digital attenuation), but better implemented in the DAC chip vs in the OS. As such, I think there is value in bypassing the Android audio stack entirely if absolute fidelity is a concern.
 
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Glitch

Glitch

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Wow, thank you for the thorough and informative reply, that's exactly the information I was looking for!

Yeah, I'm fine with digital attenuation in the DAC, I really just want to bypass the Android audio stack because I can actually hear it (not as bad as Windows). DSPs can do complex filtering without signal degradation, when are Operating Systems going to figure it out? Good to know about UAC2, I'm fine with using a dedicated audio player app like HiBy just for this.

Another question - does Bluetooth bypass the Android mixer and resampler? Or does it have its own mixer, even tough I can't play 2 apps at the same time anyway? (I don't think that I can play 2 apps together in Android and it's still messing with the output). I'm aware that Bluetooth codecs compression is not bitperfect and Amir's endorsement of LDAC.

Finally, I may have found my insurance policy - an inline analog volume knob. Will this work between the headphones and the amp or is it only intended to sit between the DAC and the headphone amp?

61g0IxZxJdL._AC_SL1500_.jpg
 

DVDdoug

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Finally, I may have found my insurance policy - an inline analog volume knob. Will this work between the headphones and the amp or is it only intended to sit between the DAC and the headphone amp?
I don't recognize that. It could be made for line-signals or headphone signals. The voltages are about the same but the impedances are different.

In any case, it's probably worse than anything digital. A passive headphone volume control will put a resistance is series with the headphone and since headphone impedance varies over the frequency range, that changes the frequency response. And the left & right won't track perfectly. If it's active, all analog electronics introduce some noise. The noise might be inaudible, but it's still probably worse than anything digital.
 
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Glitch

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It's a passive "high-end step potentiometer" but no impedance value is listed.

I can live with digital attenuation if UAC2 works out.

Just to make sure I understand what you are saying, do you mean that the headphone has a specific impedance curve and the potentiometer another and when they combine that would affect the frequency response curve? Shouldn't the potentiometer impedance response be flat across all frequencies?
 

taudier

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I can definitely hear a difference between bitperfect Exclusive Mode and regular OS playback on Android. But I'd be happy to be proven a fool if somebody can show objectively that it's the same.
Are you sure the Plugins virtualizer/spatializer are not activated in the Hiby app ? :)

With an analog volume knob you also reduce the background noise which can be troublesome with iem.
 
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Glitch

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Are you sure the Plugins virtualizer/spatializer are not activated in the Hiby app ? :)
Exclusive Mode doesn't bypass the in-app EQ and PlugIns, it just routes the final output stream directly to the hardware.

With an analog volume knob you also reduce the background noise which can be troublesome with iem.
?? Did you mean {increase} the background noise? They advertise an audio grade pot with discrete steps, I'm sure it will be fine as far as noise is concerned.

----
Btw, I have the Dan Clark Aeon RT Closed cans, 13K Ohm.
 

taudier

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Exclusive Mode doesn't bypass the in-app EQ and PlugIns, it just routes the final output stream directly to the hardware.
Yes and Plugins virtualizer/spatializer are activated in the Hiby app by default, and you "definitely hear a difference".
?? Did you mean {increase} the background noise? They advertise an audio grade pot with discrete steps, I'm sure it will be fine as far as noise is concerned.

----
Btw, I have the Dan Clark Aeon RT Closed cans, 13K Ohm.
I mean reduce the background noise. A part of the bakground noise will be dissipated through the resistance of the analog knob. The problem with resistance analog knob is/can be the frequency response as DVDdoug talked about.

Dan Clark Aeon RT Closed are 13 ohm, not 13k, and they have a low sensitivity so you shouldn't have issue with background noise.
 
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staticV3

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Noise shouldn't be an issue, but output power might be.
At 13Ω the 5K can do 1Vrms via 3.5mm and 1.8Vrms via 2.5mm. With the RT Closed that's 97.4 and 102.5dB SPL max respectively.
No measurements exist for the S9 Pro yet, so can't make any predictions.

For the best chance at driving the RT Closed from a dongle, get an E1DA 9038S.
It has 2.9Vrms @13Ω @1%THD+N -> 106.6dB SPL.
That's almost double the perceived loudness vs 5K 3.5mm and 33% up on the 5K 2.5mm.
Sadly no built-in EQ though.
 

ZolaIII

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You can have digital volume control as usual (smartphone volume button's) and in 100 steps in HiBy Music by enabling it in: settings - USB audio settings (after you enable exclusive access).
Screenshot_20220406-113135.png
For other players with their own USBA 2.0 driver it will depend on implementation.
How good it feel (physically pressing those switches) will depend on the phone you use.
 

Vincent Kars

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I wouldn't worry to much about digital volume control.
In the past DAC's had a 16 bit register so if you reduce volume by a hefty 48 dB, you loose half of the bits

MSB LSB
1111111111111111
0000000011111111

As most DAC's today are 24 or even 32
111111111111111100000000
000000001111111111111111
Even with a 48 dB reduction you have a 16 bit sample unaltered in a 24 bit register.
 
OP
Glitch

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Noise shouldn't be an issue, but output power might be.
At 13Ω the 5K can do 1Vrms via 3.5mm and 1.8Vrms via 2.5mm. With the RT Closed that's 97.4 and 102.5dB SPL max respectively.
No measurements exist for the S9 Pro yet, so can't make any predictions.

For the best chance at driving the RT Closed from a dongle, get an E1DA 9038S.
It has 2.9Vrms @13Ω @1%THD+N -> 106.6dB SPL.
That's almost double the perceived loudness vs 5K 3.5mm and 33% up on the 5K 2.5mm.
Sadly no built-in EQ though.

Amir says the Qudelix 5K has an option in the app to enable 2Vrms output. It's got a battery after all.
 
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Glitch

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You can have digital volume control as usual (smartphone volume button's) and in 100 steps in HiBy Music by enabling it in: settings - USB audio settings (after you enable exclusive access).
View attachment 198003
For other players with their own USBA 2.0 driver it will depend on implementation.
How good it feel (physically pressing those switches) will depend on the phone you

OK yes, I figured out last night how to use the Hiby property Volume Control for Exclusive Mode and on initial listen it sounded good to me both in Hardware and Software mode but I haven't done extensive listening. It seems like Hardware mode refers to UAC2

Screenshot_20220406-105543.jpg



That lovely tactile satisfaction of an actual volume knob though.
I wish Amir would review more of the cheaper Fiio portable amps with volume knobs but the older tests don't instill a lot of confidence.
 

ZolaIII

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@Glitch I referred to UAC 2.0 with USBA 2.0.
Of course it won't work with DSD streams (nor Dolby's but they are almost not present on the platform anyway).
I did (listening to) but some time ago, don't use mobile DAC and even less trogh OTG cable this day's.
Well I have mob with nice tac-tile fead back volume switches (I use it for volume control of amplifier with big rotary knob because I like it more like that).
Anyway point is that you have nice granulated volume control that's already software implemented if that satisfy your needs (not necessarily wishes and dreams).
I hope you will find what makes you happy, have a nice time.
 

JanesJr1

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Noise shouldn't be an issue, but output power might be.
At 13Ω the 5K can do 1Vrms via 3.5mm and 1.8Vrms via 2.5mm. With the RT Closed that's 97.4 and 102.5dB SPL max respectively.
No measurements exist for the S9 Pro yet, so can't make any predictions.

For the best chance at driving the RT Closed from a dongle, get an E1DA 9038S.
It has 2.9Vrms @13Ω @1%THD+N -> 106.6dB SPL.
That's almost double the perceived loudness vs 5K 3.5mm and 33% up on the 5K 2.5mm.
Sadly no built-in EQ though.
Re the S9 Pro with the Aeon phones, I have that dongle with the Drop/DCA Aeon Closed X phones, which are the same hardware and specs as the RT Closed. I don't have measurements other than Amirm's reviews, but I have been much surprised at how well the S9 Pro, in balanced mode at least, handles these low impedance/ low sensitivity phones. Very clean, deep bass; neutral tonality; open, airy presentation (with my standard EQ for those DCA phones). (The S9 Pro also works well with high-impedance Senn HD6XX's.) Amirm also tried the S9 Pro in his review on this website with 25 ohm DCA Ether Cx phones, as well as the HD650's (same as HD6XX's), and described himself as delighted with the S9 Pro's performance in single-ended (not balanced) mode.

I would love to see an objective head-to-head of the S9 Pro with the E1DA 9038s (balanced), which I also own, or 9038d (single ended). (Amirm did review an earlier generation of the 9038 dongle.) The s9 Pro has more power in SE mode, the 9038s more in balanced mode. As usual, no figures on current, which is more important than power for the DCA Closed RT cans. It's subjective, but I always hear a clearer and more transparent presentation with the S9 Pro driving the DCA phones, even when I give a slight volume edge to the E1DA 9038s dongle. I know, subjective, not blind, but my only expectation was that the E1DA was more likely to edge out the S9 and every time I try it with my most-familiar reference recordings, the S9 wins my subjective contest. Both dongles competent, the Hidizs a bit better to me. I hope someone with technical chops can do a better, objective comparison, because there are not many dongles that produce as much power and/or operate in balanced mode as the Hidizs and E1DA dongles do.

In any event, I now use the S9 all the time when mobile, and it competes favorably with my Topping A50s desktop amp, which, with 2 volts DAC input, has almost 3 watts of power in balanced mode into 13 ohm DCA cans. Which still surprises me. The S9 got me mobile with difficult phones for the first time.

PS I just figured out that the measurements from Amir were for the S9, not the S9 Pro. I have the S9 Pro, and it has the headroom and neutral tonality I need for difficult headphones plus EQ preamp. SEE MY ADDTIONAL FINDINGS IN MY NEXT POSTING, BELOW.
 
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staticV3

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Amir says the Qudelix 5K has an option in the app to enable 2Vrms output. It's got a battery after all.
My numbers are with full output enabled. Just because the 5K can do 2/4Vrms at 300 Ohm, doesn't mean it can do the same at 13. Like every Amp, it has current constraints, resulting in less voltage at low impedances.
In case of the 5K, voltage drops from 4 to 1.8 and from 2 to 1 once loaded with 13 Ohm:
Qudelix 5K Max Vrms vs Load.png

BTW, those numbers come from Qudelix directly: https://www.qudelix.com/blogs/5k-dac-amp/power-budget
 

JanesJr1

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Afaik he only measured the Hidizs S9. Not the S9 Pro.
Just figured out that the figures for Amir were for the S9, not the S9 Pro, and staticV3 spotted it, too.

There is a review of the S9 Pro on the web with specs and measurements at https://hiendportable.com/hidizs-s9-pro-english-review . In the context of this discussion, I note the author's mention of a 90 mA limiter that pegs balanced output at 130 mW into 15 ohms and 230 mW at 33 ohms. There is also mention of higher temperatures at high volumes. I have used it a lot, including high volume, and have noticed at most mild warmth. That's with the unit enclosed in a plastic shell/clip supplied by the OEM plus one long side covered with velcro. In practical use, I don't see a temperature problem based on my experience.

However the measurements indicate the S9 Pro is well-powered to drive the DCA cans. I get the following figures; let me know if it doesn't look right. With sensitivity of 91 dB for the DCA Aeon RT, and 110 dB spl that calculates to required power of 80 mW (well below 130mW spec mentioned above), 1.06 volts (well below >2V measurement) and 75.6 mA current required (vs. 90 mW spec with limiter). So this would confirm the ability of the dongle to power the DCA phones up to 110 SPL in balanced mode; any higher SPL and the limits seem to be reached. 110 dB SPL is good for me, even as a peak!
 
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Glitch

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@staticV3 Hmmm, so at 13Ohms the Hidizs S9 will deliver around 1V in both UNBAL and BAL, the Qudelix 5K will be about the same in UNBAL but a few dB more in BAL?
 
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