Solid State Logic SSL 2 MKII vs. Topping Pro E2x2 OTG (Audio Interfaces) Comparison Review and Measurements

[jkim]

Well, it does show the digital input level and voltage :
4Vrms, -0.14/0-0.16dBFS for line input

View attachment 427686

Also, distortion is hardly increasing with level

View attachment 427687

To compare with Amir's results, you should switch to line input.

The distortion of the D50 III is vanishing low, well below -130dB, so that can't have much impact on what you see here, which is much higher. (Although the input impedance here is lower)

View attachment 427688

Oh I missed that on Amir's dashboard. But I DID use the line in (TRS) on E2x2. The only explanation is then the contribution of D50 III. Otherwise, I cannot explain...

By the way, my testing of D50 III with Cosmos ADC in Mono Mode is very close to yours even without a notch filter:

Here D50 III's harmonics are some dBs above the noise floor of E2x2 ADC (around -150 dB). This gives a perfect explanation to me.

 

[Rja4000]

I purchased the Topping E2X2 OTG some time ago, with the idea to measure it, but didn't find time so far.

Here is a good motivation

SINAD vs Level graph, various inputs
Input Gain = min
Source = Topping D50 III in Mono, balanced outputs, 5V range
(same signal to both E2X2 inputs)
D50 III Input from E2X2 TosLink digital output.

So 0dBFS on the X scale is around 5Vrms.
But actual voltage will vary, since the input impedance varies.
(I know. I should measure input level in Vrms. But sorry, it's late and I'm tired.)

As suspected by @Blumlein 88 , the line input is giving the "worst" results - at same or similar input level.
(Note that the line input may accept up to +24dBu or >12Vrms, and here I'm limited to 5V by the D50 III. For more in-depth testing, I'll have to use the RME)

Here is the SINAD for Mic input for -7dBFS output level (around 2.2Vrms), the max input level for the Mic input.

 

[jkim]

I purchased the Topping E2X2 OTG some time ago, with the idea to measure it, but didn't find time so far.

Here is a good motivation

SINAD vs Level graph, various inputs
Input Gain = min
Source = Topping D50 III in Mono, balanced outputs, 5V range
(same signal to both E2X2 inputs)
D50 III Input from E2X2 TosLink digital output.

So 0dBFS on the X scale is around 5Vrms.
But actual voltage will vary, since the input impedance varies.
(I know. I should measure input level in Vrms. But sorry, it's late and I'm tired.)

View attachment 427878

As suspected by @Blumlein 88 , the line input is giving the "worst" results - at same or similar input level.
(Note that the line input may accept up to +24dBu or >12Vrms, and here I'm limited to 5V by the D50 III. For more in-depth testing, I'll have to use the RME)

Here is the SINAD for Mic input for -7dBFS output level (around 2.2Vrms), the max input level for the Mic input.

View attachment 427881

This certainly gives us the big picture. So, around 2.2 Vrms into its mic input (at the min gain) is the best-case scenario. My mic input test was done at a very low level, making the SINAD much worse as it was noise-dominated. Sure, you tested at the min input gain at which the line in will accept higher voltage signals. In that case, it will be also limiting towards its best SINAD.

Now I better understand how to properly test an audio interface's ADC performance. I think it'll be an extensive test if we measure its IMD / THD+N vs. level at the min, middle, and max input gain positions for both line-in and mic inputs.

 

[Rja4000]

So, around 2.2 Vrms into its mic input is the best-case scenario

... below 5V.
Strictly speaking, we don't know yet what happens above 5V: at 12V on line input, SINAD might be better.

 

[jkim]

... below 5V.
Strictly speaking, we don't know yet what happens above 5V: at 12V on line input, SINAD might be better.

Right. But your results enable us to make some educated guess..

 

[jkim]

Source = Topping D50 III in Mono, balanced outputs, 5V range
(same signal to both E2X2 inputs)
D50 III Input from E2X2 TosLink digital output.

Oh, a quick question about your setting. Does the above mean that you used the cross-correlation method?

And why did you use E2x2 TosLink out?

 

[Rja4000]

Does the above mean that you used the cross-correlation method?

No, here I didn't.

The cross-correlation averaging method uses the differences between the 2 input channels - fed by the same signal- to "remove" the ADC noise impact.
It then allows to measure the DAC more accurately.
Here, we are measuring the ADC.

And, anyway, the Audio Precision APx500 Flex software doesn't support the cross-correlation averaging, to my knowledge.

And why did you use E2x2 TosLink out?

It is easier to use the Topping E2X2 ASIO driver to send the test signal to the DAC and also to measure the input signal.

As the APx500 Flex allows only one ASIO driver for both outputs and inputs, I would have to use ASIO4ALL otherwise. But I don't like ASIO4ALL, which can be a pain to setup, so whenever I can avoid it...

 

[jkim]

No, here I didn't.

The cross-correlated averaging method uses the differences between the 2 input channels - fed by the same signal- to "remove" the ADC noise impact.
It then allows to measure the DAC more accurately.
Here, we are measuring the ADC.

That is why I asked as we're testing the ADC. But then why sending a mono signal to both inputs of E2x2?

 

[Rja4000]

That is why I asked as we're testing the ADC. But then why sending a mono signal to both inputs of E2x2?

That's how I usually do it:
DAC Signal has lower noise when 2 channels are combined (merged), and, since we test the ADC, I prefer to send the exact same signal to both ADC channels.
But that's of course not critical.
That does increase the load for the DAC though.

I use a set of Pre-Built Y cables
- Cordial CFY 0.3m MFF
- Cordial CFY 0.3m FMM
and some adapters
Any brand/build would work, of course

https://www.musicstore.com/en_BE/EUR/Cordial-CFY-0-3-MFF-C-ble-adaptateur-Y-0-3-m/art-ACC0008354-000

 

[totti1965]

Introduction​

Reviewing these two devices started out from a simple motivation for replacing my dead E-MU 0404 USB. I am a long-time speaker DIY'er and the E-MU 0404 USB, a state-of-the-art device at its time, had served my needs for 16 years admirably. But then it suddenly died. After studying all audio interfaces tested by Julian Krause at his YouTube channel, I made a short list: Solid State Logic SSL 2 MKII and Topping Pro E2x2 OTG. Ordered the SSL. Loved its design and it seemed to be working fine. But I noticed distortion levels in acoustic and DAC measurements somewhat high---not great. So I ordered the Topping, too. Right after receiving it, however, I discovered the E1DA Cosmos ADCiso, and found it had been a hit in small DIY world. After seeing its amazing performance, I couldn't help getting it along with the Cosmos Scaler. I also needed a DAC for measurement tasks, so I ordered the Topping D50 III based on the ASR review.

To cut a long story short, I decided to measure these two audio interfaces to satisfy my own curiosity. But then noticed that the SSL 2 MKII, being relatively new on the market, has not been tested extensively except by Julian Kraus. Showing only the dynamic range and noise level, Julian's tests are not adequate. As you will see below, distortion performance turns out to be a key factor in a proper assessment of the SSL.

The primary focus of this review is on the devices' ADC performance (i.e., recording quality) though their DAC sections are briefly examined as well. The reason is that I believe recording/measuring must be the main reason for purchasing a USB audio interface. Note that Topping Pro E2x2 has also been reviewed by Amir here at ASR, the test results of which may not precisely match my reported ones---they are very well aligned with each other, though.

Measurement Setup​

• Signal generator: Topping D50 III as a USB DAC.
• AD converter: E1DA Cosmos ADCiso Grade A in Stereo Mode, and Cosmos Scaler as a buffer.
• Software: Paul Kane's Multitone Loopback Analyzer for most of the tests, and Room EQ Wizard. Whenever possible, results were cross-checked b/w two software packages.
• External, analog filters were not used in this test. I could have used a low pass filter to remove harmonics from test tones, or a notch filter to avoid ADC-induced harmonics.
• Nonetheless, I believe the comparison of the two devices should be informative because they were measured under exactly the same conditions. That is, cabling, input/output levels, and software settings such as sample rates, FFT sizes, FFT window types, averaging, etc. were all matched.
• All tested input/output connections were balanced.
• I made sure of using a powered USB hub since SSL 2 MKII is solely bus-powered.
• The "4K" effect of SSL 2 MKII was not tested. This function is just for fun experiments; it adds a huge amount of harmonic distortions to the input.

As a baseline, below is a 1 kHz sine tone FFT spectrum (96 kHz bandwidth) from the testing setup:
View attachment 427335

I could get better results (by 3 dB) from ADCiso's Mono Mode, but did not bother to use it---too lazy for cable swapping and additional measurements. Note that the results (20 Hz - 20 kHz) are still very close to Amir's or Rja4000's D50 III measurements, except that slightly higher harmonics must be due to no analog notch filter being employed.

Solid State Logic SSL 2 MKII​

Solid State Logic (SSL) is a British pro audio company. Though not as popular as Focusrite, Motu, RME, etc., it is a well-known brand in pro audio. The SSL 2 MKII is the company's entry-level 2-channel audio interface, an update of its predecessor SSL 2. There is a 2x4 variant, SSL 2+ MKII (update of SSL 2+), which adds 2 output channels and MIDI in/out. The SSL 2 MKII retails at US $230 and SSL 2+ MKII at US $300.

View attachment 427338
View attachment 427339
View attachment 427340

Intended for use on studio desks, its console-style design is very attractive. All switches, knobs, indicators, and input/output jacks are positioned well. The parts seemed to be of high quality and their operation feels great. Its case is a mixture of metal and plastic, and I loved its overall premium feel. Also very nice is a weighted base of its case giving stability on a desk. One important design choice is that it is to be entirely USB bus-powered.

View attachment 427341
View attachment 427343

Its double-sided PCB has ES9821Q as its ADC chip on the front side and ES9016K2M as its DAC chip on the back side. I had high hopes for its ADC performance as ES9821Q is ESS's 2nd best 2-ch ADC chipset next to the venerable ES9822PRO adopted in the RME ADI-2 Pro line and E1DA Cosmos ADCiso. On paper ES9821Q's DNR and THD+N numbers are only 5 dB worse than ES9822PRO's.

Topping Pro E2x2 OTG​

This is one of the audio interface models offered as Topping's first pro audio products. This OTG model is essentially the sams as the non-OTG variant that was reviewed at ASR, except it has an additional USB-C port that can be connected to a smartphone simultaneously with a computer, and an optical out as well as an additional analog AUX out on the back panel. The E2x2 OTG retails at US $199 and the non-OTG model at US $159.

View attachment 427345
View attachment 427346

Pictures are from the Topping Pro website---didn't have a chance to take pictures of its exterior (mine is the black version). Its build quality is good though I personally like the SSL's build more. The case is made of full metal (aluminum and steel) but sharp edges and corners do not feel sophisticated. Although it can be bus-powered, a separate power supply through its dedicated USB-C power port is recommended.

But I did take a picture of its interior:
View attachment 427348

Unfortunately, it is impossible to know which ADC and DAC chipsets this audio interfance is based on, because all the chips suspected to function as such have no markings, or markings masked. Why?

ADC Measurements​

First up is SSL 2 MKII's ADC results of a 1 kHz tone from D50 III fed into SSL's XLR TRS line input:
View attachment 427351
The noise floor must be largely limited by ADC as we know D50 III's noise floor is much lower and noise must be uncorrelated b/w DAC and ADC. What mainly affects SINAD should be harmonic distortions contributed by both DAC and ADC. Let's compare this to the results from Topping E2x2:
View attachment 427364

In terms of SINAD, the two devices are neck and neck though E2x2 has cleaner higher-order harmonics. It is interesting to compare the above results to amir's E2x2 measurements: they are very, very similar---even the higher H2 of Ch2 and higher H3 of Ch1---except harmonics are a bit higher in mine. It is easy to conjecture that the test tone from D50 III is contributing some harmonics.

Dynamic range is great for both devices:
View attachment 427352
View attachment 427365

As expected, DNR measurements are unaffected by the test tone because the signal must be basically free of harmonics at this low amplitude.

Frequency response was measured as a sanity check:
View attachment 427353
View attachment 427366

Also measured was their wideband ADC quality of a 10 kHz tone:
View attachment 427354
View attachment 427367

One may think a 10 kHz tone test is meaningless because harmonics being excited are beyond the audible range. But I consider it still informative. These help us better understand the following results of a sine tone sweep over frequencies.

View attachment 427355
View attachment 427368

These results, combined with the wideband FFT results, suggest that SSL 2 MKII's THD+N performance is dominated by THD whereas E2x2's THD+N is masked by N. In particular, the THD performance of SSL 2 MKII's ADC is not great at higher frequencies. Sure, fundamentals at 10 kHz and above may be fine, but how about 3k-7kHz tones? Undesirable. On the other hand, E2x2 exhibits substantially lower THD across all fundamental frequencies. Its THD+N for the 96 kHz bandwidth is masked by its ultrasonic noise (> 50 kHz).

SSL 2 MKII's relatively high distortion levels are further revealed in the following IMD vs. level sweep:
View attachment 427356
View attachment 427369
EDIT: Ignore the "IMD+N" curves---just look at IMD results. There seems to be something incorrect with the calculation of IMD+N in the software.

It turns out that the distortion of SSL 2 MKII's ADC rises greatly when the signals approach the amplitude of input sensitivity whereas E2x2 shows much milder effects of test tone levels. Note, here, that the input sensitivity includes the effect of the input gain which is set to -1.5 dBFS when a 1 kHz sine tone at 4.2 Vrms is fed (i.e., generator 0 dBFS = 4.2 Vrms sine tone = ADC -1.5 dBFS). In fact, THD vs. level sweeps told a similar story (not shown here as I forgot to save them).

Testing their microphone input was tricky because I was trying to mimic low-level microphone signals which resulted in noisy test tones. But the results are still interpretable:
View attachment 427358
View attachment 427370

It turns out that E2x2's ADC THD from its mic input is much lower than SSL 2 MKII's across all testing frequencies (20 Hz-10kHz fundamentals). E2x2's THD+N is completely masked by noise due to the compromised test tone quality. In hindsight I should've done this test differently to obtain a cleaner noise floor. Instead of lowering the test tones with external preamp attenuation, I could've simply used stronger test tones, increased the input sensitivity with the gain knob, and accepted some digital noise with attenuation on D50 III. Anyway, because we know both devices' noise performance belongs in the top tier according to Julian Krause's tests (w/ dScope M1), we can focus on their distortion performance.

DAC Measurements​

Let's look at their DAC performance:
View attachment 427359
View attachment 427371

On SSL 2 MKII I used a volume setting a little lower than its max volume to match the output voltage of E2x2 on its max volume. The higher THD from SSL doesn't look great.

How about IMD sweeps?
View attachment 427360
View attachment 427372

Topping is much better. No contest.

THD vs. frequency sweep:
View attachment 427361
View attachment 427373

Topping wins again.

Ultrasonic filtering at 44.1 kHz sample rate:
View attachment 427362
View attachment 427374

SSL wins here, but this test is not that critical.

Jitter tests:
View attachment 427363
View attachment 427375

Both are fine.

I did not test their headphone outputs. According to Julian Krause's tests, Topping has an excellent headphone amp, which is also backed by Amir's measurements, and SSL's headphone out is also nice within its limit of being bus-powered.

Conclusion​

I had high hopes for SSL 2 MKII because it adopts the ES9821 ADC chipset which is ESS's relatively new ADC solution. Not the level of ES9822PRO, but still excellent on paper. SSL 2 MKII's ADC performance, however, is not impressive. It shows problematic distortion behavior especially when it meets with strong input signals, which worsens with higher-frequency tones. The same goes for its DAC which is based on ES9016K2M. Distortion increases with output amplitude and frequency. In contrast, Topping E2x2 OTG does not exhibit such problems. I can easily recommend the Topping but can't SSL.

Then, why do we see this undesirable distortion behavior from SSL? I don't believe it extracts the full potential of its employed chipsets. My strong suspicion is that designers at SSL made some compromises to make it stably operate entirely bus-powered. It has to provide everything, including mic preamp, phantom power, over-4-volt line out, and relatively powerful headphone out. It does all of these solely bus-powered---I made sure of using a quality powered USB hub for this testing. I'm not sure if it's possible to achieve all these without making a compromise.

There are some quirks I do not like with the Topping, though. Its input gain control knobs are very sensitive at some positions, making it difficult to set levels. Its design feels less sophisticated than the SSL. I love the SSL's appearance and ergonomics. I would have preferred it if its performance had been on par with the Topping's. Practically, however, it is possible to use SSL 2 MKII within its limitation. If one makes sure of setting its gain to a lower position to keep recorded signals well away from the peak level, the recording quality should be fine with DNR somewhat compromised.

Thank you so much for this test! Would like to find many more modern audio interfaces (apogee etc.) here at audiosciencereview.com Analog to digital converting (ADC) is a wide field!

 

[palm]

I used a E-MU 0404 USB for several years, a firmware update introduced digital in clock locking issues, annoying but not a total dealbreaker for me. It’s really the lack of OS X drivers update that made me abandon it prematurely.
Before buying an RME ADI-2 DAC FS, I considered many interfaces but none were particularly convincing. I would avoid analog volume potentiometer for example, ideally it would have multiple stereo outputs to experiment with bass management, and built in routing features.

Thanks for the exhaustive test!

 

[lewdish]

It would be nice if Topping had an interface w/ 32 bit float

 

[AnalogSteph]

It would be nice if Topping had an interface w/ 32 bit float

Understandable, but honestly RME would make a better candidate first... at least they already have the DSP horsepower to be able to pull off a composite ADC. The component I would see Topping do well on would be the high dynamic range input stage required.

 

[morillon]

Introduction​

Reviewing these two devices started out from a simple motivation for replacing my dead E-MU 0404 USB. I am a long-time speaker DIY'er and the E-MU 0404 USB, a state-of-the-art device at its time, had served my needs for 16 years admirably. But then it suddenly died. After studying all audio interfaces tested by Julian Krause at his YouTube channel, I made a short list: Solid State Logic SSL 2 MKII and Topping Pro E2x2 OTG. Ordered the SSL. Loved its design and it seemed to be working fine. But I noticed distortion levels in acoustic and DAC measurements somewhat high---not great. So I ordered the Topping, too. Right after receiving it, however, I discovered the E1DA Cosmos ADCiso, and found it had been a hit in small DIY world. After seeing its amazing performance, I couldn't help getting it along with the Cosmos Scaler. I also needed a DAC for measurement tasks, so I ordered the Topping D50 III based on the ASR review.

To cut a long story short, I decided to measure these two audio interfaces to satisfy my own curiosity. But then noticed that the SSL 2 MKII, being relatively new on the market, has not been tested extensively except by Julian Kraus. Showing only the dynamic range and noise level, Julian's tests are not adequate. As you will see below, distortion performance turns out to be a key factor in a proper assessment of the SSL.

The primary focus of this review is on the devices' ADC performance (i.e., recording quality) though their DAC sections are briefly examined as well. The reason is that I believe recording/measuring must be the main reason for purchasing a USB audio interface. Note that Topping Pro E2x2 has also been reviewed by Amir here at ASR, the test results of which may not precisely match my reported ones---they are very well aligned with each other, though.

Measurement Setup​

• Signal generator: Topping D50 III as a USB DAC.
• AD converter: E1DA Cosmos ADCiso Grade A in Stereo Mode, and Cosmos Scaler as a buffer.
• Software: Paul Kane's Multitone Loopback Analyzer for most of the tests, and Room EQ Wizard. Whenever possible, results were cross-checked b/w two software packages.
• External, analog filters were not used in this test. I could have used a low pass filter to remove harmonics from test tones, or a notch filter to avoid ADC-induced harmonics.
• Nonetheless, I believe the comparison of the two devices should be informative because they were measured under exactly the same conditions. That is, cabling, input/output levels, and software settings such as sample rates, FFT sizes, FFT window types, averaging, etc. were all matched.
• All tested input/output connections were balanced.
• I made sure of using a powered USB hub since SSL 2 MKII is solely bus-powered.
• The "4K" effect of SSL 2 MKII was not tested. This function is just for fun experiments; it adds a huge amount of harmonic distortions to the input.

As a baseline, below is a 1 kHz sine tone FFT spectrum (96 kHz bandwidth) from the testing setup:
View attachment 427335

I could get better results (by 3 dB) from ADCiso's Mono Mode, but did not bother to use it---too lazy for cable swapping and additional measurements. Note that the results (20 Hz - 20 kHz) are still very close to Amir's or Rja4000's D50 III measurements, except that slightly higher harmonics must be due to no analog notch filter being employed.

Solid State Logic SSL 2 MKII​

Solid State Logic (SSL) is a British pro audio company. Though not as popular as Focusrite, Motu, RME, etc., it is a well-known brand in pro audio. The SSL 2 MKII is the company's entry-level 2-channel audio interface, an update of its predecessor SSL 2. There is a 2x4 variant, SSL 2+ MKII (update of SSL 2+), which adds 2 output channels and MIDI in/out. The SSL 2 MKII retails at US $230 and SSL 2+ MKII at US $300.

View attachment 427338
View attachment 427339
View attachment 427340

Intended for use on studio desks, its console-style design is very attractive. All switches, knobs, indicators, and input/output jacks are positioned well. The parts seemed to be of high quality and their operation feels great. Its case is a mixture of metal and plastic, and I loved its overall premium feel. Also very nice is a weighted base of its case giving stability on a desk. One important design choice is that it is to be entirely USB bus-powered.

View attachment 427341
View attachment 427343

Its double-sided PCB has ES9821Q as its ADC chip on the front side and ES9016K2M as its DAC chip on the back side. I had high hopes for its ADC performance as ES9821Q is ESS's 2nd best 2-ch ADC chipset next to the venerable ES9822PRO adopted in the RME ADI-2 Pro line and E1DA Cosmos ADCiso. On paper ES9821Q's DNR and THD+N numbers are only 5 dB worse than ES9822PRO's.

Topping Pro E2x2 OTG​

This is one of the audio interface models offered as Topping's first pro audio products. This OTG model is essentially the sams as the non-OTG variant that was reviewed at ASR, except it has an additional USB-C port that can be connected to a smartphone simultaneously with a computer, and an optical out as well as an additional analog AUX out on the back panel. The E2x2 OTG retails at US $199 and the non-OTG model at US $159.

View attachment 427345
View attachment 427346

Pictures are from the Topping Pro website---didn't have a chance to take pictures of its exterior (mine is the black version). Its build quality is good though I personally like the SSL's build more. The case is made of full metal (aluminum and steel) but sharp edges and corners do not feel sophisticated. Although it can be bus-powered, a separate power supply through its dedicated USB-C power port is recommended.

But I did take a picture of its interior:
View attachment 427348

Unfortunately, it is impossible to know which ADC and DAC chipsets this audio interfance is based on, because all the chips suspected to function as such have no markings, or markings masked. Why?

ADC Measurements​

First up is SSL 2 MKII's ADC results of a 1 kHz tone from D50 III fed into SSL's XLR TRS line input:
View attachment 427351
The noise floor must be largely limited by ADC as we know D50 III's noise floor is much lower and noise must be uncorrelated b/w DAC and ADC. What mainly affects SINAD should be harmonic distortions contributed by both DAC and ADC. Let's compare this to the results from Topping E2x2:
View attachment 427364

In terms of SINAD, the two devices are neck and neck though E2x2 has cleaner higher-order harmonics. It is interesting to compare the above results to amir's E2x2 measurements: they are very, very similar---even the higher H2 of Ch2 and higher H3 of Ch1---except harmonics are a bit higher in mine. It is easy to conjecture that the test tone from D50 III is contributing some harmonics.

Dynamic range is great for both devices:
View attachment 427352
View attachment 427365

As expected, DNR measurements are unaffected by the test tone because the signal must be basically free of harmonics at this low amplitude.

Frequency response was measured as a sanity check:
View attachment 427353
View attachment 427366

Also measured was their wideband ADC quality of a 10 kHz tone:
View attachment 427354
View attachment 427367

One may think a 10 kHz tone test is meaningless because harmonics being excited are beyond the audible range. But I consider it still informative. These help us better understand the following results of a sine tone sweep over frequencies.

View attachment 427355
View attachment 427368

These results, combined with the wideband FFT results, suggest that SSL 2 MKII's THD+N performance is dominated by THD whereas E2x2's THD+N is masked by N. In particular, the THD performance of SSL 2 MKII's ADC is not great at higher frequencies. Sure, fundamentals at 10 kHz and above may be fine, but how about 3k-7kHz tones? Undesirable. On the other hand, E2x2 exhibits substantially lower THD across all fundamental frequencies. Its THD+N for the 96 kHz bandwidth is masked by its ultrasonic noise (> 50 kHz).

SSL 2 MKII's relatively high distortion levels are further revealed in the following IMD vs. level sweep:
View attachment 427356
View attachment 427369
EDIT: Ignore the "IMD+N" curves---just look at IMD results. There seems to be something incorrect with the calculation of IMD+N in the software.

It turns out that the distortion of SSL 2 MKII's ADC rises greatly when the signals approach the amplitude of input sensitivity whereas E2x2 shows much milder effects of test tone levels. Note, here, that the input sensitivity includes the effect of the input gain which is set to -1.5 dBFS when a 1 kHz sine tone at 4.2 Vrms is fed (i.e., generator 0 dBFS = 4.2 Vrms sine tone = ADC -1.5 dBFS). In fact, THD vs. level sweeps told a similar story (not shown here as I forgot to save them).

Testing their microphone input was tricky because I was trying to mimic low-level microphone signals which resulted in noisy test tones. But the results are still interpretable:
View attachment 427358
View attachment 427370

It turns out that E2x2's ADC THD from its mic input is much lower than SSL 2 MKII's across all testing frequencies (20 Hz-10kHz fundamentals). E2x2's THD+N is completely masked by noise due to the compromised test tone quality. In hindsight I should've done this test differently to obtain a cleaner noise floor. Instead of lowering the test tones with external preamp attenuation, I could've simply used stronger test tones, increased the input sensitivity with the gain knob, and accepted some digital noise with attenuation on D50 III. Anyway, because we know both devices' noise performance belongs in the top tier according to Julian Krause's tests (w/ dScope M1), we can focus on their distortion performance.

DAC Measurements​

Let's look at their DAC performance:
View attachment 427359
View attachment 427371

On SSL 2 MKII I used a volume setting a little lower than its max volume to match the output voltage of E2x2 on its max volume. The higher THD from SSL doesn't look great.

How about IMD sweeps?
View attachment 427360
View attachment 427372

Topping is much better. No contest.

THD vs. frequency sweep:
View attachment 427361
View attachment 427373

Topping wins again.

Ultrasonic filtering at 44.1 kHz sample rate:
View attachment 427362
View attachment 427374

SSL wins here, but this test is not that critical.

Jitter tests:
View attachment 427363
View attachment 427375

Both are fine.

I did not test their headphone outputs. According to Julian Krause's tests, Topping has an excellent headphone amp, which is also backed by Amir's measurements, and SSL's headphone out is also nice within its limit of being bus-powered.

Conclusion​

I had high hopes for SSL 2 MKII because it adopts the ES9821 ADC chipset which is ESS's relatively new ADC solution. Not the level of ES9822PRO, but still excellent on paper. SSL 2 MKII's ADC performance, however, is not impressive. It shows problematic distortion behavior especially when it meets with strong input signals, which worsens with higher-frequency tones. The same goes for its DAC which is based on ES9016K2M. Distortion increases with output amplitude and frequency. In contrast, Topping E2x2 OTG does not exhibit such problems. I can easily recommend the Topping but can't SSL.

Then, why do we see this undesirable distortion behavior from SSL? I don't believe it extracts the full potential of its employed chipsets. My strong suspicion is that designers at SSL made some compromises to make it stably operate entirely bus-powered. It has to provide everything, including mic preamp, phantom power, over-4-volt line out, and relatively powerful headphone out. It does all of these solely bus-powered---I made sure of using a quality powered USB hub for this testing. I'm not sure if it's possible to achieve all these without making a compromise.

There are some quirks I do not like with the Topping, though. Its input gain control knobs are very sensitive at some positions, making it difficult to set levels. Its design feels less sophisticated than the SSL. I love the SSL's appearance and ergonomics. I would have preferred it if its performance had been on par with the Topping's. Practically, however, it is possible to use SSL 2 MKII within its limitation. If one makes sure of setting its gain to a lower position to keep recorded signals well away from the peak level, the recording quality should be fine with DNR somewhat compromised.

It remains possible for your specific use "acoustic " to hunt for a very very low price a 0404 in working order...
;-)

 

[ssashton]

It remains possible for your specific use "acoustic " to hunt for a very very low price a 0404 in working order...
;-)

Yeah I just purchased two of them and keep my laptop running windows 7, lol.

That said, Motu M4 looks like it would match or slightly exceed the 0404 performance without breaking the bank like RME.

 

[morillon]

Yeah I just purchased two of them and keep my laptop running windows 7, lol.

That said, Motu M4 looks like it would match or slightly exceed the 0404 performance without breaking the bank like RME.

emu's features were sufficient 16 years ago for your use...they are just as sufficient now... ;-)
(In addition, these old cards offer functions that are now hardly present, unless you move upmarket, such as digital input/output (the EMU coaxial and toslink)..sometimes very useful ;-) )

 

[Julf]

Maybe SSL was just trying to emulate the characteristics of the classical 1980's mixing consoles?

 

[fabriciom]

Whats the latency on the topping?

 

[L5730]

Not read through the comments, o just dropping something I recall when looking into lower-end interfaces.
An organisation did a recording test in which they played a passage of music out of the interface and back into itself and recorded the loopback result. They then took the recording and recorded the loopback of that. This continued to build up something like 100 or more generations of analogue loopback recording as a demonstration of the quality. Level matching was performed reasonably well.
Most interfaces just added noise and their nth generation recording subjectively sounded a little less immediate and tight compared to the original file. The SSL device(s) seemed to increase high frequency content, noticeably changing the overall sound of the recording.
The testers take away was that, whilst yes the nth recording showed obvious audible frequency changes, that was an extreme number of loopbacks, and over maybe 10-20, there was no appreciable difference in frequency response.

Interesting. I can't find the video or a link to this test.

 

[ssashton]

Not read through the comments, o just dropping something I recall when looking into lower-end interfaces.
An organisation did a recording test in which they played a passage of music out of the interface and back into itself and recorded the loopback result. They then took the recording and recorded the loopback of that. This continued to build up something like 100 or more generations of analogue loopback recording as a demonstration of the quality. Level matching was performed reasonably well.
Most interfaces just added noise and their nth generation recording subjectively sounded a little less immediate and tight compared to the original file. The SSL device(s) seemed to increase high frequency content, noticeably changing the overall sound of the recording.
The testers take away was that, whilst yes the nth recording showed obvious audible frequency changes, that was an extreme number of loopbacks, and over maybe 10-20, there was no appreciable difference in frequency response.

Interesting. I can't find the video or a link to this test.

I did that once with an adc and dac. After 10 times there was some roll off at 20hz and 20khz. It was about 0.3dB with one pass, but obviously 3db with 10 passes.