The Classé Sigma SSP is an AV-preamp targeted for audiophile music lovers who don't want to setup 2 different systems (one for audio, one for home cinema). It is optimized for very high quality on the stereo channels and somewhat less performance for the remaining surround channels: the stereo channel has both one balanced input and one balanced output (XLR) while the remaining analog IOs (2 x stereo in, 7.1 out) are single-ended (RCA). The specs are as follows (selected):
The unit I am testing is in fact a Sigma SSP (Mk1) which had been upgraded to Mk2. This involves the replacement of the board with the HDMI I/Os and the DSP doing the audio processing. Otherwise both models are identical. It runs with firmware version 2.0.0.29 (currently the newest).
I used a brand new RME ADI-2 PRO fs to feed the SSP with digital signals (SPDIF Coax and Toslink, USB and HDMI) and connected the XLR output of the SSP to the XLR input of the RME (one channel only). All internal processing in the SSP was disabled (no EQ, no tone control, nothing) and the inputs were set to pass through (no volume control). In this configuration the SSP delivered almost 14 dBu (ca. 3.8 V rms, very close to the SN input spec) output level with a 0 dBfs (-3dB rms) sinus. The analog input of the RME was set accordingly to +19 dBu with 5 dB higher gain, resulting in a full scale sensitivity of 14 dBu.
The RME was connected via USB to a Dell Latitude E7250 (Windows 10, RME ASIO driver) running on battery. I used RoomEq wizard v5.19 (REW) for all measurements, but for the jitter test and multitone I had to use foobar2000 to play wav files bit correct (verified by playing the specific test signals supplied by RME). The J-Test and multitone wavfiles were created with a DIY program running on Linux.
Just for the records: here is the loopback performance of the RME alone (XLR out to XLR in) at 14 dBu output level and 14 dBu input sensitivity. At 44.1 kHz samplerate and 24 bit, THD with 1 kHz sinus -3 dB rms (=0 dBfs), 32 FFT size, no averaging:
REW's distortion panel says this:
Sigma SSP via SPDIF Toslink
Let's start with THD, 44.1 kHz samplerate, 24 bit, 1 kHz sinus @ -3 dB rms (=0 dBfs), 32k FFT size, no averaging:
REW's distortion panel says this:
Beats me - but certainly not audible. Here is the same measurement with RME loopback:
This looks very clean, just some very tiny hash north of 10 kHz.
Next is IMD, 44.1 kHz samplerate, 24 bit, 19 + 20 kHz sinus @ -10 dB rms, 32k FFT size, no averaging:
REW's distortion panel says this:
Now J-Test, 44.1 kHz samplerate, 24 bit, 32k FFT size, no averaging:
Nothing to complain about, but let's see if averaging (32x) and higher FFT siźe (128k) reveal something:
Indeed there are some spurous signals but definitely not audible at all.
Sigma SSP via SPDIF Coax
THD, 44.1 kHz samplerate, 24 bit, 1 kHz sinus @ -3 dB rms (=0 dBfs), 32k FFT size, no averaging:
REW's distortion panel says this:
IMD, 44.1 kHz samplerate, 24 bit, 19 + 20 kHz sinus @ -10 dB rms, 32k FFT size, no averaging:
REW's distortion panel says this:
The numbers are (within the error margin) same as Toslink.
J-Test, 44.1 kHz samplerate, 24 bit, 128k FFT size, 32x averaging:
No real difference to Toslink.
Multitone, 192 kHz samplerate, 24 bit, 30 sinus signals, 128k FFT size, no averaging:
Nothing to worry about. Averaging does not reveal any more spurious signals.
Sigma SSP via USB
THD, 44.1 kHz samplerate, 24 bit, 1 kHz sinus @ -4 dB rms (=-1 dBfs), 32k FFT size, no averaging
I had to reduce the output level by 1 dB because at 0 dB there was significan distortion through clipping. This is probably a problem in the Windows 10 audio driver.
REW's distortion panel says this:
A bit more noise than SPDIF, otherwise the same.
IMD, 44.1 kHz samplerate, 24 bit, 19 + 20 kHz sinus @ -10 dB rms, 32k FFT size, no averaging:
REW's distortion panel says this:
There is seemingly more hash and noise, let's see with 32x averaging and 128k FFT size:
This is not noise. Performance is clearly not on the same level as SPDIF, but are we sure that the sum of all those spurious signals is audible?
J-Test, 44.1 kHz samplerate, 24 bit, 128k FFT size, 32x averaging:
This also is not noise, it's too regular. Lets spread the frequency axis:
Jep, not noise. Probably not audible though.
Sigma SSP via HDMI
A warning up front: The following measurements should be taken not with a grain, but with a bucket of salt:
THD, 48 kHz samplerate, 24 bit, 1 kHz sinus @ -4 dB rms (=-1 dBfs), 32k FFT size, no averaging
I'm not showing the numbers since they are not correct.
On a next shot I could try to burn the test signals on a CD and play them with my Bluray player (HDMI and SPDIF Coax).
IMD, 44.1 kHz samplerate, 24 bit, 19 + 20 kHz sinus @ -10 dB rms, 32k FFT size, no averaging:
IMD is good but there is also a lot of hash all over the full frequency range. Again no numbers.
J-Test, 44.1 kHz samplerate, 24 bit, 128k FFT size, 32x averaging:
Oh oh. Not sure whether the J-Test signal was played bit correct at all, so no judgement possible.
Conclusion
And one last point: Now that I've made my first full set of measurements I know how much work this is. I really don't know how Amir manages to publish almost one review per day. Lets all thank Amir for his daily work!
Frequency response: 8 Hz - 200 kHz < 1 dB (stereo digital bypass), 8 Hz - 20 kHz < 0.5 dB (all other sources)
Distortion (THD+noise): 0.0005% (digital source / bypassed analog source), 0.002% (processed analog source)
Maximum input level (single-ended): 2 Vrms (DSP), 4.5Vrms (bypass)
Maximum input level (balanced): 4 Vrms (DSP), 9 Vrms (bypass)
Maximum output level: 9 Vrms (single-ended), 18 Vrms (balanced)
Input impedance: 100 kΩ (single-ended), 50 kΩ (balanced)
Output impedance: 100 Ω (single-ended), 300 Ω (balanced)
Signal-to-noise ratio (ref. 4Vrms input, unweighted): 104 dB (bypassed analog source), 101 dB (processed analog source), 105 dB (digital source)
The unit I am testing is in fact a Sigma SSP (Mk1) which had been upgraded to Mk2. This involves the replacement of the board with the HDMI I/Os and the DSP doing the audio processing. Otherwise both models are identical. It runs with firmware version 2.0.0.29 (currently the newest).
I used a brand new RME ADI-2 PRO fs to feed the SSP with digital signals (SPDIF Coax and Toslink, USB and HDMI) and connected the XLR output of the SSP to the XLR input of the RME (one channel only). All internal processing in the SSP was disabled (no EQ, no tone control, nothing) and the inputs were set to pass through (no volume control). In this configuration the SSP delivered almost 14 dBu (ca. 3.8 V rms, very close to the SN input spec) output level with a 0 dBfs (-3dB rms) sinus. The analog input of the RME was set accordingly to +19 dBu with 5 dB higher gain, resulting in a full scale sensitivity of 14 dBu.
The RME was connected via USB to a Dell Latitude E7250 (Windows 10, RME ASIO driver) running on battery. I used RoomEq wizard v5.19 (REW) for all measurements, but for the jitter test and multitone I had to use foobar2000 to play wav files bit correct (verified by playing the specific test signals supplied by RME). The J-Test and multitone wavfiles were created with a DIY program running on Linux.
Just for the records: here is the loopback performance of the RME alone (XLR out to XLR in) at 14 dBu output level and 14 dBu input sensitivity. At 44.1 kHz samplerate and 24 bit, THD with 1 kHz sinus -3 dB rms (=0 dBfs), 32 FFT size, no averaging:
REW's distortion panel says this:
32768-point spectrum using Hann window and no averaging
Input RMS -3,1 dBFS, -3,1 dBC, -3,1 dBA
Distortion at 1.000,0 Hz, -3,1 dBFS based on 8 harmonics:
THD: 0,00016 %
N: 0,00041 %
THD+N: 0,00044 %
2nd harmonic 0,00011% 92 deg
3rd harmonic 0,00011% 8 deg
4th harmonic 0,000035% 91 deg
5th harmonic 0,000007% -123 deg
6th harmonic 0,000015% 94 deg
7th harmonic 0,000012% -166 deg
8th harmonic 0,000011% 63 deg
9th harmonic 0,000005% 154 deg
We cannot expect better performance than this, so we must at least reduce the results of the SSP by the corresponding results of the RME.Sigma SSP via SPDIF Toslink
Let's start with THD, 44.1 kHz samplerate, 24 bit, 1 kHz sinus @ -3 dB rms (=0 dBfs), 32k FFT size, no averaging:
REW's distortion panel says this:
32768-point spectrum using Hann window and no averaging
Input RMS -3,3 dBFS, -3,3 dBC, -3,3 dBA
Distortion at 1.000,0 Hz, -3,3 dBFS based on 8 harmonics:
THD: 0,00073 %
N: 0,0029 %
THD+N: 0,0030 %
2nd harmonic 0,00057%
3rd harmonic 0,00017%
4th harmonic 0,000047%
5th harmonic 0,00021%
6th harmonic 0,000035%
7th harmonic 0,00032%
8th harmonic 0,00013%
9th harmonic 0,00012%
This is not bad at all: - when we subtract the RME's THD (0.00016 %) from the SSP's THD (0.00073 %) we get a THD of 0.00058 % which is pretty close to the specified 0.0005 % and certainly within our error margin.
- Subtracting the RME's noise (0.00041 %) from the SSP's noise (0.0029 %) results in a noise of 0.0025 %. I am not sure if the subtraction is correct (regarding the stochastic nature of noise) and how to convert % into dB (a simple conversion, e.g. with Sengpiels dB calculator gives 92 dB for the SSP and 107 dB for the RME - values which I think may be too bad; the RME should deliver ca. 10 dB more, which then would also apply to the SSP). Maybe someone can shed some light here ...
Beats me - but certainly not audible. Here is the same measurement with RME loopback:
This looks very clean, just some very tiny hash north of 10 kHz.
Next is IMD, 44.1 kHz samplerate, 24 bit, 19 + 20 kHz sinus @ -10 dB rms, 32k FFT size, no averaging:
REW's distortion panel says this:
32768-point spectrum using Hann window and no averaging
Input RMS -7,6 dBFS, -18,6 dBC, -16,6 dBA
IMD is 0,00017 % for f1 = 19.000 Hz, f2 = 20.000 Hz
d2L: 0,00017%
The RME has IMD of ca. 0.0001 % in loopback, so this is pretty good. But again we see the wavey nature of the noise floor.Now J-Test, 44.1 kHz samplerate, 24 bit, 32k FFT size, no averaging:
Nothing to complain about, but let's see if averaging (32x) and higher FFT siźe (128k) reveal something:
Indeed there are some spurous signals but definitely not audible at all.
Sigma SSP via SPDIF Coax
THD, 44.1 kHz samplerate, 24 bit, 1 kHz sinus @ -3 dB rms (=0 dBfs), 32k FFT size, no averaging:
REW's distortion panel says this:
32768-point spectrum using Hann window and no averaging
Input RMS -3,3 dBFS, -3,3 dBC, -3,3 dBA
Distortion at 1.000,0 Hz, -3,3 dBFS based on 8 harmonics:
THD: 0,00073 %
N: 0,0030 %
THD+N: 0,0031 %
2nd harmonic 0,00057%
3rd harmonic 0,00021%
4th harmonic 0,000070%
5th harmonic 0,00025%
6th harmonic 0,000038%
7th harmonic 0,00027%
8th harmonic 0,000045%
9th harmonic 0,00016%
The numbers are the same as Toslink.IMD, 44.1 kHz samplerate, 24 bit, 19 + 20 kHz sinus @ -10 dB rms, 32k FFT size, no averaging:
REW's distortion panel says this:
32768-point spectrum using Hann window and no averaging
Input RMS -7,6 dBFS, -18,6 dBC, -16,6 dBA
IMD is 0,00019 % for f1 = 19.000 Hz, f2 = 20.000 Hz
d2L: 0,00019%
The numbers are (within the error margin) same as Toslink.
J-Test, 44.1 kHz samplerate, 24 bit, 128k FFT size, 32x averaging:
No real difference to Toslink.
Multitone, 192 kHz samplerate, 24 bit, 30 sinus signals, 128k FFT size, no averaging:
Nothing to worry about. Averaging does not reveal any more spurious signals.
Sigma SSP via USB
THD, 44.1 kHz samplerate, 24 bit, 1 kHz sinus @ -4 dB rms (=-1 dBfs), 32k FFT size, no averaging
I had to reduce the output level by 1 dB because at 0 dB there was significan distortion through clipping. This is probably a problem in the Windows 10 audio driver.
REW's distortion panel says this:
32768-point spectrum using Hann window and no averaging
Input RMS -5,3 dBFS, -5,3 dBC, -5,3 dBA
Distortion at 1.000,0 Hz, -5,3 dBFS based on 8 harmonics:
THD: 0,00073 %
N: 0,0037 %
THD+N: 0,0038 %
2nd harmonic 0,00052% -102 deg
3rd harmonic 0,00012% 51 deg
4th harmonic 0,00017% 73 deg
5th harmonic 0,000045% -107 deg
6th harmonic 0,000085% -172 deg
7th harmonic 0,00035% 177 deg
8th harmonic 0,00015% -146 deg
9th harmonic 0,00024% 174 deg
A bit more noise than SPDIF, otherwise the same.
IMD, 44.1 kHz samplerate, 24 bit, 19 + 20 kHz sinus @ -10 dB rms, 32k FFT size, no averaging:
REW's distortion panel says this:
32768-point spectrum using Hann window and no averaging
Input RMS -12,4 dBFS, -23,4 dBC, -21,4 dBA
IMD is 0,00068 % for f1 = 19.000 Hz, f2 = 20.000 Hz
d2L: 0,00068%
There is seemingly more hash and noise, let's see with 32x averaging and 128k FFT size:
This is not noise. Performance is clearly not on the same level as SPDIF, but are we sure that the sum of all those spurious signals is audible?
J-Test, 44.1 kHz samplerate, 24 bit, 128k FFT size, 32x averaging:
This also is not noise, it's too regular. Lets spread the frequency axis:
Jep, not noise. Probably not audible though.
Sigma SSP via HDMI
A warning up front: The following measurements should be taken not with a grain, but with a bucket of salt:
- I had to use 48 kHz samplerate because Windows 10 resampled all audio to 48 kHz. Hence no multitone (requires 192 kHz).
- I had to reduce the output level of all 0 dBfs signals by 1 dB because at 0 dB there was significant distortion through clipping. This is probably a problem in the Windows 10 audio/video driver.
- Even with 1 dB less signal level the distortion is much higher compared to SPDIF and USB, and it does not get smaller with smaller signal level. Maybe a result of truncation withput dithering? Who knows, maybe Mr. Gates ...
THD, 48 kHz samplerate, 24 bit, 1 kHz sinus @ -4 dB rms (=-1 dBfs), 32k FFT size, no averaging
I'm not showing the numbers since they are not correct.
On a next shot I could try to burn the test signals on a CD and play them with my Bluray player (HDMI and SPDIF Coax).
IMD, 44.1 kHz samplerate, 24 bit, 19 + 20 kHz sinus @ -10 dB rms, 32k FFT size, no averaging:
IMD is good but there is also a lot of hash all over the full frequency range. Again no numbers.
J-Test, 44.1 kHz samplerate, 24 bit, 128k FFT size, 32x averaging:
Oh oh. Not sure whether the J-Test signal was played bit correct at all, so no judgement possible.
Conclusion
- respectable performance both on SPDIF Coax and Toslink
- almost same performance via USB. Those results which are worse compared to SPDIF could be a result of the Windows OS.
- performance via HDMI is not clear - the bad results can be a result of the Windows OS.
However it is very easy to circumvent audio through HDMI. The HDMI inputs can be configured such that HDMI is used for video only and any other input can be used for audio. You may loose multi channel though - I'm not sure which surround audio formats can be transported through SPDIF.
And one last point: Now that I've made my first full set of measurements I know how much work this is. I really don't know how Amir manages to publish almost one review per day. Lets all thank Amir for his daily work!