Technics Grand Class SL-G700M2 Streaming SACD Player/DAC Measurements

Link: reviewed by Roger Kanno on SoundStage! Hi-Fi on September 15, 2023

General Information

All measurements taken using an Audio Precision APx555 B Series analyzer.

The Technics SL-G700M2 was evaluated as a digital-to-analog converter via the digital inputs and conditioned for 30 minutes at 0dBFS (2.2Vrms out) into 200k ohms before any measurements were taken.

The SL-G700M2 offers three digital inputs: one coaxial S/PDIF (RCA), one optical S/PDIF, and one USB. There are two line-level outputs (balanced XLR and unbalanced RCA) and one headphone output (1/4″ TRS labelled “PHONES”. There is a digital volume control for the headphone and line-level outputs. Comparisons were made between unbalanced and balanced line level outputs, no appreciable differences were seen in terms of THD and noise, but 1kHz FFTs are provided for both balanced and unbalanced outputs.

The SL-G700M2 offers a few features and settings. The following are the default settings used for the coaxial input, balanced line-level outputs, using a 0dBFS input, unless otherwise specified:

• Analog output level: fixed
• MQA processing: off
• Coherent Processing: on (forces a dedicated reconstruction filter)
• Filter: Mode 1, Mode 2, and Mode 3 are available (when Coherent Processing is off). These were evaluated for different parameters, such as phase, frequency, and impulse response (as indicated in the graphs below).

The analyzer’s input bandwidth filter was set to 10Hz to 22.4kHz for all measurements, except for frequency response (DC to 1MHz), FFTs (10Hz to 90kHz), and THD vs frequency (10Hz to 90kHz). The latter to capture the second and third harmonics of the 20kHz output signal.

The SL-G700M2’s digital volume control ranges from -99 to 0dB, in steps of 0.5dB. Channel-to-channel deviation proved average, at around 0.19dB throughout the range.

Volume-control accuracy (measured at line-level outputs): left-right channel tracking

Primary measurements

Our primary measurements revealed the following using the coaxial input and the balanced line-level outputs (unless specified, assume a 1kHz sinewave at 0dBFS, 200k ohms loading, 10Hz to 22.4kHz bandwidth):

*due to very low noise of DUT, analyzer self-noise has been removed from measurement to more accurately report value

Our primary measurements revealed the following using the coaxial input and the headphone output (unless specified, assume a 1kHz sinewave at 0dBFS, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

Frequency response vs. sample rate (16/44.1, 24/96, 24/192; Coherent Processing)

The plot above shows the SL-G700M2’s frequency response as a function of sample rate. The blue/red traces are for a 16bit/44.1kHz dithered digital input signal from 5Hz to 22kHz, the purple/green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and finally orange/pink represents 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same for the digital input—perfectly flat down to 5Hz. The behavior at high frequencies for all three digital sample rates is as expected, offering sharp filtering around 20k, 42k, and 82kHz (less than half the respective sample rate), although the 24/192 data shows softer attenuation around the corner frequency. The -3dB point for each sample rate is roughly 19.2, 41.7 and 81.3kHz respectively. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue, purple or orange trace) is performing identically to the right channel (red, green or pink trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

Frequency response vs. filter type (16/44.1)

The plots above show frequency-response for a 0dBFS input signal sampled at 16/44.1 for Mode 1  (blue), Mode 2 (red), Mode 3 (green), and Coherent Processing (pink) filters into a 200k ohm load for the left channel only. The graph is zoomed in from 1kHz to 22kHz to highlight the various responses of the three Mode filters. We can see Mode 1 and Coherent Processing offer essentially the same frequency response, with a -3dB point at 19.2 kHz, while Mode 2 is very close, with a -3dB point at 19.7kHz. It’s worth pointing out that the “knee” for these three filters occurs just past 16kHz, a frequency many audiophiles can no longer even hear. The Mode 3 filter behaves like a typical brickwall-type filter, with a -3dB point at 21.2kHz.

Phase response vs. sample rate (16/44.1, 24/96, 24/192; Coherent Processing)

Above are the phase-response plots from 20Hz to 20kHz for the coaxial input, measured across at the balanced output, using the Coherent Processing filter setting. The blue/red traces are for a dithered 16/44.1 input at 0dBFS, the purple/green for 24/96, and the orange/pink for 24/192. We can see that the SL-G700M2 does not invert polarity, with a worst-case phase shift of -140 degrees at 20kHz for the 16/44.1 data. Phase shift at 20kHz for the 24/96 and 24/192 input data are inconsequential, at about -5 degrees.

Phase response vs. filter (16/44.1)

Above are the phase response plots from 20Hz to 20kHz for a 0dBFS input signal sampled at 44.1kHz for the Mode 1 (blue), Mode 2 (red), Mode 3 (green), and Coherent Processing (pink) filters into a 200k ohm load for the left channel only. Predictably, the brickwall filter (Mode 3) yields the highest phase shift at around -180 degrees at 20kHz. The Mode 1 and Coherent Processing filters are identical, at -140 degrees at 20kHz, while the Mode 2 filter exhibits no phase shift throughout the audioband.

Digital linearity (16/44.1 and 24/96 data)

The graph above shows the results of a linearity test for the coaxial digital input (the optical input performed identically) for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the balanced line-level output of the SL-G700M2. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response is a straight flat line at 0dB (i.e., the amplitude of the digital input perfectly matches the amplitude of the measured analog output). The 24/96 input data is essentially perfect down to -120dBFS, while the 16/44.1 input data performed well, only over-responding by 4/2dB (left/right channels) at -120dBFS. The 24/96 data yielded such superb results that we extended the sweep down to . . .

. . . -140dBFS. Above we see that even at -140dBFS, the SL-G700M2 is only undershooting by -1 to -3dB. This is an exemplary linearity-test result.

Impulse response vs. filter type (Mode 1, Mode 2, Mode 3, Coherent Processing)

The graph above shows the impulse responses for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s), for one sample period then back to digital silence, fed to the coaxial digital input, measured at the balanced outputs, for Mode 1 (blue), Mode 2 (red), Mode 3 (green), and Coherent Processing (pink) filters into a 200k ohm-load for the left channel only. We can see that the Mode 1 and Coherent processing filters are nearly identical, with minimal pre-ringing and some post-ringing. The Mode 3 filter has no pre-ringing, but significant post-ringing, while the Mode 2 filter exhibits symmetrical pre- and post-ringing, as seen in a typical sinc function.

J-Test (coaxial input)

The plot above shows the results of the J-Test test for the coaxial digital input measured at the balanced line level output of the SL-G700M2. J-test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least-significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA (fundamental at 250Hz) down to -170dBrA for the odd harmonics.  The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to also show how well the DAC rejects jitter.

The coaxial input shows an average to mediocre J-Test result, with two peaks at the -130dBrA level clearly visible near 11kHz and 13kHz. This is an indication that the SL-G700M2 may be sensitive to jitter.

J-Test (optical input)

The plot above shows the results of the J-Test test for the optical digital input measured at the balanced line-level output of the SL-G700M2. The optical input shows essentially the same result as the coaxial input above.

J-Test (coaxial input, 2kHz sinewave jitter at 100ns)

The plot above shows the results of the J-Test test for the coaxial digital input (the optical input behaved the same) measured at the balanced line-level output, with an additional 100ns of 2kHz sinewave jitter injected by the APx555, which would manifest as sideband peaks at 10kHz and 14kHz without perfect jitter immunity. The results show visible sidebands at 10kHz and 14kHz, but at a relatively low -125dBrA. This is further evidence of the SL-G700M2’s average jitter immunity.

J-Test (coaxial input, 2kHz sinewave jitter at 600ns)

The plot above shows the results of the J-Test test for the coaxial digital input (the optical input behaved the same) measured at the balanced line-level output, with an additional 600ns of 2kHz sinewave jitter injected by the APx555. Here sidebands are visible at 10kHz and 14kHz again, but remain relatively low at -110dBrA. With jitter above this level, the SL-G700M2 lost sync with the signal.

Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (Mode 1)

The plot above shows a fast Fourier transform (FFT) of the SL-G700M2’s balanced-line level output with white noise at -4 dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 (purple/green), using the Mode 1 filter setting. There is a soft roll-off above 20kHz in the white-noise spectrum. There are absolutely no imaged aliasing artifacts in the audio and above the -135dBrA noise floor. The primary aliasing signal at 25kHz is at -35dBrA.

Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (Mode 2)

The plot above shows a fast Fourier transform (FFT) of the SL-G700M2’s balanced-line level output with white noise at -4 dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 (purple/green), using the Mode 2 filter setting. There is a soft roll-off above 20kHz in the white-noise spectrum. There are absolutely no imaged aliasing artifacts in the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is at -25dBrA.

Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (Mode 3)

The plot above shows a fast Fourier transform (FFT) of the SL-G700M2’s balanced-line level output with white noise at -4 dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 (purple/green), using the Mode 3 filter setting. There is a sharp roll-off above 20kHz in the white-noise spectrum showing the implementation of a brickwall-type reconstruction filter. There are absolutely no imaged aliasing artifacts in the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is at -100dBrA.

Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (Coherent Processing)

The plot above shows a fast Fourier transform (FFT) of the SL-G700M2’s balanced line-level output with white noise at -4 dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 (purple/green), using the Coherent Processing filter setting. There is a soft roll-off above 20kHz in the white-noise spectrum. There are absolutely no imaged aliasing artifacts in the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is at -35dBrA.

THD ratio (unweighted) vs. frequency vs. load (24/96)

The chart above shows THD ratios at the balanced line-level output into 200k ohms (blue/red) and 600 ohms (purple/green) as a function of frequency for a 24/96 dithered 1kHz signal at the coaxial input. The 200k and 600 ohms data are close throughout the audioband (within 10dB from 2kHz to 20kHz), which is in indication that the SL-G700M2’s outputs are robust and can handle loads below 1k ohms with no difficultly. THD ratios into 200k ohms ranged from 0.0002% from 20Hz to 500Hz, then up to 0.002% at 20kHz.

THD ratio (unweighted) vs. frequency vs. sample rate (16/44.1, 24/96)

The chart above shows THD ratios at the balanced line-level output into 200k ohms as a function of frequency for a 16/44.1 (blue/red) and a 24/96 (purple/green) dithered 1kHz signal at the coaxial input. The 24/96 data consistently outperformed the 16/44.1 data by 5-10dB from 20Hz to about 2kHz due to the inherently higher noise floor at 16 bits (i.e., the analyzer cannot assign a THD value below the noise floor). THD ratios with 16/44.1 data range from 0.0003% from 20Hz to 2kHz, then up to 0.002% at 16kHz. THD ratios with 24/96 data range from 0.0001-0.0002% from 20Hz to 2kHz, up to 0.002% at 20kHz.

THD ratio (unweighted) vs. output (16/44.1, 24/96)

The chart above shows THD ratios measured at the balanced output as a function of output voltage for the coaxial input into 200k ohms from -90dBFS to 0dBFS at 16/44.1 (blue/red) and 24/96 (purple/green). Once again, the 24/96 outperformed the 16/44.1 data, with a THD range from 0.1% at 200uVrms to 0.0001% at 0.5 to 2Vrms, while the 16/44.1 ranged from 2% down to nearly 0.0002%.

THD+N ratio (unweighted) vs. output (16/44.1, 24/96)

The chart above shows THD+N ratios measured at the balanced output as a function of output voltage for the coaxial input into 200k ohms from -90dBFS to 0dBFS at 16/44.1 (blue/red) and 24/96 (purple/green). The 24/96 outperformed the 16/44.1 data, with a THD+N range from 1% down to  0.0002% at 1.5-2Vrms, while the 16/44.1 ranged from 20% down to 0.002% at the maximum output voltage of 2.2Vrms.

Intermodulation distortion vs. generator level (SMPTE, 60Hz:4kHz, 4:1; 16/44.1, 24/96)

The chart above shows intermodulation distortion (IMD) ratios measured at balanced output for 16/44.1 (blue/red)  and 24/96 input data (purple/green), from -60dBFS to 0dBFS. Here, the SMPTE IMD method was used, where the primary frequency (F1 = 60Hz) and the secondary frequency (F2 = 7kHz) are mixed at a ratio of 4:1. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 16/44.1 data yields IMD ratios from 2% down to 0.002% at 0dBFS. The 24/96 data yields IMD ratios from 0.1% down to 0.0005% from -10 to 0dBFS.

FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced outputs into 200k ohm for the coaxial digital input, sampled at 16/44.1. We see signal harmonics at 2/3/5kHz, with the third harmonic (3kHz) dominating at -120dBra, or 0.0001%. There are also no power-supply noise peaks to speak of to the left of the main signal peak.

FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced outputs into 200k ohm for the coaxial digital input, sampled at 24/96. Due to the increased bit-depth, the noise floor is much lower compared to the 16/44.1 FFT at a very low -150 to -160dBrA. We see signal harmonics ranging from -120dBrA to -140dBrA, or 0.0001% to 0.00001%, all the way to 20kHz (and beyond). Here also, there are no power-supply noise peaks to speak of to the left of the main signal peak.

FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS, unbalanced output)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the unbalanced outputs into 200k ohm for the coaxial digital input, sampled at 24/96. We find small differences in the signal harmonic pattern here compared to the balanced inputs above. Here the second signal harmonic (2kHz) reaches -110dBrA, or 0.0003%, compared to -130dBrA, or 0.00003%, for the balanced inputs. There are also very low-level power-supply-related (or IMD) peaks on the right channel here to the left of the signal peak, from -140 to -150dBrA, that do not show up in the balanced outputs. 

FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced outputs into 200k ohm for the coaxial digital input, sampled at 16/44.1 at -90dBFS. We see the signal peak at the correct amplitude, and no signal harmonics above the noise floor within the audioband.

FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced output into 200k ohm for the coaxial digital input, sampled at 24/961 at -90dBFS. We see the signal peak at the correct amplitude, and extremely low-level signal harmonics (2/3/4kHz) at and below -150dBrA, or 0.000003%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, 16/44.1)

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the balanced output into 200k ohms for the coaxial input at 16/44.1. The input dBFS values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would yield 2.2Vrms (0dBrA) at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz), is perhaps barely visible above the noise floor from the right channel at -130dBrA, or 0.00003%, and the third-order modulation products, at 17kHz and 20kHz, are at -120dBrA, or 0.0001%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, 24/96)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the balanced output into 200k ohms for the coaxial input at 24/96. The input dBFS values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would yield 2.2Vrms (0dBrA) at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz), is at -130dBrA (right), or 0.00003%, and the third-order modulation products, at 17kHz and 20kHz, are at -115dBrA, or 0.0002%.

Intermodulation distortion FFT (coaxial input, APx 32 tone, 24/192)

Shown above is the FFT of the balanced line-level output of the SL-G700M2 with the APx 32-tone signal applied to the input. The combined amplitude of the 32 tones is the 0dBFS reference, and corresponds to 2.2Vrms into 200k ohms. The intermodulation products—i.e., the "grass" between the test tones—are distortion products from the amplifier and below the -145dBrA, or 0.000006%, level. This is a very clean IMD result.

Diego Estan
Electronics Measurement Specialist