The γ1 Modular Miniature DAC

Specifications and benchmarks

The tests were conducted using the following equipment:
  1. Tektronix TDS2014B 100MHz quad trace digital storage oscilloscope
  2. Fluke 187 digital multimeter
  3. Toshiba Satellite A65 laptop computer with Celeron 2.8GHz CPU and 768MB RAM
  4. M-Audio Firewire Audiophile mobile interface
  5. RightMark Audio Analyzer 5.5 software
  6. other custom test jigs, cables and software
The γ1 USB board and DAC boards tested were populated with the TPS79333 and TPS793475 LDO voltage regulators. The WM8501 DAC chip was used on the DAC boards. All other parts were as specified in the parts list. The analog outputs were loaded with 10KΩ resistors.

Digital inputs
Input connector type Coaxial RCA jack, DC-blocking capacitor and transformer coupled,
galvanically isolated (config A, E and F)
Optical Toslink fiber-optic receiver module (config A, E and F)
USB Mini-B, 5-pin (config A, B, C, D and F)
Data format Coaxial & Optical S/PDIF, AES3, IEC-60958, EIAJ CP1201 digital audio
USB USB 1.1 digital audio
Input impedance Coaxial 75Ω
Minimum digital input level Coaxial less than 200mVpp
Input word widths Coaxial & optical 16 or 24 bits
USB 16 bits
Sampling frequency Coaxial & optical up to 96KHz, auto-detect
USB up to 48KHz, auto-detect
Digital outputs
Connector type Coaxial RCA jack, DC-blocking capacitor and transformer coupled,
galvanically isolated (config C and F)
Optical Toslink fiber-optic transmitter moduie (config C and F)
I²S 5-pin header on USB board (config D only)
Data format Coaxial & Optical S/PDIF
I²S I²S
Output impedance Coaxial 75Ω
Digital output level Coaxial 500mVpp nominal, 75Ω terminated
I²S 3.3V TTL nominal
Analog output
Output connector type 3.5mm stereo mini jack (config A, B, E and F)
Output Level 1.6Vrms at 0dBFS
Output impedance Less than 3Ω
Number of channels 2
Frequency response
at -1dBFS		 Fs = 44.1KHz 0.8Hz - 20.8KHz, +0.2dB, -3.0dB
Fs = 48KHz 0.8Hz - 22.5KHz, +0.2dB, -3.0dB
Fs = 96KHz 0.8Hz - 48.0KHz, +0.2dB, -3.0dB
S/N ratio
at -1dBFS, RMS, 1KHz, A-weighted		 all modes 126dB
Noise level
RMS, 20Hz - 20KHz, A-weighted		 16 bits, 44.1KHz 93.8dB
16 bits, 48KHz 94.1dB
16 bits, 96KHz 95.5dB
24 bits, 44.1KHz 97.0dB
24 bits, 48KHz 97.1dB
24 bits, 96KHz 97.6dB
Total harmonic distortion
at -3dBFS, 1KHz		 16 bits, 44.1KHz 0.0010%
16 bits, 48KHz 0.0012%
16 bits, 96KHz 0.0020%
24 bits, 44.1KHz 0.0010%
24 bits, 48KHz 0.0011%
24 bits, 96KHz 0.0021%
Intermodulation distortion + noise
60Hz / 7KHz, 4:1		 16 bits, 44.1KHz 0.0059%
16 bits, 48KHz 0.0058%
16 bits, 96KHz 0.0051%
24 bits, 44.1KHz 0.0042%
24 bits, 48KHz 0.0044%
24 bits, 96KHz 0.0040%
Stereo crosstalk
at -1dBFS, 100Hz - 10KHz		 16 bits, 44.1KHz -92.1dB
16 bits, 48KHz -91.3dB
16 bits, 96KHz -91.3dB
24 bits, 44.1KHz -93.7dB
24 bits, 48KHz -93.6dB
24 bits, 96KHz -91.3dB
Power
Source USB power or external regulated 5V DC adapter,
auto-sensing, priority given to DC adapter
DC adapter connector type coaxial, 1.3mm center pin, center positive
Software
Computer host operating system for USB Linux, MacOS, Windows
No additional software driver required

Note: γ1 will not decode AC3, ADAT or other non-PCM, non-audio data streams.

RMAA test results

Several tests were performed, one with the M-Audio Firewire Audiophile mobile interface running in loopback mode to establish the baseline (lowest limit of measurement resolution). The coaxial input tests were done using the M-Audio Firewire Audiophile's S/PDIF output, while the USB input tests were done with the γ1 plugged directly into the host computer's USB port. The M-Audio Firewire Audiophile's analog input is used for recording in all tests. The "32 bits" results are actually in 24 bit mode but contained in 32 bit words.

Click on the following links to see the results.

Comments on the RMAA test results

γ1's measured frequency response is flat with extended bandwidth and minimal passband ripple. The noise floor is remarkably low, as are the THD and IMD distortion products. The stereo crosstalk is also miniscule throughout the audio band. These results are excellent and compare favorably to other far more expensive, larger DACs.

In fact, many of these results approach the measurement limits of the setup (see the M-Audio Firewire Audiophile's baseline data).

Oscilloscope waveforms

Some oscillogram waveforms of the γ1 DAC are shown below. All input waveforms are digitally generated on the computer. The 16 bit data are fed through the USB interface to the γ1, while the 24 bit data are through the M-Audio Firewire Audiophile's S/PDIF output and connected to the S/PDIF input of the γ1. A Tektronix TDS2014B digital storage oscilloscope is used to display the analog line output waveform.

The square wave response graphs show fast rise times, and exhibit the Gibbs Phenomenon ringing behavior typical of high performance DACs, and are well damped.

1KHz sine wave, at 0dBFS, 16 bit, 44.1KHz 10KHz sine wave, at 0dBFS, 16 bit, 48KHz
 
1KHz sine wave, at -60dBFS, 24 bit, 96KHz 1KHz square wave, at 0dBFS, 16 bit, 44.1KHz
 
1KHz square wave, at 0dBFS, 16 bit, 48KHz 1KHz square wave, at 0dBFS, 24 bit, 96KHz


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