![]() ![]() ![]() Fig.3, taken with 16-bit "digital black" data, shows that the noise continues to rise above the audioband, peaking at around 100kHz.įig.2 Echo Indigo IO, 1/3-octave spectrum of dithered 1kHz tone at -90dBFS, with noise and spuriae, 16-bit data (top), 24-bit data (bottom). ![]() The noise floor rises in level above the mid-treble, due to the noiseshaping used in the DAC chip to get sufficient resolution. Both spectra are commendably free from distortion and power-supply-related spuriae, and the increase in bit depth gives an increase in dynamic range of 10-12dB, suggesting DAC performance of around 18 bits. This is shown graphically in fig.2, which shows the spectrum of the card's output, derived with a swept 1/3-octave bandpass filter, while it decoded 16- and 24-bit data representing a dithered 1kHz sinewave at -90dBFS. Channel separation was superb, at better than 100dB between 100Hz and 8kHz, decreasing to 80dB/88dB L/R at 10Hz and 93dB at 20kHz (not shown).įig.1 Echo Indigo IO, frequency response at -12dBFS into 100k ohms, with 96kHz sample rate (right channel dashed, 0.5dB/vertical div.).Ĭommendably for its price, the Indigo IO's DAC offers better than 16-bit resolution. Driving the card with data sampled at 96kHz gave the response shown in fig.1 the output is down 1.5dB at 46kHz, suggesting an antialiasing filter that is well-behaved in the time domain. The frequency response was absolutely flat with CD data (not shown). The output preserved absolute polarity- ie, was noninverting-and the source impedance was less than 1 ohm across the audioband. Looking first at the Indigo IO's analog output, using WAV files played back with Bias Peak 4.0, the maximum output at 1kHz with the volume control at its maximum was to specification at 1.603V. All the tests were performed with the Echo Indigo IO soundcard installed in my 867MHz Apple TiBook. ![]()
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