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Playback formats on a TEAC UD-501 (TI PCM1795)

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This is interesting DAC with a reasonable price tag, looks nice and high quality components.

Since it also offers bypass of the digital interpolation filters with direct 32-bit 352.8/384 PCM input as well as DSD128 support with good set of analog filters (conversion mappings), I wanted to study which would be best way to play back RedBook content on it.

I have excluded time-domain behavior inspections from this post, because going to that domain while keeping the frequency-domain behavior optimal at the same time is complex topic with too many variables to be discussed in a single blog post. (read: brickwall filters vs non-brickwall filters) So I cover only frequency-domain inspection of various ways to reproduce RedBook.

First set of measurements I perform is a 44.1/24 PCM with sweep from 0 - 20 kHz and measure this on a wide-band spectrum analyzer using "peak-hold" to expose both reconstruction properties and quality as well as see patterns of ultrasonic output since this seems to be a hot topic. Optimal output would have just the 0 - 20 kHz output and nothing else in the spectrum.

Second set of measurements I perform is intermodulation distortion test with 19+20 kHz tones. Optimal output would have just the 19+20 kHz tones visible and nothing else.

Since the UD-501 defaults to "NOS" settings, I first measured it in this mode.
NOS mode, sweep 0-20 kHz
NOS mode, IMD 19+20 kHz
Since the wide-band output of the IMD test looked quite extraordinary, I reproduce it here...

Next was time to test the most ordinary setting, with digital filter set to "SHARP".
SHARP mode, sweep 0-20 kHz
SHARP mode, IMD 19+20 kHz

Then was the filter type many find better sounding due to shorter pre-/post-ringing, filter set to "SLOW".
SLOW mode, sweep 0-20 kHz
SLOW mode, IMD 19+20 kHz

Since there is the digital filter bypass, I wanted to test HQPlayer with a "short" filter and 384/32 output (TPDF dither).
NOS mode, HQPlayer short@384/32, sweep 0-20 kHz
NOS mode, HQPlayer short@384/32, IMD 19+20 kHz

Then the part I was most interested in, testing upsampling to DSD128 using modulator "5.1". I used analog FIR setting 4 in this test, mostly because TI uses the same filter in their datasheet plots.

AFIR4 mode, HQPlayer short@DSD128, sweep 0-20 kHz
AFIR4 mode, HQPlayer short@DSD128, IMD 19+20 kHz

As a summary, at least on this DAC, DSD128 has most limited ultrasonic output and no strongly correlated elements visible at all. For those using HQPlayer, "5.1" is best modulator option for this DAC.


  1. yamamoto2002's Avatar
    Thanks for posting. Very interesting. From the SHARP mode sweep graph, it seems UD-501 upsamples incoming 44.1kHz PCM signal to 352.8kHz PCM before entering DAC. And NOSDAC-like aliasing noise is seen in 352.8kHz +/- 22.5kHz
  2. Miska's Avatar
    Yes, the PCM1795 DAC chip has internal 8x digital filter that is disabled in the "NOS" mode. Rest of the oversampling is done using sample-and-hold (SAH) and that's why the aliasing noise around every 352.8 kHz. Most DAC chips have similar architecture of 8x interpolation plus SAH/linear interpolation and thus similar kind of response.
  3. yamamoto2002's Avatar
    Thanks for reply. Last year I created analog 3rd order butterworth LPF to eliminate this kind of aliasing noise . But I felt sound was more pleasing without this home-built circuit :)
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