Appendix 1: A ‘Tarnished Test’ Signal

The files submitted [1] contained computer-generated test signals interleaved with the music. We assume that the music segments were included to ‘trick’ the encoder into treating it as music.

The screen capture below shows (upper in green) the waveform of L & R channels throughout the 88.2kHz input signal. Below that (in red/orange) is their spectral content.  The 44.1kHz file was similar. The signal was out of gamut in several places, including ‘overs’ of +0.72dB, and the impulse. The files contained significant ‘washboard’ distortion.[2]

The 88.2 kHz composite signal has these sections (left to right):

  • Silence
  • Music (upsampled from 44.1k/16b)
  • An impulse
  • Ultrasonic twin tone at full scale
  • Music repeated
  • White noise
  • Square wave
  • Music repeated
  • Multitone test
  • RMAA test sequence


 In the graph opposite, we see the spectrum of the full-scale white-noise segment in brown. [3]
Red shows the spectral maximum and Blue the noise-floor for the Music segments (noise-floor ~12 bit at 5kHz); note the brick-wall upsampling.
The noise floor of the various segments alternated between 24-, 22-, 12- and 6-bit levels.
For reference, the Green line is the noise-floor of an 88.2 kHz/16b channel.

The content of these files does not in any way represent music, as we show in the next Appendix.

Appendix 2:  Test Signals and Music


[1] Files from the blogger’s download link.

[2] See Dither paper: Stuart, J. Robert; Craven, Peter G., ‘The Gentle Art of Dithering’, JAES Volume 67 Issue 5 pp. 278-299; May 2019. Open Access

[3] Throughout these appendices, we have used FFT analysis with 21.5Hz bin-width as this can give reasonable agreement between noise and tonal signals at low frequencies as this corresponds to the narrowest (equivalent rectangular bandwidth) ERB for human listeners. (For more detail see: J. R. Stuart, “Noise: Methods for Estimating
Detectability and Threshold,” J. Audio Eng. Soc., vol.
42, pp. 124–140 (1994 Mar.). on AES website )


A Deeper Look (Home)

All that glitters is not gold(en)

Appendix 2:  Test Signals and Music

Appendix 3: The Musical Triangle

Appendix 4: MQA Encoding