Radio Shack Optimus CD-3400 portable CD player Measurements part 2
Fig.5 RadioShack Optimus CD-3400, left-channel departure from linearity (2dB/vertical div.).
Fig.6, the waveform of an undithered, 1kHz sinewave at -90dB, provides further evidence that the CD-3400's low-level performance is noise-limited. The signal is swamped by audioband noise, making it difficult to make out the stepped waveshape. Our standard noise-modulation test (fig.7) reveals some shifting of the noise floor as a function of input level, along with a slightly changing spectral balance of the noise as the input signal changes.
Fig.6 RadioShack Optimus CD-3400, waveform of undithered 1kHz sinewave at -90.31dBFS.
Fig.7 RadioShack Optimus CD-3400, noise modulation, -60 to -100dBFS (10dB/vertical div.).
Looking at the CD-3400's intermodulation spectrum when the player was decoding a full-scale mix of 19kHz and 20kHz (fig.8) showed very few intermodulation products, and those were of low amplitude. The 1kHz difference product (20kHz minus 19kHz) almost reaches -90dB, while the presence of the peak at 24.1kHz indicates only moderate ultrasonic analog filtering.
Fig.8 RadioShack Optimus CD-3400, HF intermodulation spectrum, DC-22kHz, 19+20kHz at 0dBFS (linear frequency scale, 20dB/vertical div.).
The CD-3400's bench performance was only fair in the context of most of the products I test, but acceptable considering that it costs about ten times less than the average digital processor. Moreover, it had better technical performance than some poorly engineered high-end products. There is, however, nothing in the measurements that would indicate its high sonic performance-to-price ratio.—Robert Harley