Why 151k?

The 151.2 kHz frequency bridges the two audio sampling rates used by the Sony PlayStation console (and also, but less commonly, the Philips Green Book CD-i standard) — specifically, Philips' CD-i 37.8 kHz and Sony's CD-DA 44.1 kHz rates.(¹)

This means that 151k players can combine the 37.8 kHz and 44.1 kHz sources from PlayStation games (or CD-i discs, including Green Book video CDs), via a third frequency that's a simple integer ratio to both. In other words, the cleanest possible resample of the content can be applied to both types of source equally, without giving preference to one over the other.

For example, consider the prime factors of these PCM sampling frequencies:

37800 == 7¹ x 5² x 3³ x 2³
44100 == 7² x 5² x 3² x 2²
151200 == 7¹ x 5² x 3³ x 2⁵

As a result, 151200 == 37800 x 2² and 151200 == 44100 x (2³ x 3) / 7.

To be complete, 75600 is more closely related (i.e. simpler harmonic relationship):

75600 == 37800 x 2, and 75600 == 44100 x (2² x 3) / 7.

However, 151k is the better choice in practice due to the recent shift to a 48 kHz standard for smartphones and other digital audio devices, and the fact that 96 kHz sources are common:

151200 == 37800 x 2², and 151200 == 44100 x (2³ x 3) / 7, and 151200 == 48000 x (3² x 7) / (2² x 5).

151.2 kHz connects all three of these sampling densities, plus Mitsubishi X-80 50.4 kHz and Bell System 8/16/32 kHz, with minimal multiplication and division, while also neatly sitting at the upper end of the Hi-Res range, which caps at 192 kHz.

Additionally, although somewhat orthogonally, 151k is of a similar magnitude to the Audion intermediate frequency of 150 kc/s, by Edwin Armstrong, and the +/- 75 kc/s FCC standard FM Stereo channel carrier limit.

Please contact mchg [at] expressionlogic dot com for more info, corrections, or questions.

(¹): In addition to Philips Green Book (and Microsoft CD-XA), 37.8 kHz was also part of a Panasonic Avionics patent describing in-flight / in-vehicle entertainment systems (patent US5953429A), with reference to a preferred composite transfer rate of 19.3536 MHz.