As an audiophile reviewer, I recently needed to burn in some new gear. One was a review DAC loaner, the Calyx DAC 24/192, a nice piece from my initial listening tests. The others were a new set of Level 3 Reference Series speaker cables from AntiCable Audio, a set of Sopranino supertweeters from ENIGMAcoustics, and a Wireworld Starlight 7 USB cable that has benefited from prolonged burn–in. I’ve been using a circa 2000 track (44.1/16) from NASA Glenn that I have in my collection, and it was not doing it for me. So, over the weekend, I generated a series of higher rez test signals that I needed.
You may have noticed that folks are waking up to “high rez” audio. Heck, I literally wrote the book on high resolution file-based playback for the home. Now, the indicators are that consumers are willing to pay for higher quality downloadable music. Soon, Apple will flip the high rez switch in their IMS, which is the culmination of their Mastered for iTunes initiative which calls for replication masters at, “…any resolution above 16-bit 44.1kHz.”
The latest trend is portable high rez. This year’s RMAF showcased several battery-powered, pocket-sized DACs capable of better than 48 kHz sampling rate conversion. At the recent SXSW shindig, Neil Young finally came clean on his Pono initiative. I’ve been waiting four years since I first heard whisperings in San Rafael from my high rez engineering friends. I just purchased a yellow Pono player which, when delivered, will sit alongside a Geek Pulse Plus I ordered from LH Labs. That way, I’ll have some pieces to compare to my AK120 loaner from the nice folks at Astel & Kern.
Back to the test files. I chose 88.2 kHz sampling rate at 24 bits so the noise samples, pink and brown specifically, would contain sufficient high frequency energy while maintaining accurate low frequency performance with most DACs. You may be asking, “What’s with the colored noise stuff? Sounds like a setup to a bad punchline.” According to Wikipedia, pink noise “…or 1⁄f noise (sometimes also called flicker noise) is a signal or process with a frequency spectrum such that the power spectral density (energy or power per Hz) is inversely proportional to the frequency of the signal. In pink noise, each octave (halving/doubling in frequency) carries an equal amount of noise power.” Brown noise is a random audio signal or energy with a power density inversely proportional to frequency squared. The energy decreases by 6 dB per octave. Pink noise has less high frequency energy than white noise, while brown noise has less high frequency energy than pink noise.
Since I wanted to exercise speaker cables 24/7 while I wasn’t listening to music, it had to be a test signal that I could sleep through and wouldn’t cause my neighbors to go all lynch mob on me. I chose 20 Hz since, if you wire your speakers with one of the two having flipped polarity, the signals mostly cancel acoustically, and you won’t actually hear much if at all. Besides, most loudspeakers won’t even produce usable output at 20 Hz. While I was at it, I generated a few low frequency sweeps, great for checking cabinet and stand resonances, a 12 Hz tone for checking behavior at the very bottom of the spectrum, and a 20 Hz pulse. Being a pulse with a mix of both high and low frequencies, it’s audible no matter how cheesy your rig and regardless of the polarity of your speakers.
Being a pulse, its fundamental is at 20 Hz, while its pulsed nature brings ultrasonic harmonics. If I had used a lower sampling rate, I would not have captured those harmonics. Take a look at the illustration below. The x-axis is time, while the y-axis is frequency. Dark is large amplitude, while white is zero amplitude. You can graphically see the on-off nature of the pulses but, you can also see that there’s energy present past 20 kHz, which is useful for burning in items like those supertweeters I mentioned earlier. The red arrow at upper left is 20k, while the frequency cursor, that small blue pearl with its accompanying numeric callout, is parked at 39.889 kHz.
So, a variety of signals that should come in handy for your explorations as well as mine. I hope you find these useful. The files, 14 of them, were generated in software and are in ALAC format. The ZIP’d file collection is 439 MB in size. If you need them in the equally capable FLAC or a less ideal format like WAV or AIFF, they are easily transcoded since they are lossless. I use TMKK’s XLD or X Lossless Decoder, a fab and free transcoder utility for Mac OS. For you Win kidz, try ZiSun’s Apple Lossless FLAC Converter.Powered by Sidelines