Scott, I want to thank you very much for the two files that you uploaded.
In case anyone was wondering (if not, stop reading now!), the reason why I had requested a file was that I have years of experience working with digital audio (in many different file formats and data types including linear PCM, non-linear PCM, and both lossless codecs and lossy codecs) and had read that the files created by the AR-DV1 used a 19.2 kHz (19200 Hz) sampling rate.
What struck me was that I couldn't recall
ever having dealt with an audio file of any type/format (or the audio track of a video file) where a 19.2 kHz sampling rate was used, so I just wanted to confirm for my own curiosity whether the reported figure of 19.2 kHz was accurate.
Looking at the files Scott supplied, in multiple programs, I find that the sampling rate is indeed 19.2 kHz. Here, for example, is what
MediaInfo Lite reports for each of the two files.
Code:
Format : PCM
Format settings, Endianness : Little
Format settings, Sign : Signed
Codec ID : 1
Duration : 13s 653ms
Bit rate mode : Constant
Bit rate : 307 Kbps
Channel(s) : 1 channel
Sampling rate : 19.2 KHz
Bit depth : 16 bits
Usually when someone wants to produce some relatively low-grade audio, they'll use a sampling rate of 8, 16, or 32 kHz if in old-school mode. In the more modern world, they'll typically use 11.025 or 22.050 kHz sampling.
For audio CDs and many other mostly consumer applications, 44.1 kHz will be used.
For video, 48 kHz will usually be used.
For serious recording, such as in recording studios and even many home recording setups, when it's desired to use a multiple of the audio CD rate of 44.1 kHz, either 88.2 or 176.4 kHz will be used. If the audio CD rate of 44.1 kHz is of no concern, then 96, 192, or even (for the true extremists in the crowd) 384 kHz will be used.
For recording the voice communications audio output of a product such as the AOR AR-DV1, a sampling rate of 8 kHz or 11.025 kHz is sufficient as it meets the requirements of
Nyquist–Shannon.
I would love to know where they came up with 19.2 kHz. In my imagination, I picture one of the AOR engineers as being an audiophile in his private life - or else moonlighting in a recording studio after his day job - and dealing with quality ADCs and DACs (analog-to-digital converters and digital-to-analog converters, respectively) and he's sitting there one day (evening) looking up at the front panel of one of these devices and seeing '19.2 kHz' marked on the front panel and saying to himself, "we can get by with one-tenth of that for the AR-DV1 since we're only recording voice traffic".
Just to ensure that I wasn't loosing it in my old age, I even checked Wikipedia to see what it had to say and, as expected, 19,200 Hz is not to be found on their list of "common audio sample rates".
Sampling (signal processing) - Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Sampling_(signal_processing)
Since computer sound cards don't natively support a 19.2 kHz sampling rate, the operating system, at least in the case of Windows, must perform a sample rate conversion (to a rate supported by the installed sound card/sound device) prior to sending the audio data stream to the card for D-to-A conversion.
Along with the digital audio sampling rate used in recorded files, I was also curious about the statement on page 32 - Section 5-4 - of the AR-DV1 manual where it says, "The recorded files contain the recorded time, receiving frequency, receive mode, signal strength and receive mode."
Being the curious type, I wanted to know exactly how this information was stored in the .wav files produced by the AR-DV1. I figured that AOR might be using the EBU BWF (European Broadcasting Union - Broadcast Wave Format) that adds additional chunks to the standard Microsoft RIFF (Resource Interchange File Format) WAVE file format, or maybe they were using some of the old standard RIFF WAVE chunks to store this information.
Well, as it turns out, I examined the two files posted by Scott and although it appears that there are some extra chucks in the files, they don't conform to the EBU BWF specification and actually appear to be to non-standard. In fact, one of the programs that I used claimed that the files contained an "invalid chuck", and refused to open either of them.
The end result was that I was not able to decode any of the information that AOR says is included in the files. I even looked at each of the files in a hex editor program, but wasn't able to identify any human-readable information aside from the usual RIFF WAVE header stuff, so if the information is there, apparently a specially-written application program will be required in order to extract and display it.
And again, thank you Scott for posting the files. It is much appreciated.
Regards,
Frank.
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