Hi fellow Vintage Tech subscribers.
First post in this area, and I thought I'd make it about the voice-band modem technology which is fast fading away. The V.90 and V.92 standard are special, in that they exploited the fact that one side of the connection can be purely digital, and thus suffers less distortion from analog to digital conversion, and vice versa. As a result, V.90/92 connections can only happen with digital modem terminating gear, making them unlikely to be achieved once the existing modem banks operated by commercial ISPs are closed down.
The V.90 standard was a compromise standard that was incompatible with the warring x2 and K56flex standards of the early 56k days. The V.90 standard introduced a new signal, known as a Digital Impairment Learning (DIL), which is defined by the analog modem in a data segment known as Ja, and sent back from the digital modem so that the analog modem can learn of the impairments on the line (e.g. digital pads, robbed bit signalling). The way this is defined led to different chipsets having a different DIL due to their differing software algorithms.
In order to capture this, I bolstered my collection of modems, got my VoIP gear configured carefully to best pass data and made many test-calls to commercial ISP lines to reconstruct the calls and produce the highest quality samples which cover virtually all chipsets, with the exception of Topic/ICPlus.
You will find the post at:
http://goughlui.com/2016/05/03/project-the-definitive-collection-of-v-90v-92-modem-sounds/
I hope you enjoy it - feel free to browse the related modem collection, and project FAX area for more voice-band modem goodness.
- Gough
