(https://www.bbc.co.uk/sounds/play/m002gfzv)
As I wanted the Richard Stilgoe tribute to Tom Lehrer, I've extracted
the audio from this programme. It's nominally MPEG4 AAC, 48 kHz sample
rate (so in theory up to 24 kHz), 320 kbps, stereo.
1. It's definitely mono; my X-Y display is a straight diagonal line.
Apart from the "BBC Sounds" sting in the first four seconds, the
musician at 0:31 to 0:50, the Lehrer recordings at 4:19-4:48 and
6:15-6:39, Cleo Laine 8:10-8:38, and Nick Drake 10:46-11:~11:13, 12:31-12:5x*, and 15:13-15:39*. 17:05-17:27. 22:45-23:02 drama extract.
Maybe this is normal (maybe has been for decades?) - record individual speakers with a mono mic., but mix (really, weight) them so they appear
(only very slightly) at different positions? With the presenter centre.
I wouldn't really have noticed the varying position, but I _am_
listening on a laptop's internal speakers, so that's probably
understandable; I only really noticed when the mono line varied in angle slightly between speakers.
On 28/07/2025 23:15, J. P. Gilliver wrote:
Samira Ahmed (presenter): brickwalled at 17 kHz, as were the LehrerIs this not an MP4 'thing'? If you download a piece of music from
extracts.
YouTube with yt-dlp so you can choose the format, the MP4 ones all have
this 17 kHz limit whilst the Opus files don't.
The normal layout for recording these shows is with the participants sat round a table and each has their own microphone. The inserts are added
by the engineer. Quiz shows such as "Have I Got News For You" use a
table for each team and one for the judge and scorer, with a microphone
for each participant. There are photographs and videos available on line which show this. As you have noticed, stereo is simulated by panning the signals left and right in varying proportions. There are very good
reasons for this including room noise and keeping relative levels steady.
On 2025/7/29 19:38:0, John Williamson wrote:
[]
The normal layout for recording these shows is with the participants satBut each participant just collected with a single (mono) mic., which is
round a table and each has their own microphone. The inserts are added
by the engineer. Quiz shows such as "Have I Got News For You" use a
table for each team and one for the judge and scorer, with a microphone
for each participant. There are photographs and videos available on line
which show this. As you have noticed, stereo is simulated by panning the
signals left and right in varying proportions. There are very good
reasons for this including room noise and keeping relative levels steady.
then mixed in fixed proportion to the two channels, with the proportion differing from one speaker to another (presenter usually being 1:1,
i. e. centre). Interesting.>
On 29/07/2025 21:37, J. P. Gilliver wrote:
But each participant just collected with a single (mono) mic., which isIt also means that the vocal bits are 100% mono compatible with none of
then mixed in fixed proportion to the two channels, with the proportion
differing from one speaker to another (presenter usually being 1:1,
i. e. centre). Interesting.>
the phasing effects you would get using, say, a spaced pair.
On 2025/7/29 21:48:34, John Williamson wrote:
On 29/07/2025 21:37, J. P. Gilliver wrote:
[]
But each participant just collected with a single (mono) mic., which isIt also means that the vocal bits are 100% mono compatible with none of
then mixed in fixed proportion to the two channels, with the proportion
differing from one speaker to another (presenter usually being 1:1,
i. e. centre). Interesting.>
the phasing effects you would get using, say, a spaced pair.
Good point I hadn't thought of! Similar to the slight variable-comb
effects used when combining the channels from a stereo pickup playing a
mono record on a non-linear-tracking turntable.
J. P. Gilliver <[email protected]> wrote:
On 2025/7/29 21:48:34, John Williamson wrote:
It also means that the vocal bits are 100% mono compatible with none of
the phasing effects you would get using, say, a spaced pair.
Good point I hadn't thought of! Similar to the slight variable-comb
effects used when combining the channels from a stereo pickup playing a
mono record on a non-linear-tracking turntable.
...made even worse on early recordings by the recording engineer
twisting the recording stylus to help throw the swarf to one side. The
two 'channels' can be out of step by an amount which depends on how far
up the groove walls the elliptical playback stylus makes contact, so
even a parallel-tracker won't play them correctly unless the cartridge
is mounted on a swivel and can be offset to the correct angle.
At about 8 Kc/s, the HMV frequency test record can give almost purely circular movement to the stylus tip; the two groove walls are 90-degrees
out of phase with a 0025" radius elliptical stylus mounted orthogonally.
On 2025/7/30 8:31:10, Liz Tuddenham wrote:
J. P. Gilliver <[email protected]> wrote:
On 2025/7/29 21:48:34, John Williamson wrote:
[]
It also means that the vocal bits are 100% mono compatible with none of >>> the phasing effects you would get using, say, a spaced pair.
Good point I hadn't thought of! Similar to the slight variable-comb
effects used when combining the channels from a stereo pickup playing a
mono record on a non-linear-tracking turntable.
...made even worse on early recordings by the recording engineer
twisting the recording stylus to help throw the swarf to one side. The
I wasn't aware of that!
two 'channels' can be out of step by an amount which depends on how far
up the groove walls the elliptical playback stylus makes contact, so
even a parallel-tracker won't play them correctly unless the cartridge
is mounted on a swivel and can be offset to the correct angle.
(Which mine - Marantz TT520 - certainly isn't.)>
At about 8 Kc/s, the HMV frequency test record can give almost purely circular movement to the stylus tip; the two groove walls are 90-degrees out of phase with a 0025" radius elliptical stylus mounted orthogonally.
I presume that's a test record made before stereo? (What date _is_ it,
and what frequencies does it contain [assuming it has tones or a sweep],
out of interest?)
J. P. Gilliver <[email protected]> wrote:
I presume that's a test record made before stereo? (What date _is_ it,
and what frequencies does it contain [assuming it has tones or a sweep],
out of interest?)
One side of HMV DB4037 is a set of bands at different frequencies with
the highest, 8.6 Kc/s, on the outside to take advantage of the higher
surface speed. There are other sides in the set with fixed and sweep
tones, but none above 8.6 Kc/s. It was monophonic and was cut in 1936
with the Blumlein mono cutterhead, which had a particular problem with 'azimuth' offset. They were all recorded with a 'U'-bottomed groove,
which needs a truncated elliptical playback stylus for the best results
- and that is the type most affected by theoffset.
The Blumlein cutterhead had the cutting tip hung on the end of a
trailing cantilever which was swung from side to side by rotary movement
of a near-vertical shaft. If there was any misalignment of the cutting
face, the force it generated by throwing the swarf off to one side would
push it sideways and cause an even bigger misalignment. Because the restoring springs on the vertical shaft were not very stiff (to achieve
the correct resonant frequency), this misalignment could be quite considerable.
Another problem caused by the compliance of the springs was that the
rush of air into the suction pipe (which was fitted to remove the swarf)
had to be limited in order to prevent it disturbing the cutter; on
Columbia DX73 this is very obvious as a constant roaring background
noise. I imagine the operator would have been very tempted to
deliberately skew the cutter to aid swarf removal - although I have no
proof of that, other than a large number of discs recorded with the
Blumlein cutter which have considerable 'azimuth' errors.
On 2025/7/30 16:49:55, Liz Tuddenham wrote:
J. P. Gilliver <[email protected]> wrote:
[]
I presume that's a test record made before stereo? (What date _is_ it,
and what frequencies does it contain [assuming it has tones or a sweep], >> out of interest?)
One side of HMV DB4037 is a set of bands at different frequencies with
the highest, 8.6 Kc/s, on the outside to take advantage of the higher surface speed. There are other sides in the set with fixed and sweep tones, but none above 8.6 Kc/s. It was monophonic and was cut in 1936 with the Blumlein mono cutterhead, which had a particular problem with 'azimuth' offset. They were all recorded with a 'U'-bottomed groove,
which needs a truncated elliptical playback stylus for the best results
- and that is the type most affected by theoffset.
So 8.6 k (strange number!) was the highest it was thought worth worrying about in 1936. Interesting. (Do you have a chart of what was considered
a reasonablr bandwidth at various dates?) I'd have thought that rather
low for 1936, though couldn't justify that feeling if challenged.>
J. P. Gilliver <[email protected]> wrote:
So 8.6 k (strange number!) was the highest it was thought worth worrying
about in 1936. Interesting. (Do you have a chart of what was considered
a reasonablr bandwidth at various dates?) I'd have thought that rather
low for 1936, though couldn't justify that feeling if challenged.>
I think it was sufficient to cover the top resonance of the pickups of
the day, which was a major concern - and, yes, it was probably the
highest frequency they could sensibly record with the equipment they had
at EMI at that date. Higher frequencies than that were recorded by
slowing down the recording lathe, but this wasn't normal practice.
It wasn't until Arthur Haddy of Decca produced the FFRR recording system
that higher frequencies were recorded on commercial records (which made
Mantovani's strings famous). Haddy's cutterhead was copied from Voigts
moving coil design without acknowledgement; when Sugden later copied it
from Haddy, Haddy was furious but couldn't do anything about it.
For a much fuller explanation look at Peter Copeland's "Manual of
Analogue Audio Resoration Techniques". It is supposed to be on the
British Library's website but the page has vanished so you may have to download an archive copy. [That should keep you busy until I come back
from holiday.]
| Sysop: | Keyop |
|---|---|
| Location: | Huddersfield, West Yorkshire, UK |
| Users: | 715 |
| Nodes: | 16 (4 / 12) |
| Uptime: | 29:23:57 |
| Calls: | 12,108 |
| Calls today: | 8 |
| Files: | 15,006 |
| Messages: | 6,518,244 |