As Tom pointed out there's almost always something humming in the room if not just the field coil effect from the rooms AC wiring.
We tracked the coolers in the bar at The Riverboat on a Neil Young live show and it worked well enough to solve their problem, the result is in Archives Vol1.
Please pardon the mispellings and occassional insane word substitution I'm on an iPhone
> On Feb 27, 2016, at 4:03 AM, Nigel Champion <[log in to unmask]> wrote:
> Hi Jamie
> The Nakamichi 680ZX can record and play at half-speed (15/16ips) and has good reviews.
> How much hum would you expect on the battery-powered cassette recorder we're talking about here?
> From: Association for Recorded Sound Discussion List [[log in to unmask]] on behalf of Jamie Howarth [[log in to unmask]]
> Sent: 27 February 2016 19:18
> To: [log in to unmask]
> Subject: Re: [ARSCLIST] Cassettes that speed-up---what's up?
> I’ve never seen that, and i’m thinking something fairly low in frequency that was induced into the head could masquerade as bias — what frequency was it? Sony dictation machines were like 43kHz and that’s the best we’ve been able to see, did a job for an Atlanta outfit… The normal bias of like 100kHz doesn’t survive probably because of the thermal self-noise of the head.
> And as I said in the post, I would more likely track the hum. which would rise in pitch on playback from 60 to something like possibly 240 for a 1/4 speed slowdown. The LF recording works fine regardless of how slow the tape is going. Tape can record DC.
> I’d love to find a mechanism that would do 15/16IPS —— anybody know of a decent quality deck that will do that?
>> On Feb 26, 2016, at 8:11 PM, Ellis Burman <[log in to unmask]> wrote:
>> That might be quite challenging Jamie. I had one tape where the batteries
>> were obviously dying - the audio sped up greatly and became distorted and
>> very low level towards the end of the tape. Once I speed corrected it (by
>> ear - just matching the voice tonality at the end with that at the
>> beginning, and then determining the middle part (linear? or logarithmic?),
>> the bias was clearly audible in the later portion of the tape. I guess the
>> bias frequency was very dependent on the battery voltage and dropped down
>> to well within audio range, even with the very slow tape speed. All I can
>> say is "good luck with that one" as, at least in my case, the bias
>> frequency was not constant.
>>> On Fri, Feb 26, 2016 at 9:26 AM, Jamie Howarth <[log in to unmask]> wrote:
>>> Tyra - if you want them at fixed speed we can track the hum or room tone
>>> and put them back in constant natural pitch. PM me at
>>> [log in to unmask] if you like.
>>> Jamie Howarth
>>> Plangent Processes
>>> Please pardon the mispellings and occassional insane word substitution I'm
>>> on an iPhone
>>>> On Feb 26, 2016, at 11:57 AM, Tom Fine <[log in to unmask]>
>>>> Tyra, you could have cases where the recorder batteries were low, which
>>> would cause recording speed to slow down and playback speed to increase.
>>> I've run into that with oral histories. I usually don't even try to make
>>> the result "pitch perfect." Rather, I determine a point where playback
>>> speed has gotten so fast that the intelligability has decreased badly. I
>>> then go back a bit before that, and select to the end of the field. Then I
>>> pitch-alter it for the best overall audibility, again not worrying about
>>> "perfect pitch" but rather best audibility of the words being spoken. It
>>> depends on how fast and how clearly someone is speaking.
>>>> -- Tom Fine
>>>> ----- Original Message ----- From: "Grant, Tyra" <[log in to unmask]>
>>>> To: <[log in to unmask]>
>>>> Sent: Friday, February 26, 2016 11:42 AM
>>>> Subject: [ARSCLIST] Cassettes that speed-up---what's up?
>>>>> We're transferring a collection of personal
>>> cassettes---interviews---mainly from the 90s.
>>>>> A few start out okay then slowly speed-up so people sound like The
>>>>> Then, some are okay on one side but the flip side is speeded-up.
>>>>> What's up here?
>>>>> We'd appreciate recommendations re: the best way to handle these in
>>> order to get something listenable.
>>>>> Tyra Grant
>>>>> [log in to unmask]
>>>>> University of Kansas Libraries
>> [log in to unmask]